ACTION OF MANGANESE IONS ON EXCITATIONCONTRACTION COUPLING OF FROG SKELETAL MUSCLE FIBRES

Abstract

1. The action of manganese ions on excitation-contraction coupling in frog skeletal muscle fibres was studied.2. In normal Ringer's solution, twitch tension development was inhibited by the addition of 10 mM-Mn. The inhibitory effect of Mn on twitch tension development was not eliminated by addition of 1 mM caffeine.3. In 10 mM-Mn Ringer's solution, membrane potential of the semitendinosus muscle fibre was increased by 9.1 mV and the hyperpolarizing action of Mn was observed in various concentrations of potassium up to 50 mM.4. The action potential was still observed in 10 mM-Mn Ringer's solution and negative afterpotential was prolonged. In 10 mM-Mn Ringer's solution, an intensity of electrical current needed to elicit action potential was increased.5. Negative afterpotential which disappeared after glycerol treatment (HOWELL and JENDEN, 1967) could not be regained by treatment of 10 mM-Mn.6. Mn suppressed potassium contractures induced by 80 mM-K or less (constant [K]×[Cl] product). Removal of Mn from 50 mM-K Ringer's solution produced an unusual tension development. Tension development produced by Mn removal from 80 mM-K, 10 mM-Mn Ringer's solution was smaller than that produced by Mn removal from 50 mM-K, 10 mM-Mn Ringer's solution.7. Caffeine rapid cooling contracture was not affected in the presence of Mn. After the disruption of T-tubules produced by glycerol treatment, caffeine rapid cooling contracture was also observed even in the presence of Mn.8. No morphological changes in muscle fibres treated with Mn were recognized by electron microscopical studies.9. From these results it was considered that Mn acted on transverse tubules to inhibit the influx of Ca, but did not directly affect the sarcoplasmic reticulum.