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The effects of external Ca2+ reduction on the biphasic potassium (K) contractures and the action of divalent cations under conditions of the Ca2+ reduction were examined in detail, using frog single twitch muscle fibers. The peak tension of the initial component of 80 mM K+ contractures was greatly potentiated by exposing the fiber to low Ca2+ solution for(More)
The time course of the inhibition of peak tension (inactivation) of potassium contracture induced by conditioning depolarization with 10, 15, 20 and 30 mM K+ was examined, using single twitch fibers from the frog semitendinosus muscle. The time-dependence curve of the inactivation was biphasic, consisting of the first phase and the second phase. The first(More)
When the concentration of external Ca2+ was reduced for 30 sec in a single twitch muscle fiber of a frog, the peak tension of the initial component of biphasic 80 mM K+ contractures was potentiated, whereas that of the secondary component was markedly inhibited, despite the fact that in the early stage it was potentiated usually in case of contractures in(More)
The dependence of the occurrence of biphasic contractures on potassium chloride concentration, and the activation curve, the inactivation curve and the time-dependence curve of inactivation of the initial component of potassium contracture and those curves of the secondary component were examined, using single twitch fibers of the frog semitendinosus(More)
The flexor carpi radialis muscle (FCRM) of the frog was divided into phasic and tonic bundles, and the properties of the potassium contracture in the tonic bundle were examined. The potassium contracture was tonic and the contracture induced by K higher than 75 mM consisted of the initial phasic component and of the following sustained component. Both(More)
The characteristics and the mechanism of the biphasic potassium contractures, i.e., an initial rapid contraction (initial component) and a slow secondary contraction (secondary component) were investigated in detail using single twitch fibers from the semitendinosus muscles of the frog, Rana japonica. The present experiments confirmed the results of(More)
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