Na-dependent L-glutamate transport by eel intestinal BBMV: role of K+ and Cl-.
L-[3H]glutamate uptake into eel (Anguilla 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 +/- 0.12 mM; influx velocity (Jmax) = 2.61 +/- 0.31 nmol.mg protein-1.min-1; and permeability coefficient (P) = 0.65 +/- 0.10 microliters.mg protein-1. min-1. 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 transmembrane electrical potential difference. Extravesicular aspartate was a competitive inhibitor of L-[3H]glutamate influx [inhibitory constant (Ki) = 0.28 +/- 0.04 mM]. Intravesicular K and extravesicular Cl ions enhanced maximal amino acid influx and transient L-glutamate accumulation against a concentration gradient (overshoot). Intravesicular K reduced the Kapp of the membrane to L-glutamate, whereas extravesicular Cl increased L-glutamate Jmax. A model for L-[3H]glutamate transport is suggested involving the cotransport of at least two Na and one L-glutamate that is activated by one intravesicular K ion and at least two extravesicular Cl ions.
Romano
P M
PM
Dipartimento di Biologia, Università di Lecce, Italy.
Ahearn
G A
GA
Storelli
C
C
D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001692:Biological Transport; D002712:Chlorides / Q000502:physiology*; D004524:Eels / Q000378:metabolism; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000648:ultrastructure; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011188:Potassium / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology*
D002712:Chlorides; D005971:Glutamates; D001224:Aspartic Acid; D018698:Glutamic Acid; D012964:Sodium; D011188:Potassium