Na-dependent L-glutamate transport bv eel intestinal J BBMV: role of K+ and Cl-

tamate uptake into eel (AnguiZla anguilla) intestinal brush-border membrane vesicles (BBMV) was a sigmoidal function of extravesicular Na, suggesting that two or more cations accompanied the amino acid during transport. L-[3H]glutamate influx illustrated the following kinetic constants: apparent membrane binding affinity (Kapp) = 0.80 t 0.12 mM; influx velocity (JmLt,) = 2.61 t 0.31 nmol mg protein-‘. min-‘; and permeability coefficient (P) = 0.65 t 0.10 ~1. mg protein-l. min. Results from the imposition of diffusion potentials across vesicle membranes using K-valinomycin or H-carbonyl-cyanide p-chloromethoxyphenylhydrazone suggested that Na-dependent L-glutamate transport was sensitive to transmem-brane electrical potential difference. Extravesicular aspartate was a competitive inhibitor of L- [3H]glutamate influx [inhibi-tory constant (Ki) = 0.28 t 0.04 mM]. Intravesicular K an