External potassium and the membrane potential of single muscle fibers.

Abstract

ONE important supporting fact for the concept of the membrane potential of muscle and nerve being a diffusion potential1 was the demonstration of a rectilinear relationship between the logarithm of the external potassium concentration and the measured membrane potential, according to the Nernst equation: This was shown to be approximately true by Cowan2 for the injury potential of crab nerve and by Shanes3 for the ‘anaerobic’ fraction of the injury potential of frog nerve. Doubts as to the significance of the rectilinearity of their curves4,5 seem to be met, at least in the case of squid giant axon, by the work of Curtis and Cole6, although these authors hesitated to ascribe the membrane potential completely to the potassium concentration gradient. Using the classical injury potential technique, a similar relationship has been demonstrated in frog muscles by Steinbach7 and by Boyle, Conway and co-workers8,9. Thus a potential v. log [K+] relation has been found for both nerve and muscle.