Action potential duration-stabilizing action of taurine in guinea pig ventricular myocytes.
To examine taurine actions on the rate of repolarization of action potentials (AP), L-type Ca2+ (ICa), late outward K+ (Ik) and the inward rectifier currents as affected by the external Ca2+ concentrations ([Ca2+]o), whole-cell voltage-clamp and current-clamp experiments were conducted in guinea pig ventricular myocytes. At a high (3.6 mM) [Ca2+]o, 10 mM taurine suppressed both ICa and IK, shortened AP duration and decelerated the rate (-dV/dt) of terminal repolarization of AP. In contrast, at a low (0.9 mM) [Ca2+]o, taurine intensified both ICa and IK, lengthened AP duration and accelerated -dV/dt. However, at either [Ca2+]o, the resting membrane potential was slightly hyperpolarized, and the inward rectifier, current examined by the ramp-pulse protocol remained unaffected by taurine. Taurine is suggested to maintain a stable AP duration by altering the inward Ca2+ and IK in the opposite directions, depending on [Ca2+]o. The relevance of the stabilizing action of taurine on the AP duration to its reported anti-arrhythmic efficacies is discussed.
Sada
H
H
Department of Pharmacology, School of Medicine, Yamaguchi University, Ube, Japan.
Ban
T
T
Sperelakis
N
N
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D013654:Taurine / Q000494:pharmacology*; D016276:Ventricular Function
D007473:Ion Channels; D013654:Taurine; D011188:Potassium; D002118:Calcium