Sodium-dependent amino acid transport by cultured hamster cells: membrane vesicles retain transport changes due to glucose starvation and cycloheximide.

Abstract

Enhanced .alpha.-aminoisobutyric acid transport by hamster [Nil strain fibroblasts] cells cultured in the absence of D-glucose was demonstrated in isolated membrane vesicles. The observed enhancement was seen in the presence but not in the absence of Na+. Kinetic analysis of transport using both the intact cells and the membrane vesicles showed that the overall enhancement was associated with an increase in Vmax. Decreases in transport activity by intact cells resulting from extended exposure of the cells to inhibitors of protein synthesis, such as cycloheximide, were also evident in membrane vesicles. The use of metabolically inactive membrane vesicles demonstrated that amino acid uptake by intact cells is a transport property of the plasma membrane. Membrane vesicle preparations can be exploited for the purpose of studying the regulation of amino acid transport. The data suggest that carrier turnover is involved in the regulation of amino acid transport in animal cells.