Exchange of Electrolytes in Smooth Muscle

Abstract

Exchange of electrolytes, particularly that of potassium, was studied in the smooth muscle of the frog's stomach by chemical analysis and by following the release of K⁴² from muscles previously equilibrated with tracer. The muscles exchanged about 4% of their potassium rapidly. After about 20 minutes the washout curves became exponential. Muscles previously washed in 2 mm CaCl₂ for 1 hour were able to retain about 80% of the potassium normally present, although the fibers were freely permeable to sodium and potassium. Exchange of potassium in such muscles was slowed by the presence of low concentrations of calcium. The results suggest that the slowness of exchange is not due to a surface membrane, but due to adsorption of a large part of the intracellular potassium.