CHANGES IN ALANINE TRANSPORT IN PLASMA-MEMBRANE VESICLES FROM RAT-LIVER DURING THE EARLY STAGES OF DIETHYLNITROSAMINE-INDUCED HEPATOCARCINOGENESIS

The transport of L-alanihe, a natural substrate of system A, across liver plasma membrane vesicle preparations was modified during the early stages of rat DENA hepatocarcinogenesis. Kinetic studies indicated an increase of the V(max), with normal K(m) values, at 30 h in rats undergoing a partial hepatectomy. Normal V(max) and drastically reduced K(m) values were present using membrane preparations from liver tissue showing enzyme-altered hyperplastic foci and/or preneoplastic nodules. The results suggest that alanine transport is differently affected by initiating and promoting stimuli during rat DENA hepatocarcinogenesis. The changes of the V(max) could be related to the promoting effect of partial hepatectomy on cell proliferation whereas the changes of the affinity constant (K(m)) could be the result of intrinsic modifications of the transporter in initiated cells.