Effects of R-56865 on transient inward current, Na(+)-Ca2+ exchange, and Ca2+ release from SR in cardiac myocytes.
Voltage-clamp studies were performed on guinea pig ventricular myocytes to clarify the action of N-(1-[4-(4-fluorophenoxy)butyl]-4-piperidinyl)-N-methyl-2-benzothiazo lamine (R-56865), an inhibitor of cardiac glycoside-induced arrhythmias. Transient inward current ((Iti)) was induced using low-K+/high-Ca2+ Tyrode solution. R-56865 (1 mM) was found to abolish I(ti). R-56865 had no influence on the peak Ca2+ current, steady-state current during the clamp, holding current, or the Ni(2+)-sensitive electrogenic Na(+)-Ca2+ exchange current. Fluorescence transients after repolarization (temporally related to the I(ti)) were abolished by R-56865 without affecting the fluorescence transients during depolarization. In separate experiments, the threshold of Ca2+ release from sarcoplasmic reticulum (SR) by the Ca2+ current was found to be unchanged, whereas Ca2+ transients (presumably triggered by Ca2+ entry through the Na(+)-Ca2+ exchanger) were depressed. Our results suggest that R-56865 inhibits spontaneous Ca2+ release from the SR when it is mediated by Ca2+ entry through the Na(+)-Ca2+ exchanger but that it has no direct effect on the well-known "physiological" Ca(2+)-induced Ca(2+)-release mechanism from SR.
Ichikawa
H
H
Cardiovascular Research, Rayne Institute, St. Thomas' Hospital, London, United Kingdom.
Hearse
D J
DJ
Coetzee
W A
WA
D000818:Animals; D052160:Benzothiazoles; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D013844:Thiazoles / Q000494:pharmacology*; D013997:Time Factors
D052160:Benzothiazoles; D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D010880:Piperidines; D019831:Sodium-Calcium Exchanger; D013844:Thiazoles; C054551:R 56865; D012964:Sodium; D002118:Calcium