title: Ionic mechanisms underlying action potential prolongation by focal cerebral ischemia in rat ventricular myocytes.
abstract: Despite prolongation of the QTc interval in humans during cerebral ischemia, little is known about the mechanisms that underlie these actions. Cerebral ischemic model was established by middle cerebral artery occlusion (MCAO) for 24 h. In rat ventricular myocytes, the effect of cerebral ischemia on action potential duration (APD) and underlying electrophysiologic mechanisms were investigated by whole-cell patch clamp. We demonstrated that heart rate-corrected QT interval and APD were prolonged with frequent occurrence of ventricular tachyarrhythmias in a rat model of MCAO. The I(Na) density was overall smaller in cerebral ischemic myocytes relative to sham myocytes (P < 0.01). The Nav1.5 protein and mRNA levels (pore-forming subunit for I(Na) ) were decreased by about 20% (P < 0.01) in cerebral ischemic rat hearts than those in sham-operated rat hearts. Peak transient outward K(+) current (I(to)) at +60 mV was found decreased by approximately 32.3% (P < 0.01) in cerebral ischemic rats. The peak amplitude of L-type Ca(2+) current (I(Ca,L)) was increased and the inactivation kinetics were slowed (P < 0.01). Protein level of the pore-forming subunit for I(to) was decreased, but that for I(Ca,L) was increased. The inward rectifier K(+) current (I(K1)) at -120 mV and its protein level were unaffected. Our study represents the first documentation of I(Na), I(to) and I(Ca,L) channelopathy as the major ionic mechanism for cerebral ischemic QT prolongation.
authors.affiliation: Department of Pharmacology, State-Province Key Laboratory of China, Heilongjiang, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Wang
authors.forename: Lihua
authors.initials: L
authors.lastname: Sun
authors.forename: Yanli
authors.initials: Y
authors.lastname: Zhang
authors.forename: Huiwei
authors.initials: H
authors.lastname: Wu
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Zhenwei
authors.initials: Z
authors.lastname: Pan
authors.forename: Yanjie
authors.initials: Y
authors.lastname: Lu
authors.forename: Baofeng
authors.initials: B
authors.lastname: Yang
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism / Q000503:physiopathology*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D004594:Electrophysiology; D006352:Heart Ventricles / Q000166:cytology; D020244:Infarction, Middle Cerebral Artery / Q000473:pathology; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D015221:Potassium Channels / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D062554:NAV1.5 Voltage-Gated Sodium Channel; D015221:Potassium Channels; D012333:RNA, Messenger; C568320:SCN5A protein, human; C568322:Scn5a protein, rat; D015222:Sodium Channels