EFFECTS OF SODIUM DEPLETION ON THE CAFFEINE-INDUCED CONTRACTION OF FROGS 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°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 for 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°C. The apparent discrepancy between these two conditions is discussed. © 1990, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.