Relation between sodium-coupled amino acid and sugar transport and sodium/potassium pump activity in isolated...

Cells isolated from the epithelium of the small intestine are used to study the relationship between amino acid or sugar-coupled sodium transport and potassium uptake through the sodium/potassium pump. Potassium influx is a saturable function of the external potassium concentration. Uptake in the presence of ouabain, a specific pump inhibitor, is greatly reduced. This remaining influx is linearly related to the concentration up to 6 mM potassium. Sugars and amino acids are actively accumulated by the intestinal cells. Their transport is accompanied by an initial extra influx of sodium. Although cells seem to regulate their internal sodium concentrations, this is not accompanied with a concomitant increase in potassium uptake through the pump. Thus L-alanine, 3-0-methyl-D-glucoside, and alpha-methyl-D-glucoside all fail to increase the rate of ouabain-sensitive potassium uptake. A very high coupling ratio of sodium efflux to potassium influx through the pump would be a likely explanation of the present results though they cannot be regarded as conclusive.