Regulation of amino acid and glucose transport activity expressed in isolated membranes from untransformed and SV 40-transformed mouse fibroblasts.

Membrane vesicles isolated from untransformed Balb/c and Swiss mouse fibroblasts and their SV 40-transformed derivatives were shown to catalyze carrier-mediated, intravesicular uptake of alpha-aminoisobutyric acid and D-glucose. Concentrative uptake of alpha-aminoisobutyric acid required the presence of a Na+-gradient (external greater than internal) and could occur independently of endogenous (Na+ + K+)ATPase activity. A K+ diffusion gradient (internal greater than external) in the presence of valinomycin, or the addition of the Na+ salt of a highly permeant anion, conditions expected to create an interior-negative membrane potential stimulated Na+-gradient-dependent uptake, suggesting this process is electrogenic. D-Glucose uptake was nonconcentrative and did not require ion gradients or metabolic conversion. Na+ gradient-dependent transport of alpha-aminoisobutyric acid was reduced both in initial rate and extent of uptake in vesicles from confluent untransformed cells and increased in those from SV 40-transformed cells, compared with activities observed in vesicles from proliferating untransformed cells. No changes in D-glucose carrier activity were observed when assayed at low glucose concentrations.