Abstract
The model of the interaction between Na and alanine at the mucosal border of rabbit ileum has been tested further by examining the efflux of alanine from the cells toward the mucosal solution. Alanine efflux shows a tendency toward saturation as cellular alanine concentration increases and is influenced by cellular Na concentration. A decrease in cell Na concentration causes an increase in the apparent Michaelis constant with little change in maximal efflux rate. Studies on strips of mucosa treated with ouabain or cyanide showed that the direction of net alanine transfer between the cells and the medium is determined by the direction of the Na concentration difference. The cells extrude alanine against a concentration difference when cell [Na] exceeds medium [Na] and accumulate alanine when cell [Na] is less than medium [Na]. The observations are consistent with the model previously suggested involving a transport site that combines with and translocates both Na and alanine, and with the concept that the Na concentration difference between mucosal solution and cytoplasm provides at least part of the energy for active transport of alanine.
Highlights
The model of the interaction between Na and alanine at the mucosal border of rabbit ileum has been tested further by examining the efflux of alanine from the cells toward the mucosal solution
The energy required to transport the amino acid into the cell across the mucosal border against a concentration difference is provided by the Na concentration difference between the cytoplasm and the mucosal solution
The results of a typical experiment on alanine efflux are shown in Fig. 1 in which log of the fraction of activity remaining in the mucosa is plotted against time of exposure to unlabeled solution
Summary
The model of the interaction between Na and alanine at the mucosal border of rabbit ileum has been tested further by examining the efflux of alanine from the cells toward the mucosal solution. In a series of earlier studies, certain aspects of the interaction between Na and alanine transport in rabbit ileum (1-4) were examined in some detail Those studies dealt mainly with the unidirectional influxes of Na and alanine across the brush border from the mucosal solution into the cells. THE JOURNAL OF GENERAL PHYSIOLOGY ·VOLUME 55 1970 servations were at least consistent with a mechanism for active transport of amino acid similar to the "Na gradient hypothesis" suggested by Crane (5) to account for sugar transport by intestine According to this hypothesis, the energy required to transport the amino acid into the cell across the mucosal border against a concentration difference is provided by the Na concentration difference between the cytoplasm and the mucosal solution. The present experiments represent an attempt to test some of these predictions
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