Effect of starvation on neutral amino acid transport in isolated small-intestinal cells from guinea pigs.

The effects of starvation on neutral amino acid transport were examined in isolated enterocytes. Starvation stimulated L-alanine transport by the Na(+)-dependent system A and the Na(+)-independent system L without producing any changes in either the Na(+)-dependent systems ASC or the passive non-mediated uptake. Starvation produces a twofold increase in Vmax of system A without any change in Kt. Starvation produces an increase in Vmax of system L of 1.7 times without any change in Kt. Activation of systems A and L by starvation was reversible with subsequent refeeding. The effects of a series of amino acids on systems A and L were evaluated. A different inhibition pattern was found in starved animals as compared to controls. Starvation increases Na(+)-dependent L-alanine uptake and Na(+)-independent cycloleucine uptake by small-intestinal brush-border membrane vesicles. These results suggest that starvation stimulates amino acid transport across the apical plasma membrane of the enterocytes by inducing specific carrier units.