Effect of inhibitors on alanine transport in isolated rabbit ileum

The effects of metabolic inhibitors and ouabain on alanine transport across rabbit ileum, in vitro, have been investigated. Net transport of alanine and Na across short-circuited segments of ileum is virtually abolished by cyanide, 2,4-dinitrophenol, iodoacetate, and ouabain. However, these inhibitors do not markedly depress alanine influx from the mucosal solution, across the brush border, into the intestinal epithelium, and they do not significantly affect the Na dependence of this entry process. The results of this investigation indicate that: (a) the Na dependence of alanine influx does not reflect a mechanism in which the sole function of Na is to link metabolic energy directly to the influx process; and (b) the inhibition of net alanine transport across intestine is, in part, the result of an increased rate coefficient for alanine efflux out of the cell across the brush border. Although these findings do not exclude a direct link between metabolic energy and alanine efflux, the increased efflux may be the result of the increased intracellular Na concentration in the presence of these inhibitors. The results of these studies are qualitatively consistent with a model for alanine transport across the brush border which does not include a direct link to metabolic energy.