Dr Rita Jabr

Senior Lecturer in Cardiac Electrophysiology
+44 (0)1483 684618
12 AY 04

University roles and responsibilities

  • Senior Lecturer in Cardiac Electrophysiology

Previous roles

Lecturer in Cardiac Electrophysiology
University of Surrey
Senior Research Fellow
Department of Cardiac Electrophysiology, National Heart and Lung Institute, Imperial College London
Senior Research Fellow
Cardiovascular Division, Department of Cardiology, The Rayne Institute, King's College London
Honorary Lecturer/Senior Research Fellow
Centre for Clinical Pharmacology and Toxicology, Department of Medicine, University College London
Assistant Professor
Department of Physiology, Faculty of Medicine, Kuwait University
Postdoctoral Fellow
Department of Physiology and Cell Biology, School of Medicine, University of Nevada
PhD Student
Physiology Department, University of Manitoba

Affiliations and memberships

AES (Qatar Foundation's premier intellectual exchange network and Arab science revival initiative)
British Society for Cardiovascular Research
International Society for Heart Research
Physiological Society UK
Royal Society of Medicine


Research interests

Research collaborations

Technical skills


  • Patch-clamp technique
  • Intracellular microelectrode or extracellular monophasic action potential recording simultaneously with isometric muscle contractions
  • Tissue impedance measurement
  • Multi-electrode array system
  • Dielectrophoresis

Muscle contraction

  • Recording isometric muscle contractions in cardiac and smooth muscle preparations
  • Measurement of isolated cardiomyocyte mechanics

Imaging techniques

  • Immunofluorescence with laser scanning confocal microscopy
  • Real-time intracellular Ca2+ imaging by epifluorescence microscopy, cell shortening by video-scanning methods


  • Protein phosphatase activity assays
  • Subcellular tissue fractionation
  • SDS-PAGE and western blotting
  • PCR
  • Mouse genotyping
  • Baculovirus protein expression system.

Cell preparation

  • Single cardiac and vascular smooth muscle cells isolation techniques

Tissue culture

  • Primary and cell-line tissue culture
  • Proliferation assay


  • 2013-2015 (£128,000; PI: R Jabr, Co-I: CH Fry). Title: Investigation of the role of calcineurin in persistent electrophysiological myocardial changes following regression from left ventricular hypertrophy. Funded by British Heart Foundation
  • 2013-2014 (£8,000; Co-PI: R Jabr). Title: MicroRNAs as potential biomarkers in coronary artery calcification. Biomedical & Health Research Pump-Priming Funds grant, University of Surrey, 2011-2015 (£638,000) HASTE Foundation. Title: Improving detection and characterising the fundamental basis of atrial fibrillation. I am the Lead on the investigative research component (Dr E Leatham is lead on the clinical component and Prof CH Fry the manager of both components)
  • 2008-2010 (£147,280; PI: R Jabr, Co-I: CH Fry). Title: The role of calcineurin in regulating action potential propagation in normal and hypertrophied myocardium through connexin43 dephosphorylation. Funded by British Heart Foundation
  • 2009-2012 (€300,000; PI: CH Fry; Co-I, R Jabr). Title: Combatting Incontinence: InComb-EU Framework 7. 
  • 1999-2000 (£80,000- PI R Jabr). Title: Contractile and electrophysiological properties of cardiac ventricular myocytes in spontaneously hypertensive rats before and during development of hypertension, 1999. Funded by Kuwait University.

Invited research lectures

  • 2012 Centre for Cardiovascular investigation; Faculty of Medicine; University of La Plata. Title: The differential role of calcineurin isoforms in the cardiovascular system.
  • 2011 Physiological Society Meeting, Oxford, July, 2011 Title: Inter-relationship between conduction velocity, intracellular Ca2+ and gap junction resistance in ventricular myocardium
  • 2011 University of Surrey, FHMS, research day, 'Hot topics in cardiovascular research'. Title: Cellular mechanisms for cardiac arrhythmogenesis.
  • 2010 Pfizer, sandwich, UK. Title: Role of calcineurin in overactive bladder.
  • 2010 The FP7 mid-term meeting, UK. Title: Use of the dielectrophoresis technique for selective cell sorting of bladder urothelial cells.
  • 2009 The European Society of Cardiology, Munich, Germany. Title: Calcineurin nuclear import.
  • 2009 The Marie Curie- Nuclear Receptors Biology Meeting, UK. Title: Role of nuclear calcineurin in the heart.
  • 2008 UK Gap Junction meeting, University of Surrey, UK. Title: Calcineurin slows conduction velocity during rapid pacing in guinea pig papillary muscle.


Postgraduate research supervision

Completed postgraduate research projects I have supervised

My teaching

My publications


Fry CH, Young JS, Jabr RI, McCarthy C, Ikeda Y, Kanai AJ (2012) Modulation of spontaneous activity in the overactive bladder ? the role of P2Y agonists,American Journal of Physiology, Renal Physiology 302 (11) pp. F1447-F1454 Wiley
Spinal cord transection (SCT) leads to an increase of spontaneous contractile activity in the isolated bladder that is reminiscent of an overactive bladder syndrome in patients with similar damage to the central nervous system. An increase of interstitial cell number in the suburothelial space between the urothelium and detrusor smooth muscle layer occurs in SCT bladders and these cells elicit excitatory responses to purines and pyrimidines such as ATP, ADP and UTP. We have investigated the hypothesis that these agents underlie the increase of spontaneous activity. Rats underwent lower thoracic spinal cord transection and their bladder sheets or strips, with intact mucosa except where specified, used for experiments. Isometric tension was recorded and propagating Ca2+ and membrane potential (Em) waves recorded by fluorescence imaging using photodiode arrays. SCT bladders were associated with regular spontaneous contractions (2.9±0.4 min-1); ADP, UTP and UDP augmented the amplitude but not their frequency. With strips from such bladders, a P2Y6-selective agonist (PSB0474) exerted similar effects. Fluorescence imaging of bladder sheets showed that ADP or UTP increased the conduction velocity of Ca2+/Em waves that were confined to regions of the bladder wall with an intact mucosa. When transverse bladder sections were used, Ca2+/Em waves originated in the suburothelial space and propagated to the detrusor and urothelium. Analysis of wave propagation showed that the suburothelial space exhibited properties of an electrical syncitium. These experiments are consistent with the hypothesis that P2Y-receptor agonists increase spontaneous contractile activity by augmenting functional activity of the cellular syncitium in the suburothelial space.
Fry CH, Salvage SC, Manazza A, Dupont E, Labeed FH, Hughes MP, Jabr RI (2012) Cytoplasm resistivity of Mammalian atrial myocardium determined by dielectrophoresis and impedance methods., Biophys J 103 (11) pp. 2287-2294
Many cardiac arrhythmias are caused by slowed conduction of action potentials, which in turn can be due to an abnormal increase of intracellular myocardial resistance. Intracellular resistivity is a linear sum of that offered by gap junctions between contiguous cells and the cytoplasm of the myocytes themselves. However, the relative contribution of the two components is unclear, especially in atrial myocardium, as there are no precise measurements of cytoplasmic resistivity, R(c). In this study, R(c) was measured in atrial tissue using several methods: a dielectrophoresis technique with isolated cells and impedance measurements with both isolated cells and multicellular preparations. All methods yielded similar values for R(c), with a mean of 138 ± 5 ©·cm at 23°C, and a Q(10) value of 1.20. This value is about half that of total intracellular resistivity and thus will be a significant determinant of the actual value of action potential conduction velocity. The dielectrophoresis experiments demonstrated the importance of including divalent cations (Ca(2+) and Mg(2+)) in the suspension medium, as their omission reduced cell integrity by lowering membrane resistivity and increasing cytoplasm resistivity. Accurate measurement of R(c) is essential to develop quantitative computational models that determine the key factors contributing to the development of cardiac arrhythmias.
Fry CH, Jabr RI (2010) The action potential and nervous conduction,Surgery 28 (2) pp. 49-54
An action potential is a transient depolarization of the membrane potential of excitable cells. They serve two main functions: to transmit and encode information, and to initiate cellular events such as muscular contraction. In this article action potentials generated in nerves will be the focus of attention. An action potential results from a transient change to the properties of the cell membrane, from a state where it is much more permeable to K+ than Na+, to a reversal of these permeability properties. Thus during the action potential an influx of Na+ is responsible for the rapid depolarization and an efflux of K+ causes repolarization. This ionic basis of the action potential can be predicted from the Nernst equation and is illustrated in the text. Changes to membrane ionic permeability are due to the opening and closing of voltage-gated ion channels, and the properties of such channels explain additional phenomena such as refractoriness, threshold and cellular excitability. Action potentials conduct with a finite velocity along nerve axons, and the actual velocity depends on a number of factors that include: fibre radius, temperature, functional ion channel number and the presence of a myelin sheath. The physical basis of conduction is explained by the local circuit hypothesis. Synaptic transmission of an action potential is explained in terms of excitatory post-synaptic potential (EPSP) generation at the post-synaptic membrane. The facility by which post-synaptic action potential may be developed is explained in terms of temporal and spatial summation as well as the influence of inhibitory transmitters. © 2010 Elsevier Ltd. All rights reserved.
Jabr RI, Fry CH (2013) Animal Models of Lower Urinary Tract Dysfunction, pp. 461-481
The function of the lower urinary tract is to store urine and periodically expel its contents through a reciprocal control of the contractile properties of the urinary bladder and its outflow tract. The decision to switch from storage to voiding modes depends upon integrating, in the central nervous system, sensory information from the bladder and controlling lower urinary tract function from the sacral spinal cord. Pathological or congenital alterations to any stage of this process can induce a combination of symptoms that include urgency and frequency, leakage of urine or pain. Animal models can be generated to characterise different stages of this complex control process to understand the particular biological defects that can lead to these pathologies. This chapter will address a number of lower urinary tract pathologies and how animal models can help in understanding them. © 2013 Elsevier Inc. All rights reserved.
Mesquita RFDS, Paul MA, Francois A, Jabr R, Marber MS, Heads RJ, Valmaseda A, Anjum S, Budhram-Mahadeo V (2014) Protein kinase Ce{open};-calcineurin cosignaling downstream of toll-like receptor 4 downregulates fibrosis and induces wound healing gene expression in cardiac myofibroblasts, Molecular and Cellular Biology 34 (4) pp. 574-594
The pathways which regulate resolution of inflammation and contribute to positive remodeling of the myocardium following injury are poorly understood. Here we show that protein kinase C epsilon (PKC) cooperates with the phosphatase calcineurin (CN) to potentiate induction of cardioprotective gene expression while suppressing expression of fibrosis markers. This was achieved by detailed analysis of the regulation of cyclooxygenase 2 (COX-2) expression as a marker gene and by using gene expression profiling to identify genes regulated by coexpression of CN-A/PKC in adult rat cardiac myofibroblasts (ARVFs) on a larger scale. GeneChip analysis of CN-A±/PKC-coexpressing ARVFs showed that COX-2 provides a signature for wound healing and is associated with downregulation of fibrosis markers, including connective tissue growth factor (CTGF), fibronectin, and collagens Col1a1, Col3a1, Col6a3, Col11a1, Col12a1, and Col14a1, with concomitant upregulation of cardioprotection markers, including COX-2 itself, lipocalin 2 (LCN2), tissue inhibitor of metalloproteinase 1 (TIMP-1), interleukin-6 (IL-6), and inducible nitric oxide synthase (iNOS). In primary rat cardiomyocyte cultures Toll-like receptor 4 (TLR4) agonist- or PKC/CNdependent COX-2 induction occurred in coresident fibroblasts and was blocked by selective inhibition of CN or PKC ±/ or elimination of fibroblasts. Furthermore, ectopic expression of PKC and CN in ARVFs showed that the effects on COX-2 expression are mediated by specific NFAT sites within the COX-2 promoter as confirmed by site-directed mutagenesis and chromatin immunoprecipitation (ChIP). Therefore, PKC may negatively regulate adverse myocardial remodeling by cooperating with CN to downregulate fibrosis and induce transcription of cardioprotective wound healing genes, including COX-2. © 2014, American Society for Microbiology.
Fahmi A, Smart N, Punn A, Jabr R, Marber M, Heads R (2012) p42/p44-MAPK and PI3K are sufficient for IL-6 family cytokines/gp130 to signal to hypertrophy and survival in cardiomyocytes in the absence of JAK/STAT activation, Cellular Signalling 25 (3) Elsevier
The effect of differential signalling by IL-6 and leukaemia inhibitory factor (LIF) which signal by gp130 homodimerisation or LIFR²/gp130 heterodimerisation on survival and hypertrophy was studied in neonatal rat cardiomyocytes. Both LIF and IL-6 [in the absence of soluble IL-6 receptor (sIL-6R±)] activated Erk1/2, JNK1/2, p38-MAPK and PI3K signalling peaking at 20min and induced cytoprotection against simulated ischemia-reperfusion injury which was blocked by the MEK1/2 inhibitor PD98059 but not the p38-MAPK inhibitor SB203580. In the absence of sIL-6R, IL-6 did not induce STAT1/3 phosphorylation, whereas IL-6/sIL-6R and LIF induced STAT1 and STAT3 phosphorylation. Furthermore, IL-6/sIL-6R induced phosphorylation of STAT1 Tyr(701) and STAT3 Tyr(705) were enhanced by the p38-MAPK inhibitor SB203580. IL-6 and pheneylephrine (PE), but not LIF, induced cardiomyocyte iNOS expression and nitric oxide (NO) production. IL-6, LIF and PE induced cardiomyocyte hypertrophy, but with phenotypic differences in ANF and SERCA2 expression and myofilament organisation with IL-6 more resembling PE than LIF. Transfection of cardiomyocytes with full length or truncated chimaeric gp130 cytoplasmic domain/Erythropoietin receptor (EpoR) extracellular domain fusion constructs showed that the membrane proximal Box 1 and Box 2 containing region of gp130 was necessary and sufficient for MAPK and PI3K activation; hypertrophy; SERCA2 expression and iNOS/NO induction in the absence of JAK/STAT activation. In conclusion, IL-6 can signal in cardiomyocytes independent of sIL-6R and STAT1/3 and furthermore, that Erk1/2 and PI3K activation by IL-6 are both necessary and sufficient for induced cardioprotection. In addition, p38-MAPK may act as a negative feedback regulator of JAK/STAT activation in cardiomyocytes.
Fry CH, Jabr RI (2014) T-type Ca channels and the urinary and male genital tracts, Pflugers Archiv European Journal of Physiology 466 (4) pp. 781-789
T-type Ca channels are widely expressed throughout the urinary and male genital tracts, generally alongside L-type Ca channels. The use of pharmacological blockers of these channels has suggested functional roles in all regions, with the possible exception of the ureter. Their functional expression is apparent not just in smooth muscle cells but also in interstitial cells that lie in close proximity to muscle, nerve and epithelial components of these tissues. Thus, T-type Ca channels can contribute directly to modulation of muscle function and indirectly to changes of epithelial and nerve function. T-type Ca channel activity modulates phasic contractile activity, especially in conjunction with Ca -activated K channels, and also to agonist-dependent responses in different tissues. Upregulation of channel density occurs in pathological conditions associated with enhanced contractile responses, e.g. overactive bladder, but it is unclear if this is causal or a response to the pathological state. Moreover, T-type Ca channels may have a role in the development of prostate tumours regulating the secretion of mitogens from neuroendocrine cells. Although a number of selective channel blockers exist, their relative selectivity over L-type Ca channels is often low and makes evaluation of T-type Ca channel function in the whole organism difficult. © 2014 Springer-Verlag.
Fry CH, Gray RP, Dhillon PS, Jabr RI, Dupont E, Patel PM, Peters NS (2014) Architectural Correlates of Myocardial Conduction: Changes to the Topography of Cellular Coupling, Intracellular Conductance, and Action Potential Propagation with Hypertrophy in Guinea-Pig Ventricular Myocardium,Circulation: Arrhythmia and Electrophysiology 7 pp. 1198-1204 American Heart Association, Inc.
Background?We tested the hypothesis that alterations to action potential conduction velocity (CV) and conduction
anisotropy in left ventricular hypertrophy are associated with topographical changes to gap-junction coupling and
intracellular conductance by measuring these variables in the same preparations.
Methods and Results?Left ventricular papillary muscles were excised from aortic-banded or sham-operated guinea-pig
hearts. With intracellular stimulating and recording microelectrodes, CV was measured in 3 dimensions with simultaneous
conductance mapping with subthreshold stimuli and correlated with quantitative histomorphometry of myocardial
architecture and connexin 43 distribution. In hypertrophied myocardium, CV in the longitudinal axis was smaller and
transverse velocity was greater compared with control; associated with similar differences of intracellular conductance,
consistent with more cell contacts per cell (5.7±0.2 versus 8.1±0.5; control versus hypertrophy), and more intercalated
disks mediating side-to-side coupling (8.2±0.2 versus 10.2±0.4 per cell). Intercalated disk morphology and connexin 43
immunolabelling were not different in hypertrophy. Hypertrophied preparations showed local submillimeter (H250 ¼m)
regions with slow conduction and low intracellular conductance, which, although not affecting CV on the millimeter
scale, were consistent with discontinuities from increased microscopical connective tissue content.
Conclusions?With myocardial hypertrophy, altered longitudinal and transverse CV, and greater nonuniformity of CV anisotropy
correspond to changes of intracellular conductance. These are associated with alteration of myocardial architecture, specifically
the topography of cell?cell coupling and gap-junction connectivity.
Jabr R, Obasanjo-Blackshire K, Mesquita R, Molkentin JD, Hart SL, Marber MS, Xia Y, Heads RJ (2006) Calcineurin regulates NFAT-dependent iNOS expression and protection of cardiomyocytes: Co-operation with Src tyrosine kinase, Journal of Molecular and Cellular Cardiology 71 pp. 672-683
Objective: To determine the role of calcineurin and Src tyrosine kinase in the regulation of inducible nitric oxide synthase (iNOS) expression
and protection in cardiomyocytes.
Methods: iNOS expression was studied in isolated neonatal rat ventricular myocyte cultures in response to bacterial lipopolysaccharide
(LPS) or following transfection with constitutively active calcineurin or Src and in hearts isolated from wild-type or calcineruin A² knockout
mice. Cell injury in response to simulated ischemia?reperfusion was studied following overexpression of active calcineurin. Regulation of
the iNOS gene promoter by calcineurin was studied using promoter-luciferase reporter and chromatin immunoprecipitation assays.
Results: Overexpression of constitutively active Src co-operated with [Ca2+]c elevation to induce iNOS expression, and LPS-induced iNOS
expression was abrogated by pharmacological inhibition of calcineurin or tyrosine kinase. LPS also induced tyrosine kinase-dependent but
calcineurin-independent phosphorylation of Src Tyr418. LPS induced myocardial iNOS expression in wild-type but not calcineurin A²
knockout mice. Overexpression of constitutively active calcinuerin in isolated cardiomyocytes caused deposphorylation and nuclear
accumulation of the c1 isoform of nuclear factor of activated T-cells (NFATc1), induced strong iNOS expression, and induced NOSdependent
protection against simulated ischemia?reperfusion prior to cardiomyocyte hypertrophy. Co-transfection of a mouse iNOS
promoter-luciferase reporter in combination with active calcineurin and wild-type or dominant negative Src confirmed that constitutive
activation of calcineurin was sufficient for transactivation. Chromatin immunoprecipitation confirmed calcineurin-dependent in vivo binding
of NFATc1 to consensus sites within the iNOS promoter.
Conclusions: These results support a cardioprotective role for calcineurin mediated by NFAT-dependent induction of iNOS expression and
co-operativity between calcineurin and Src.
Jabr R, Wilson AJ, Riddervold MH, Jenkins AH, Perrino BA, Clapp LH (2007) Nuclear translocation of calcineurin A but not calcineurin A by platelet-derived growth factor in rat aortic smooth muscle, American Journal of Physiology: Cell Physiology 292 pp. c2213-c2225
regulates the proliferation of many cell types through activation
of the nuclear factor of activated T cells (NFAT). Two main
isoforms of the calcineurin catalytic subunit [calcineurin A (CnA)
and CnA ] have been identified, although their expression and function
are largely unknown in smooth muscle. Western blot analysis and
confocal imaging were performed in freshly isolated and cultured rat
aortic myocytes to identify these CnA isoforms and elucidate the
effect of PDGF on their cellular distribution and interaction with
NFAT isoforms. CnA and CnA isoforms displayed differential
cellular distribution, with CnA being evenly distributed between the
nucleus and cytosol and CnA being restricted to the cytosol. In
contrast with the rat brain, we found no evidence for particulate/
membrane localization of calcineurin. PDGF caused significant nuclear
translocation of CnA and induced smooth muscle cell proliferation,
with both effects being abrogated by the calcineurin inhibitor
cyclosporin A, the novel NFAT inhibitors A-285222 and inhibitor of
NFAT-calcineurin association-6, and the adenylyl cyclase activator
forskolin. PDGF also caused cyclosporin A-sensitive translocation of
NFATc3, with no apparent effect on either CnA or NFATc1 distribution.
Moreover, 87% of nuclear CnA was found to colocalize with
NFATc3, consistent with the finding that CnA bound more avidly than
CnA to a glutathione S-transferase-NFATc3 fusion protein. Based on
their differential distribution in aortic muscle, our results suggest that
CnA and CnA are likely to have different cellular functions. However,
CnA appears to be specifically activated by PDGF, and we postulate
that calcineurin-dependent nuclear translocation of NFATc3 is involved
in smooth muscle proliferation induced by this mitogen.
Howlett P, Morritt J, Greswell L, Findlay N, Mahmoudi M, Waheed A, Jabr R, Fry C, Leatham E (2014) 81Symptom frequency is a poor predictor of onset of paroxysmal atrial fibrillation in a population presenting with palpitations., Europace 16 Suppl 3
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and paroxysmal AF (PAF) comprises approximately half of all AF cases. PAF poses a particular diagnostic challenge given its intermittency. A physician's choice of investigational device is largely based on symptom frequency although it has been widely established that a significant proportion of PAF episodes are asymptomatic. We aim to determine whether symptom frequency is a reliable method to select a choice of investigational device in a population presenting with palpitations.
Jabr R, Fry CH (2013) Animal models of lower Urinary Tract Dysfunstion, In: Conn PM (eds.), Animal models for the study of human disease. 20 Elsevier (Academic Press)
Howlett PJ, Hatch FS, Alexeenko V, Jabr RI, Leatham EW, Fry CH (2015) Diagnosing Paroxysmal Atrial Fibrillation: Are Biomarkers the Solution to This Elusive Arrhythmia?,BioMed Research International 2015 910267 Hindawi Publishing Corporation
Atrial fibrillation (AF) is the commonest sustained arrhythmia globally and results in significantly increased morbidity and mortality including a fivefold risk of stroke. Paroxysmal atrial fibrillation (PAF) constitutes approximately half of all AF cases and is thought to represent an early stage of the disease. This intermittent form of atrial arrhythmia can be a challenge to identify and as a result many affected individuals are not prescribed appropriate antithrombotic therapy and hence are at risk of stroke and thromboembolism. Despite these adverse outcomes there have been relatively few diagnostic advances in the field since the introduction of the Holter monitor in 1949. This review aims to establish the available evidence for electrophysiological, molecular, and morphological biomarkers to improve the detection of PAF with reference to the underlying mechanisms for the condition.
Dhillon PS, Gray R, Kojodjojo P, Jabr R, Chowdhury R, Fry CH, Peters NS (2013) Relationship Between Gap-Junctional Conductance and Conduction Velocity in Mammalian Myocardium, CIRCULATION-ARRHYTHMIA AND ELECTROPHYSIOLOGY 6 (6) pp. 1208-1214 LIPPINCOTT WILLIAMS & WILKINS
Howlett PJ, Morritt J, Jabr R, Mahmoudi M, Fry CH, Leatham EW (2014) 70Targeted screening for paroxysmal atrial fibrillation: prolonged monitoring significantly increases diagnostic yield., Europace 16 Suppl 3
Atrial fibrillation (AF) is the most common cardiac arrhythmia. Paroxysmal AF (PAF) comprises approximately half of AF cases and confers an equivalent risk of thromboembolism. PAF poses a particular diagnostic challenge given its variable frequency, potential brevity and frequent lack of symptoms. Currently no definitive method to identify PAF has been proposed although 24-hour and 1-week monitoring remains common practice. We aim to determine whether the prolonged use of a handheld ECG monitor is an effective investigational tool to improve the diagnosis of PAF in a targeted population.
Dhillon PS, Gray R, Kojodjojo P, Jabr R, Chowdhury RA, Fry CH, Peters NS (2009) The Relationship Between Gap Junction Conductance and Conduction Velocity in Intact Myocardium, CIRCULATION 120 (18) pp. S621-S621 LIPPINCOTT WILLIAMS & WILKINS
Jabr R, Hatch, FS, Salvage SC, Orlowski A, Lampe PD, Fry CH (2016) Regulation of gap junction conductance by calcineurin through Cx43 phosphorylation: implications for action potential conduction,Pfluegers Archiv: European journal of physiology
Cardiac arrhythmias are associated with raised intracellular [Ca2+] and slowed action potential conduction caused by reduced gap junction (GJ) electrical conductance (Gj). Ventricular GJs are composed of connexin proteins (Cx43), with Gj determined by Cx43 phosphorylation status. Connexin phosphorylation is an interplay between protein kinases and phosphatases but the precise pathways are unknown. We aimed to identify key Ca2+-dependent phosphorylation sites on Cx43 that regulate cardiac gap junction conductance and action potential conduction velocity. We investigated the role of the Ca2+-dependent phosphatase, calcineurin. Intracellular [Ca2+] was raised in guinea-pig myocardium by a low-Na solution or increased stimulation. Conduction velocity and Gj were measured in multicellular strips. Phosphorylation of Cx43 serine residues (S365 and S368) and of the intermediary regulator I1 at threonine35 was measured by Western blot. Measurements were made in the presence and absence of inhibitors to calcineurin, I1 or protein phosphatase-1 and phosphatase-2.

Raised [Ca2+]i decreased Gj, reduced Cx43 phosphorylation at S365 and increased it at S368; these changes were reversed by calcineurin inhibitors. Cx43-S368 phosphorylation was reversed by the protein kinase C inhibitor chelerythrine. Raised [Ca2+]i also decreased I1 phosphorylation, also prevented by calcineurin inhibitors, to increase activity of the Ca2+-independent phosphatase, PPI. The PP1 inhibitor, tautomycin, prevented Cx43-365 dephosphorylation, Cx43-S368 phosphorylation and Gj reduction in raised [Ca2+]i. PP2A had no role. Conduction velocity was reduced by raised [Ca2+]i and reversed by calcineurin inhibitors. Reduced action potential conduction and Gj in raised [Ca2+] are regulated by calcineurin-dependent Cx43-S365 phosphorylation, leading to Cx43-S368 dephosphorylation. The calcineurin action is indirect, via I1 dephosphorylation and subsequent activation of PP1.

Cool AR, Bardswell SC, Pretheshan S, Dighe K, Kanaganayagam GS, Jabr RI, Merkle S, Marber MS, Engelhardt S, Avkiran M (2009) Paradoxical resistance to myocardial ischemia and age-related cardiomyopathy in NHE1 transgenic mice: A role for ER stress?, J MOL CELL CARDIOL 46 (2) pp. 225-233 ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD
Sarcolemmal Na+/H+ exchanger (NHE) activity, which is provided by the NHE isoform I (NHE1), has been implicated in ischemia/reperfusion-induced myocardial injury in animal models and humans, on the basis of studies with pharmacological NHE1 inhibitors. We generated a transgenic (TG) mouse model with cardiac-specific over-expression of NHE1 to determine whether this would be sufficient to increase myocardial susceptibility to ischemia/reperfusion-induced injury. TG mouse hearts exhibited increased sarcolemmal NHE activity and normal morphology and function. Surprisingly, they also showed reduced susceptibility to ischemia/reperfusion-induced injury as reflected by improved functional recovery and smaller infarcts. Such protection was sustained in the presence of NHE1 inhibition with zoniporide, indicating a mechanism that is independent of sarcolemmal NHE activity. Immunoblot analysis revealed accumulation of immature NHE1 protein as well as marked upregulation of both cytoprotective (78/94 kDa glucose-regulated proteins, calreticulin, protein disulfide isomerase) and pro-apoptotic (C/EBP homologous protein) components of the endoplasmic reticulum (ER) stress response in TG myocardium. With increasing age, NHE1 TG mice exhibited increased myocyte apoptosis, developed left ventricular contractile dysfunction, underwent cardiac remodelling and died prematurely. Our findings indicate that: (1) Cardiac-specific NHE1 over-expression induces the ER stress response in mouse myrocardium, which may afford protection against ischemia/reperfusion-induced injury despite increased NHE activity; (2) Ageing NHE1 TG mice exhibit myocyte apoptosis, cardiac remodelling and failure, likely as a result of Sustained ER stress; (3) The pluripotent effects of the ER stress response may confound studies that are based on the chronic over-expression of complex proteins in myrocardium. (C) 2008 Elsevier Inc. All rights reserved.
Dhillon PS, Chowdhury RA, Patel PM, Jabr R, Momin AU, Vecht J, Gray R, Shipolini A, Fry CH, Peters NS (2014) Relationship between connexin expression and gap-junction resistivity in human atrial myocardium,Circulation: Arrhythmia and Electrophysiology 7 (2) pp. 321-329
Background-The relative roles of the gap-junctional proteins connexin40 (Cx40) and connexin43 (Cx43) in determining human atrial myocardial resistivity is unknown. In addressing the hypothesis that changing relative expression of Cx40 and Cx43 underlies an increase in human atrial myocardial resistivity with age, this relationship was investigated by direct ex vivo measurement of gap-junctional resistivity and quantitative connexin immunoblotting and immunohistochemistry. Methods and Results-Oil-gap impedance measurements were performed to determine resistivity of the intracellular pathway (Ri), which correlated with total Cx40 quantification by Western blotting (rs=0.64, P
Fry CH, Sadananda P, Wood DN, Thiruchelvam N, Jabr RI, Clayton R (2011) Modeling the urinary tract-computational, physical, and biological methods.,Neurourol Urodyn 30 (5) pp. 692-699 Wiley
Models of the lower urinary tract are used to understand better the physiological and pathological functions of the tract and to gain insight into the relative importance of different components. The key requirement of a model is described, namely: to involve a continuous iteration with experiment; whereby experiments provide parameters and validation for components of the model, which is then used to generate hypotheses, which are tested experimentally. Different types of models are described: computational models that describe mathematically the whole urinary tract or components; physical models useful especially in testing medical devices; and tissue-engineered models. The purpose of modeling is first described in terms of the ability of models to predict the properties of the system of interest, using components that have a physiological interpretation, and to gain insight into the relative importance of different components. Examples are used to illustrate the use of modeling the urinary tract with reference to the different categories listed above. Neurourol. Urodynam. Neurourol. Urodynam. 30:692-699, 2011. © 2011 Wiley-Liss, Inc.
Wyndaele JJ, Gammie A, Bruschini H, De Wachter S, Fry CH, Jabr RI, Kirschner-Hermanns R, Madersbacher H (2011) Bladder compliance what does it represent: Can we measure it, and is it clinically relevant?, Neurourology and Urodynamics 30 (5) pp. 714-722
Aims: To report the conclusion of the Think Thank 8 on Compliance Discussions during the second ICI-RS meeting in 2010. Methods: During a 3-day meeting a group of specialists discussed bladder compliance, what it represents, how it can be measured and if it is clinically relevant. Results: Bladder compliance is the result of a mathematical calculation of the volume required for a unit rise of pressure measured during a cystometric filling. It gives an indication on how the different mechanisms in the bladder wall react on stretching. There is a need of standardization of measurement and suggestions for this are given in the text. Pitfalls are described and how to avoid them. There is a wide range of compliance values in healthy volunteers and groups of patients. Poor compliance needs to be defined better as it can have significant clinical consequences. Prevention and treatment are discussed. Conclusion: If compliance is correctly measured and interpreted, it has importance in urodynamic testing and gives information relevant for clinical management. © 2011 Wiley-Liss, Inc.
Gorog DA, Jabr RI, Tanno M, Sarafraz N, Clark JE, Fisher SG, Cao XB, Bellahcene M, Dighe K, Kabir AMN, Quinlan RA, Kato K, Gaestel M, Marber MS, Heads RJ (2009) MAPKAPK-2 modulates p38-MAPK localization and small heat shock protein phosphorylation but does not mediate the injury associated with p38-MAPK activation during myocardial ischemia, CELL STRESS CHAPERON 14 (5) pp. 477-489 SPRINGER
MAPKAPK-2 (MK2) is a protein kinase activated downstream of p38-MAPK which phosphorylates the small heat shock proteins HSP27 and alpha B crystallin and modulates p38-MAPK cellular distribution. p38-MAPK activation is thought to contribute to myocardial ischemic injury; therefore, we investigated MK2 effects on ischemic injury and p38 cellular localization using MK2-deficient mice (KO). Immunoblotting of extracts from Langendorff-perfused hearts subjected to aerobic perfusion or global ischemia or reperfusion showed that the total and phosphorylated p38 levels were significantly lower in MK2(-/-) compared to MK2(+/+) hearts at baseline, but the ratio of phosphorylated/total p38 was similar. These results were confirmed by cellular fractionation and immunoblotting for both cytosolic and nuclear compartments. Furthermore, HSP27 and alpha B crsytallin phosphorylation were reduced to baseline in MK2(-/-) hearts. On semiquantitative immunofluorescence laser confocal microscopy of hearts during aerobic perfusion, the mean total p38 fluorescence was significantly higher in the nuclear compared to extranuclear (cytoplasmic, sarcomeric, and sarcolemmal compartments) in MK2(+/+) hearts. However, although the increase in phosphorylated p38 fluorescence intensity in all compartments following ischemia in MK2(+/+) hearts was lost in MK2(-/-) hearts, it was basally elevated in nuclei of MK2(-/-) hearts and was similar to that seen during ischemia in MK2(+/+) hearts. Despite these differences, similar infarct volumes were recorded in wild-type MK2(+/+) and MK2(-/-) hearts, which were decreased by the p38 inhibitor SB203580 (1 mu M) in both genotypes. In conclusion, p38 MAPK-induced myocardial ischemic injury is not modulated by MK2. However, the absence of MK2 perturbs the cellular distribution of p38. The preserved nuclear distribution of active p38 MAPK in MK2(-/-) hearts and the conserved response to SB203580 suggests that activation of p38 MAPK may contribute to injury independently of MK2.
Pakzad M, Ikeda Y, McCarthy C, Kitney D, Jabr R, Fry CH (2016) Contractile effects and receptor analysis of adenosine-receptors in human detrusor muscle from stable and neuropathic bladders,Naunyn-Schmiedeberg's Archives of Pharmacology 389 (8) pp. 921-929 Springer
To measure the relative transcription of adenosine receptor subtypes and the contractile effects of adenosine and selective receptor-subtype ligands on detrusor smooth muscle from patients with neuropathic overactive (NDO) and stable bladders and also from guinea-pigs. Contractile function was measured at 37°C in vitro from detrusor smooth muscle strips. Contractions were elicited by superfusate agonists or by electrical field stimulation. Adenosine-receptor (A1, A2A, A2B, A3) transcription was measured by RT-PCR. Adenosine attenuated nerve-mediated responses with equivalent efficacy in human and guinea-pig tissue (pIC50 3.65?3.86); the action was more effective at low (1?8 Hz) compared to high (20? 40 Hz) stimulation frequencies in human NDO and guinea-pig tissue. With guinea-pig detrusor the action of adenosine was mirrored by the A1/A2-agonist N-ethylcarboxamido adenosine (NECA), partly abolished in turn by the A2B-selectve antagonist alloxazine, as well as the A1-selective agonist N6- cyclopentyladenosine (CPA). With detrusor from stable human bladders the effects of NECA and CPA were much smaller than that of adenosine. Adenosine also attenuated carbachol contractures, but mirrored by NECA (in turn blocked by alloxazine) only in guinea-pig tissue. Adenosine receptor subtype transcription was measured in human detrusor and was similar in both groups, except reduced A2A levels in overactive bladder. Suppression of the carbachol contracture in human detrusor is independent of A-receptor activation, in contrast to an A2B-dependent action with guinea-pig tissue. Adenosine also reduced nerve-mediated contractions, by an A1- dependent action suppressing ATP neurotransmitter action.
Kitney D, Jabr R, Vahabi B, Fry C (2017) Mild external heating and reduction in spontaneous contractions of the bladder,BJU International 120 (5) pp. 724-730 Wiley
To measure the effect of external heating on bladder wall
contractile function, histological structure and expression of
proteins related to tissue protection and apoptosis.
Material and Methods
In vitro preparations of bladder wall and ex vivo perfused pig
bladders were heated from 37 to 42°C, 46 and 50°C for
15 min. Isolated preparations were heated by radiant energy
and perfused bladders were heated by altering perfusate
temperature. Spontaneous contractions or pressure variations
were recorded, as well as responses to the muscarinic agonist
carbachol or motor nerve excitation in vitro during heating.
Tissue histology in control and after heating was analysed
using haematoxylin and eosin staining and 40-6-diamidino-2-
phenylindole (DAPI) nuclear labelling. The effects of heating
on protein expression levels of (i) heat shock proteins HSP27-
pSer82 and inducible-HSP70 and (ii) caspase-3 and its
downstream DNA-repair substrate poly-[ADP-ribose]
polymerase (PARP) were measured.
Heating to 42°C reduced spontaneous contractions or
pressure variations by ~70%; effects were fully reversible.
There were no effects on carbachol or nerve-mediated
responses. Tissue histology was unaffected by heating, and
expression of heat shock proteins as well as caspase-3 and
PARP were also unaltered. A TRPV1 antagonist had no
effect on the reduction of spontaneous activity. Heating to
46°C had a similar effect on spontaneous activity and also
reduced the carbachol contracture. Urothelial structure was
damaged, caspase-3 levels were increased and inducible-
HSP70 levels declined. At 50°C evoked contractions were
abolished, the urothelium was absent and heat shock
proteins and PARP expression was reduced with raised
caspase-3 expression.
Heating to 42°C caused a profound, reversible and
reproducible attenuation of spontaneous activity, with no
tissue damage and no initiation of apoptosis pathways.
Higher temperatures caused tissue damage and activation of
apoptotic mechanisms. Mild heating offers a novel approach
to reducing bladder spontaneous activity.
Henslee Erin, Crosby Priya, Kitcatt Stephen, Parry Jack S. W., Bernardini Andrea, Abdallat Rula G., Braun Gabriella, Fatoyinbo Henry O., Harrison Esther J., Edgar Rachel S., Hoettges Kai, Reddy Akhilesh B., Jabr Rita, von Schantz Malcolm, O?Neill John S., Labeed Fatima (2017) Rhythmic potassium transport regulates the circadian clock in human red blood cells,Nature Communications 8 1978(2017) Nature Publishing Group
Circadian rhythms organize many aspects of cell biology and physiology to a daily temporal program that depends on clock gene expression cycles in most mammalian cell types. However, circadian rhythms are also observed in isolated mammalian red blood cells (RBCs), which lack nuclei, suggesting the existence of post-translational cellular clock mechanisms in these cells. By using electrophysiological and pharmacological approaches, we show that human RBCs display circadian regulation of membrane conductance and cytoplasmic conductivity that depends on the cycling of cytoplasmic K+ levels. Using pharmacological intervention and ion replacement, we show that inhibition of K+ transport abolishes RBC electrophysiological rhythms. Our results suggest that in the absence of conventional transcription cycles, RBCs maintain a circadian rhythm in membrane electrophysiology through dynamic regulation of K+ transport.
Beale Andrew D., Kruchek Emily, Kitcatt Stephen J., Henslee Erin A., Parry Jack S.W., Braun Gabriella, Jabr Rita, von Schantz Malcolm, O?Neill John S., Labeed Fatima H. (2019) Casein kinase 1 underlies temperature compensation of circadian rhythms in human red blood cells,Journal of Biological Rhythms SAGE Publications
Temperature compensation and period determination by casein kinase 1 (CK1) are conserved features of eukaryotic circadian rhythms, whereas the clock gene transcription factors that facilitate daily gene expression rhythms differ between phylogenetic kingdoms. Human red blood cells (RBCs) exhibit temperature compensated circadian rhythms which, since RBCs lack nuclei, must occur in the absence of a circadian transcription-translation feedback loop. We tested whether period determination and temperature compensation are dependent on casein kinases in RBCs. As with nucleated cell types, broad spectrum kinase inhibition with staurosporine lengthened the period of the RBC clock at 37°C, with more specific inhibition of CK1 and CK2 also eliciting robust changes in circadian period. Strikingly, inhibition of CK1 abolished temperature compensation and increased the Q10 for the period of oscillation in RBCs, similar to observations in nucleated cells. This indicates that CK1 activity is essential for circadian rhythms irrespective of the presence or absence of clock gene expression cycles.
McCarthy Carly J., Ikeda Youko, Skennerton Deborah, Chakrabarty Basu, Kanai Anthony J., Jabr Rita I., Fry Christopher H. (2019) Characterisation of nerve?mediated ATP release from detrusor muscle; pathological implications,British Journal of Pharmacology Wiley

Background and Purpose.

To characterise the molecular mechanisms that determine variability of atropine?resistance of nerve?mediated contractions in human and guinea?pig detrusor smooth muscle

Experimental Approach.

Atropine?resistance of nerve?mediated contractions, and the role of P2X1 receptors, was measured in isolated preparations from guinea?pigs and also humans with or without overactive bladder syndrome, from which the mucosa was removed. Nerve?mediated ATP release was measured directly with amperometric ATP?sensitive electrodes. Ecto?ATPase activity of guinea?pig and human detrusor samples was measured in vitro by measuring the concentration?dependent rate of ATP breakdown. The transcription of ecto?ATPase subtypes in human samples was measured by qPCR.

Key Results

Atropine resistance was greatest in guinea?pig detrusor, absent in human tissue from normally?functioning bladders and intermediate in human overactive bladder. Greater atropine resistance correlated with reduction of contractions by the ATP?diphospho?hydrolase apyrase, directly implicating ATP in their generation. E?NTPDase?1 was the most abundantly transcribed ecto?ATPase of those tested and transcription was reduced in tissue from human overactive, compared to normal, bladders. E?NTPDase?1 enzymatic activity was inversely related to the magnitude of atropine resistance. Nerve?mediated ATP release was continually measured and varied with stimulation frequency over the range 1?16 Hz.

Conclusion and Implications

Atropine?resistance in nerve?mediated detrusor contractions is due to ATP release and its magnitude is inversely related to E?NTPDase?1 activity. ATP is released under different stimulation conditions compared to acetylcholine that implies different routes for their release

Henslee Erin A., Torcal Serrano Ruth M., Labeed Fatima H., Jabr Rita I., Fry Christopher H., Hughes Michael P., Hoettges Kai F. (2016) Accurate quantification of apoptosis progression and toxicity using a dielectrophoretic approach,The Analyst 141 (23) pp. 6408-6415 Royal Society of Chemistry
A loss of ability of cells to undergo apoptosis (programmed cell death, whereby the cell ceases to function and destroys itself) is commonly associated with cancer, and many anti-cancer interventions aim to restart the process. Consequently, the accurate quantification of apoptosis is essential in understanding the function and performance of new anti-cancer drugs. Dielectrophoresis has previously been demonstrated to detect apoptosis more rapidly than other methods, and is low-cost, label-free and rapid, but has previously been unable to accurately quantify cells through the apoptotic process because cells in late apoptosis disintegrate, making cell tracking impossible. In this paper we use a novel method based on light absorbance and multi-population tracking to quantify the progress of apoptosis, benchmarking against conventional assays including MTT, trypan blue and Annexin-V. Analyses are performed on suspension and adherent cells, and using two apoptosis-inducing agents. IC50 measurements compared favourably to MTT and were superior to trypan blue, whilst also detecting apoptotic progression faster than Annexin-V.
Beale Andrew D., Kruchek Emily, Kitcatt Stephen J., Henslee Erin A., Parry Jack S.W., Braun Gabriella, Jabr Rita, von Schantz Malcolm, O?Neill John S., Labeed Fatima (2019) Casein Kinase 1 Underlies Temperature Compensation of Circadian Rhythms in Human Red Blood Cells,Journal of Biological Rhythms 34 (2) pp. 144-153 SAGE Publications
Temperature compensation and period determination by casein kinase 1 (CK1) are conserved features of eukaryotic circadian rhythms, whereas the clock gene transcription factors that facilitate daily gene expression rhythms differ between phylogenetic kingdoms. Human red blood cells (RBCs) exhibit temperature-compensated circadian rhythms, which, because RBCs lack nuclei, must occur in the absence of a circadian transcription-translation feedback loop. We tested whether period determination and temperature compensation are dependent on CKs in RBCs. As with nucleated cell types, broad-spectrum kinase inhibition with staurosporine lengthened the period of the RBC clock at 37°C, with more specific inhibition of CK1 and CK2 also eliciting robust changes in circadian period. Strikingly, inhibition of CK1 abolished temperature compensation and increased the Q10 for the period of oscillation in RBCs, similar to observations in nucleated cells. This indicates that CK1 activity is essential for circadian rhythms irrespective of the presence or absence of clock gene expression cycles.
Hoettges Kai, Henslee Erin, Torcal Serrano Ruth M., Jabr Rita, Abdallat Rula, Beale Andrew, Waheed Abdul, Camelliti Patrizia, Fry Christopher, Van Der Veen Daan, Labeed Fatima, Hughes Michael (2019) Ten?Second Electrophysiology: Evaluation of the 3DEP Platform for high-speed, high-accuracy cell analysis.,Scientific Reports 9 19153 Nature Research
Electrical correlates of the physiological state of a cell, such as membrane conductance and capacitance, as well as cytoplasm conductivity, contain vital information about cellular function, ion transport across the membrane, and propagation of electrical signals. They are, however, difficult to measure; gold-standard techniques are typically unable to measure more than a few cells per day, making widespread adoption difficult and limiting statistical reproducibility. We have developed a dielectrophoretic platform using a disposable 3D electrode geometry that accurately (r2 > 0.99) measures mean electrical properties of populations of ~20,000 cells, by taking parallel ensemble measurements of cells at 20 frequencies up to 45 MHz, in (typically) ten seconds. This allows acquisition of ultra-high-resolution (100-point) DEP spectra in under two minutes. Data acquired from a wide range of cells ? from platelets to large cardiac cells - benchmark well with patch-clamp-data. These advantages are collectively demonstrated in a longitudinal (same-animal) study of rapidly-changing phenomena such as ultradian (2?3 hour) rhythmicity in whole blood samples of the common vole (Microtus arvalis), taken from 10 µl tail-nick blood samples and avoiding sacrifice of the animal that is typically required in these studies.

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