Alanine transport in plasma membrane vesicles from Yoshida ascites hepatoma cells (AH 130) in the exponential and stationary phase of growth

Abstract

The Na(+)-dependent transport of L-alanine into plasma membrane vesicles from Yoshida ascites hepatoma (AH-130) cells in the exponential and stationary phase of growth has been studied. A transient accumulation of the amino acid occurred in the presence of an inwardly directed sodium gradient, in both conditions. However, the height and the shape of the overshoot curve differed noticeably in the two preparations. The accumulation ratio increased three-fold and the maximal uptake value occurred at an earlier time in plasma membrane vesicles from exponential growing rather than stationary phase cells. This might suggest that one of the two systems, A or ASC, serving hepatocytes, is fully expressed only in the exponential phase of growth or, alternatively, that the kinetic parameters of a possibly unique transport system are modified. Inhibition, countertransport as well as adaptive stimulation experiments and kinetic studies suggested the presence of a unique carrier-mediated transport of alanine in both phases of growth. The Vmax value was drastically reduced in the stationary phase of growth whereas the Km value was almost the same in both preparations. Therefore, the differences in time courses observed could be related to changes of the Vmax of a single transport agency rather than to the appearance/disappearance of an additional transport system (e.g. system A) in the conditions studied.