title: Action potential duration restitution and alternans in rabbit ventricular myocytes: the key role of intracellular calcium cycling.
abstract: Action potential duration (APD) restitution properties and repolarization alternans are thought to be important arrhythmogenic factors. We investigated the role of intracellular calcium (Ca2+i) cycling in regulating APD restitution slope and repolarization (APD) alternans in patch-clamped rabbit ventricular myocytes at 34 to 36 degrees C, using the perforated or ruptured patch clamp techniques with Fura-2-AM to record Ca2+i. When APD restitution was measured by either the standard extrastimulus (S1S2) method or the dynamic rapid pacing method, the maximum APD restitution slope exceeded 1 by both methods, but was more shallow with the dynamic method. These differences were associated with greater Ca2+i accumulation during dynamic pacing. The onset of APD alternans occurred at diastolic intervals at which the APD restitution slope was significantly <1 and was abolished by suppressing sarcoplasmic reticulum (SR) Ca2+i cycling with thapsigargin and ryanodine, or buffering the global Ca2+i transient with BAPTA-AM or BAPTA. Thapsigargin and ryanodine flattened APD restitution slope to <1 when measured by the dynamic method, but not by the S1S2 method. BAPTA-AM or BAPTA failed to flatten APD restitution slope to <1 by either method. In conclusion, APD alternans requires intact Ca2+i cycling and is not reliably predicted by APD restitution slope when Ca2+i cycling is suppressed. Ca2+i cycling may contribute to differences between APD restitution curves measured by S1S2 versus dynamic pacing protocols by inducing short-term memory effects related to pacing-dependent Ca2+i accumulation.
authors.affiliation: UCLA Cardiovascular Research Laboratory, Department of Medicine (Cardiology), David Geffen School of Medicine at UCLA, Los Angeles, Calif 90095-1679, USA. jgoldhaber@mednet.ucla.edu
authors.forename: Joshua I
authors.initials: JI
authors.lastname: Goldhaber
authors.forename: Lai-Hua
authors.initials: LH
authors.lastname: Xie
authors.forename: Tan
authors.initials: T
authors.lastname: Duong
authors.forename: Christi
authors.initials: C
authors.lastname: Motter
authors.forename: Kien
authors.initials: K
authors.lastname: Khuu
authors.forename: James N
authors.initials: JN
authors.lastname: Weiss
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D002304:Cardiac Pacing, Artificial; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006329:Heart Conduction System / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000503:physiopathology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D020746:Calcium Channels, L-Type; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D012433:Ryanodine; D002110:Caffeine; D004533:Egtazic Acid; D019284:Thapsigargin; D002118:Calcium