Tracer and Nontracer Potassium Fluxes in Squid Giant Axons and the Effects of Changes in External Potassium Concentration and Membrane Potential

Abstract

The efflux of labeled unlabeled potassium ions from the squid giant axon has been measered under a variety of experimental conditions. Axons soaked in sea water containing K42 ions lost radioactivity when placed in inactive sea water according to kinetics which indicate the presence of at least two cellular compartments. A rapdily equilibrating superficial compartment, probably the Schwann cell, was observed to elevate the specific activity of K42 lost from such axons to K-free sea water for a period of hours. The extra radioactive potassium loss from such axons during stimulation, however, was shown to have a specific activity identical within error to that measured in the xaoplasm at the end of the experiment. The same was shown for the extra potassium loss occurring during passage of a steady depolarizing current. Axons placed in sea water with an elevated potassium ion concentration (50 m[image]) showed an increased potassium efflux that was in general agreement with the accompanying increase in membrane conductance. The efflux of potassium ions observed in 50 m[image] K sea water at different membrane potentials did not support the theory that the potassium fluxes obey the independence principle.