Effects of sodium extrusion and local anaesthetics on muscle membrane resistance and potential

Abstract

Membrane potentials and resistances of K-depleted muscles were measured in the cold and again after warming in K-containing media so that active ion movements occurred. On warming there was a fall of resistance and a gradual rise of potential which passed through a maximum. Later measurements of resistance in a chloride medium showed that values were, if anything, higher than initially in the warm. The excess potentials measured approximated to those required to induce passive inward movement of the K ions through the measured K resistance. Permeabilities for K+ and Cl- were deduced. When cocaine, procaine, amytal or mepyramine were added or when K+ was replaced by Rb+ in the Cl--free solution the K+ permeability was eventually reduced. The same agents led to an enhanced initial response of potential to warming, but later the potentials in Cl--free media fell to less than the K+ equilibrium values. A method for obtaining the resistivity of the membrane from measurements made in conditions of non-linear voltage-current dependence was applied.