Sodium-amino acid interactions in the intestinal epithelium

Abstract

Much evidence has accumulated during the last few years to suggest a direct coupling between the movement of sodium and amino acids across plasma membranes, a sodium gradient providing energy for the active transport of amino acid. This work is summarized and attention drawn to instances where it seems unlikely that a sodium gradient can be the only driving force involved. An alanine dependent sodium influx and a sodium dependent alanine influx can be demonstrated to occur in intestinal epithelia. In the rabbit ileum these dependent fluxes are said to be coupled in a oneto-one fashion but, in the goldfish intestine, the ratio appears to depend on the external sodium concentration. The rate of potassium influx into the goldfish mucosa is approximately equal to that for sodium, but various attempts to demonstrate an alanine dependent potassium influx have failed. High concentrations of potassium inhibit the sodium—alanine interaction. These results with potassium are used to emphasize the specificity of the amino acid interaction for sodium.