L-alanine transport in small intestine brush-border membrane vesicles of obese rats.

Membrane vesicles from the small intestine brush border were obtained and used to determine the possible effects of genetic or nutritional obesity on L-alanine uptake. Membrane vesicles from Zucker fa/fa obese rats and cafeteria diet-fed Zucker Fa/? rats showed the same characteristics as those of standard diet-fed lean animals. All preparations showed sodium-dependent transport as the main pathway for L-alanine uptake within the substrate concentration range tested. The apparent substrate affinity constant (Km) values and the pattern of inhibition of Na(+)-dependent L-alanine uptake by other amino acids (L-leucine and L-glutamine), suggests that system B involved in the transport of dipolar amino acids (formerly named Neutral Brush Border System) participates in the Na(+)-dependent transport of L-alanine. The affinity constant (Km) for L-alanine was essentially the same for all the groups studied (in the range of 10 mM). However, there was a higher (P < 0.05) maximal capacity (Vmax) in preparations from diet-induced obese animals (cafeteria diet) than that of genetically obese rats. These results indicate that either nutritional or genetic obesity may modify the capacity but not the affinity of transport systems for L-alanine uptake in the brush border of rat small intestine.