title: Beta-alanine transport in synaptic plasma membrane vesicles from rat brain. Efflux, exchange and stoichiometry.
abstract: The efflux and exchange of beta-alanine were studied in synaptic plasma membrane vesicles from rat brain. The mechanism of beta-alanine translocation has been probed by comparing the ion dependence of net efflux to that of exchange. Dilution-induced efflux requires the simultaneous presence of internal sodium and chloride ions while influx is dependent on the presence of these two ions on the outside [Zafra, F., Aragón, M. C., Valdivieso, F. and Giménez, C. (1984) Neurochem Res. 9, 695-707]. These data show that the release of beta-alanine occurs via the carrier system and that it is cotransported with sodium and chloride ions. beta-Alanine efflux from the membrane vesicles is stimulated by external beta-alanine. This exchange does not require external sodium and chloride but it is dependent on the external concentration of beta-alanine. Half-maximal stimulation is obtained at a beta-alanine concentration similar to the Km for beta-alanine influx. Results of the direct measurements of the coupling of sodium and chloride to the transport of beta-alanine by using a kinetic approach allow us to propose a stoichiometry for the translocation cycle catalyzed by the beta-alanine transporter of three sodium ions and one chloride ion per beta-alanine zwitterion. To account for all the observed effects of external ions, beta-alanine concentrations and membrane potential on beta-alanine influx and efflux, a kinetic model of the Na+/Cl-/beta-alanine cotransport system is discussed.
mesh_terms: D000409:Alanine / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D003198:Computer Simulation; D066298:In Vitro Techniques; D008297:Male; D008954:Models, Biological; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism*; D015091:beta-Alanine / Q000378:metabolism*
chemical_list: D002712:Chlorides; D015091:beta-Alanine; D012964:Sodium; D000409:Alanine