Membrane potential of squid axons: effect of internal and external ion concentration.

Transmembrane resting potentials of squid axons were measured with variation of intracellular salt concentrations. It was found that the dependence of resting potential on the extracellular K-ion concentration was practically unaffected by the change of ionic strength in the intracellular phase, and the relationship of membrane potential and the logarithm of extracellular K-ion concentration was a straight line with a slope of about 50 mV/10-fold extracellular K-ion concentration. Also, the degree of change in resting potential due to the change of intracellular K-ion concentration was not affected appreciably by the extracellular solution with various K-ion concentrations, and the membrane potentials were insensitive over a wide range of intracellular K-ion concentrations. It was also indicated that the observed transmembrane potentials are not explained by a conventional membrane potential theory.