Oxygen consumption and Ca exchangeability at different levels of potassium depolarization were studied in frog sartorius muscle. It was found that the changes in oxygen consumption parallel the changes in Ca exchangeability. Procaine M) and CaClz (2.10-2 M ) suppressed both extra oxygen consumption and Ca exchangeability at low values of depolarization. At higher values of depolarization procaine and CaCls differed in their action. Procaine favored inhibition of these processes, CaCL caused their activation. The effects of these compounds was not a result of a change in the membrane potential, since their effect on potassium depolarization was found to be small. Relations between oxygen consumption and Ca exchangeability similar to those observed at potassium depolarization seem to exist under conditions where caffeine was applied. It is proposed that the extra oxygen consumption caused by potassium depolarization or on application of caffeine and unaccompanied by mechanical changes is related to the release of Ca from its bound form. Oxygen consumption in isotonic sucrose solution was also studied, but some different data from the above were obtained.
The effect of potassium depolarization on frog muscle has been the object of physiological studies for several decades. However, a detailed picture of electrical and mechanical changes in fast muscle fibers during potassium depolarization has only recently emerged from the studies of Adrian ('56) and Hodgkin and Horowicz ('60). Their results offered also a new basis for studies on relations between electrical and mechanical processes in frog muscle fibers on one hand and metabolic processes on the other hand. The exact mechanism of the relations between these processes in frog muscle is not known so far. Nevertheless, on the basis of the above mentioned studies and the works of other authors (Hegnauer, Fenn and Cobb, '34; Solandt, '36; Hill and Howarth, '57; Briner et al., '59; Muller and Simon, '60; dealing with metabolism in frog sartorius, the processes taking place in this muscle during potassium depolarization may be described as follows: If the membrane potential of frog sartorius fibers is reduced by high potassium depolarization to values lower than 50 mV, phasic contractures and a short-time increase in metabolism occur. If, however, the membrane potential is reduced only to values higher than 50 mV, a