Active Secretion of Sodium Ions from Isolated Sodium-rich Skeletal Muscle

Abstract

THE isolated sartorius of the frog, when immersed in Ringer fluid with normal potassium content, loses potassium and gains sodium rather rapidly at room temperature¹. This also occurs at 0° C., but at a slower rate, the gain of sodium being greater when potassium-free Ringer is used². When this potassium-free Ringer fluid has the same average inorganic composition as frog plasma¹ with a sodium content of 104 mM, the change in muscle sodium overnight is from its normal content of 24 m.equiv./kgm. to 47 m.equiv./kgm. (the average change in weight being only −1.2 per cent). If companion muscles are similarly treated and then immersed at room temperature for 2 hr. in similar fluid containing 10 m.equiv. potassium/litre, but the same concentration of sodium, there is no appreciable excretion of sodium. Steinbach's conclusions³ to the contrary have been shown to depend very largely, if not altogether, on a faulty statistical procedure.