Effects of sodium depletion on the caffeine-induced contraction of frog's skeletal muscle.
Effects of depletion of Na ions from the environmental medium on the caffeine-induced contraction were investigated in both intact and skinned fibers prepared from the frog's fast twitch muscle. In intact muscle fibers, both the twitch and the contracture induced by 5 mM caffeine were enhanced by depleting the external Na at 9-10 degrees C. In contrast, in the mechanically skinned muscle fiber, which was used to examine the capability of the sarcoplasmic reticulum to take up Ca ions from the sarcoplasm and/or the superfusing medium, the contractile tension as well as its fractional area measured by applying 25 mM caffeine were markedly inhibited by Na-depletion at 5 degrees C. The apparent discrepancy between these two conditions is discussed.
Department of Physiology, School of Medicine, Fukuoka University, Japan.
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H
Kawata
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Fujishiro
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D007474:Ion Exchange; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D011898:Ranidae; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*
D002110:Caffeine; D012964:Sodium; D002118:Calcium