In the present study plasma membrane vesicles were prepared from livers of control and alloxan-induced diabetic rats and the substrate specificity and kinetic characteristics of alanine transport determined in both groups. Sodium-dependent alanine uptake at physiological alanine concentrations (100 microM) was enhanced threefold in diabetic as compared with control animals (0.31 +/- 0.04 vs. 0.11 +/- 0.01 nmol X mg protein-1 X 10 s-1). This accelerated influx corresponded to a three- to fourfold increase in the Vmax of alanine transport in diabetic versus control group (7.1 +/- 2.1 vs. 1.6 +/- 0.2 nmol X mg protein-1 X 10 s-1, P less than 0.05), whereas the Km of alanine uptake was unchanged (2.8 +/- 1.2 vs. 1.4 +/- 0.1 mM). Other neutral amino acids (20 mM) inhibited alanine transport to a similar degree in both groups. The sodium-dependent influx of glutamine (100 microM) was similar in diabetic and control groups (0.17 +/- 0.03 and 0.14 +/- 0.02 nmol X mg protein-1 X 10 s-1, respectively). The initial velocity of 22Na uptake (80 mM) into vesicles and half-maximal stimulation of alanine transport was achieved at essentially identical sodium concentrations (approximately 40 mM) in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)