title: Epac activation, altered calcium homeostasis and ventricular arrhythmogenesis in the murine heart.
abstract: The recently described exchange protein directly activated by cAMP (Epac) has been implicated in distinct protein kinase A-independent cellular signalling pathways. We investigated the role of Epac activation in adrenergically mediated ventricular arrhythmogenesis. In contrast to observations in control conditions (n = 20), monophasic action potentials recorded in 2 of 10 intrinsically beating and 5 of 20 extrinsically paced Langendorff-perfused wild-type murine hearts perfused with the Epac activator 8-pCPT-2'-O-Me-cAMP (8-CPT, 1 microM) showed spontaneous triggered activity. Three of 20 such extrinsically paced hearts showed spontaneous ventricular tachycardia (VT). Programmed electrical stimulation provoked VT in 10 of 20 similarly treated hearts (P < 0.001; n = 20). However, there were no statistically significant accompanying changes (P > 0.05) in left ventricular epicardial (40.7 +/- 1.2 versus 44.0 +/- 1.7 ms; n = 10) or endocardial action potential durations (APD(90); 51.8 +/- 2.3 versus 51.9 +/- 2.2 ms; n = 10), transmural (DeltaAPD(90)) (11.1 +/- 2.6 versus 7.9 +/- 2.8 ms; n = 10) or apico-basal repolarisation gradients, ventricular effective refractory periods (29.1 +/- 1.7 versus 31.2 +/- 2.4 ms in control and 8-CPT-treated hearts, respectively; n = 10) and APD(90) restitution characteristics. Nevertheless, fluorescence imaging of cytosolic Ca(2+) levels demonstrated abnormal Ca(2+) homeostasis in paced and resting isolated ventricular myocytes. Epac activation using isoproterenol in the presence of H-89 was also arrhythmogenic and similarly altered cellular Ca(2+) homeostasis. Epac-dependent effects were reduced by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibition with 1 microM KN-93. These findings associate VT in an intact cardiac preparation with altered cellular Ca(2+) homeostasis and Epac activation for the first time, in the absence of altered repolarisation gradients previously implicated in reentrant arrhythmias through a mechanism dependent on CaMKII activity.
authors.affiliation: University of Cambridge, Downing Street, Cambridge, CB2 3EG, UK. ssh26@cam.ac.uk
authors.forename: Sandeep S
authors.initials: SS
authors.lastname: Hothi
authors.forename: Iman S
authors.initials: IS
authors.lastname: Gurung
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Heathcote
authors.forename: Yanmin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Booth
authors.forename: Jeremy N
authors.initials: JN
authors.lastname: Skepper
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Grace
authors.forename: Christopher L-H
authors.initials: CL
authors.lastname: Huang
mesh_terms: D000200:Action Potentials; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D020662:Guanine Nucleotide Exchange Factors / Q000819:agonists / Q000378:metabolism*; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D006706:Homeostasis; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010477:Perfusion; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012032:Refractory Period, Electrophysiological; D013449:Sulfonamides / Q000494:pharmacology; D017180:Tachycardia, Ventricular / Q000378:metabolism* / Q000503:physiopathology; D013997:Time Factors; D000096926:Benzenesulfonamides
chemical_list: D000318:Adrenergic beta-Agonists; D001596:Benzylamines; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D000242:Cyclic AMP; D020662:Guanine Nucleotide Exchange Factors; D007545:Isoproterenol; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; C482601:Epac protein, mouse; C072105:KN 93; D000096926:Benzenesulfonamides; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide