title: Effects of L-type Ca2+ channel antagonism on ventricular arrhythmogenesis in murine hearts containing a modification in the Scn5a gene modelling human long QT syndrome 3.
abstract: Ventricular arrhythmogenesis in long QT 3 syndrome (LQT3) involves both triggered activity and re-entrant excitation arising from delayed ventricular repolarization. Effects of specific L-type Ca2+ channel antagonism were explored in a gain-of-function murine LQT3 model produced by a DeltaKPQ 1505-1507 deletion in the SCN5A gene. Monophasic action potentials (MAPs) were recorded from epicardial and endocardial surfaces of intact, Langendorff-perfused Scn5a+/Delta hearts. In untreated Scn5a+/Delta hearts, epicardial action potential duration at 90% repolarization (APD90) was 60.0 +/- 0.9 ms compared with 46.9 +/- 1.6 ms in untreated wild-type (WT) hearts (P < 0.05; n = 5). The corresponding endocardial APD(90) values were 52.0 +/- 0.7 ms and 53.7 +/- 1.6 ms in Scn5a+/Delta and WT hearts, respectively (P > 0.05; n = 5). Epicardial early afterdepolarizations (EADs), often accompanied by spontaneous ventricular tachycardia (VT), occurred in 100% of MAPs from Scn5a+/Delta but not in any WT hearts (n = 10). However, EAD occurrence was reduced to 62 +/- 7.1%, 44 +/- 9.7%, 10 +/- 10% and 0% of MAPs following perfusion with 10 nm, 100 nm, 300 nm and 1 mum nifedipine, respectively (P < 0.05; n = 5), giving an effective IC50 concentration of 79.3 nm. Programmed electrical stimulation (PES) induced VT in all five Scn5a+/Delta hearts (n = 5) but not in any WT hearts (n = 5). However, repeat PES induced VT in 3, 2, 2 and 0 out of 5 Scn5a+/Delta hearts following perfusion with 10 nm, 100 nm, 300 nm and 1 mum nifedipine, respectively. Patch clamp studies in isolated ventricular myocytes from Scn5a+/Delta and WT hearts confirmed that nifedipine (300 nm) completely suppressed the inward Ca2+ current but had no effect on inward Na+ currents. No significant effects were seen on epicardial APD90, endocardial APD90 or ventricular effective refractory period in Scn5a+/Delta and WT hearts following perfusion with nifedipine at 1 nm, 10 nm, 100 nm, 300 nm and 1 microm nifedipine concentrations. We conclude that L-type Ca2+ channel antagonism thus exerts specific anti-arrhythmic effects in Scn5a+/Delta hearts through suppression of EADs.
authors.affiliation: Section of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
authors.forename: Glyn
authors.initials: G
authors.lastname: Thomas
authors.forename: Iman S
authors.initials: IS
authors.lastname: Gurung
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Killeen
authors.forename: Parvez
authors.initials: P
authors.lastname: Hakim
authors.forename: Catharine A
authors.initials: CA
authors.lastname: Goddard
authors.forename: Martyn P
authors.initials: MP
authors.lastname: Mahaut-Smith
authors.forename: William H
authors.initials: WH
authors.lastname: Colledge
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 / Q000187:drug effects / Q000502:physiology; D000814:Aniline Compounds; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000188:drug therapy* / Q000235:genetics* / Q000503:physiopathology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D006352:Heart Ventricles / Q000187:drug effects / Q000503:physiopathology; D006801:Humans; D066298:In Vitro Techniques; D008133:Long QT Syndrome / Q000235:genetics* / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000187:drug effects; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D015222:Sodium Channels / Q000235:genetics*; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; C092068:Kcne1 protein, mouse; D062554:NAV1.5 Voltage-Gated Sodium Channel; D024642:Potassium Channels, Voltage-Gated; C568320:SCN5A protein, human; C568321:Scn5a protein, mouse; D015222:Sodium Channels; D014966:Xanthenes; C059715:Fluo-3; D009543:Nifedipine