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  • Title: Effects of R-56865 on transient inward current, Na(+)-Ca2+ exchange, and Ca2+ release from SR in cardiac myocytes.
    Author: Ichikawa H, Hearse DJ, Coetzee WA.
    Journal: Am J Physiol; 1994 Feb; 266(2 Pt 2):H511-20. PubMed ID: 8141352.
    Abstract:
    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.
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