Sorption of potassium in the small and the large intestine

Abstract

The effect of changes in concentration of K in luminal contents on its insorption, exsorption, and net sorption was determined in Thiry-Vella fistulas of upper jejunum, lower ileum, and proximal colon of healthy trained dogs. Twenty-five-mililiter samples of Tyrode solution modified to contain varying concentrations of K and kept isotonic by altering the Na content were instilled into the loops. Isotopically labeled Na, K, and water were added to the test solutions to determine unidirectional fluxes. The rate of insorption of K was dependent on its concentration in the luminal fluid but rate of exsorption was not. Net sorption was also concentration dependent. Potassium was always enterosorbed when its luminal concentration was equal to or less than that of blood and always absorbed at concentrations greater than that in blood. Small, negative, mucosal-blood potential differences at each site were independent of the K content of the luminal fluid. The data indicate that insorption of K at each site is passive. Active secretion may occur in the colon.