External Potassium and the Membrane Potential of Single Muscle Fibres

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 curves^4,5 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-workers^8,9. Thus a potential v. log [K⁺] relation has been found for both nerve and muscle.