Comparative study of latency relaxation and contraction of frog skeletal muscle (author's transl)

Abstract

Latency relaxation (LR) and contraction of frog skeletal muscle are compared with respect to their behavior on changes of temperature, low level activation by 1 mM caffeine and 15 mM K+ and calcium deprivation of extracellular medium. Temperature dependence of the amplitudes ofLR and contraction is different, whereas latency periods and rates of force development ofLR and contraction show identical temperature dependence, respectively. 1 mM caffeine increases contraction and decreasesLR. Besides a general decrease of both,LR and contraction in 15 mM K+ there is a specific diminution ofLR, as expressed by a shortening of latency period of contraction. In Ca++ deprived solution, in which Ca++ are substituted by an aquivalent quantity of Ni++,LR is relatively more reduced than contraction is. The experiments show, thatLR depends strongly on Ca++ concentration. The results are in accordance with the idea, theLR is caused by a change of elastic properties of intracellular structures of the muscle fibre; these structures might be “resting” cross bridges between the contractile filaments as well as longitudinal sarcoplasmic reticulum. This interpretation agrees with the findings of Hill (1968) and Lannergren (1971) on elastic behavior of skeletal muscle and single fibres of skeletal muscle.