Na Extrusion by the Sartorius of Rana pipiens.

Sartorius muscles of R. pipiens may be enriched in sodium and depleted of potassium by prolonged soaking in the cold in K-free or low K Ringer's solution. Such K-depleted muscles take up potassium and extrude sodium when exposed to Ringer's solution containing 10 mM K at ordinary room temperature (ca. 20 degrees C), with no dependence on external Na ion concentration in either phase within fairly wide limits. Extrusion of excess fiber Na is demonstrated on single muscles using Na(24)-loaded tissues. Rate of exchange of excess fiber Na does not differ significantly from the rate of exchange of Na normally present in muscle fibers.