Two pharmacologically distinct sodium- and chloride-coupled high-affinity gamma-aminobutyric acid transporters are present in plasma membrane vesicles and reconstituted preparations from rat brain.
Electrogenic sodium- and chloride-dependent gamma-aminobutyric acid (GABA) transport in crude synaptosomal membrane vesicles is partly inhibited by saturating levels of either of the substrate analogues cis-3-aminocyclohexanecarboxylic acid (ACHC) or beta-alanine. However, both of them together potently and fully inhibit the process. Transport of beta-alanine, which exhibits an apparent Km of about 44 microM, is also electrogenic and sodium and chloride dependent and competitively inhibited by GABA with a Ki of about 3 microM. This value is very similar to the Km of 2-4 microM found for GABA transport. On the other hand, ACHC does not inhibit beta-alanine transport at all. Upon solubilization of the membrane proteins with cholate and fractionation with ammonium sulfate, a fraction is obtained which upon reconstitution into proteoliposomes exhibits 4- to 10-fold-increased GABA transport. This activity is fully inhibited by low concentrations of ACHC and is not sensitive at all to beta-alanine. GABA transport in this preparation exhibits an apparent Km of about 2.5 microM and it is competitively inhibited by ACHC (Ki approximately 7 microM). These data indicate the presence of two GABA transporter subtypes in the membrane vesicles: the A type, sensitive to ACHC, and the B type, sensitive to beta-alanine.
Kanner
B I
BI
Department of Biochemistry, Hadassah Medical School, Hebrew University, Jerusalem, Israel.
Bendahan
A
A
D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology*; D050485:GABA Plasma Membrane Transport Proteins; D007700:Kinetics; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000302:isolation & purification / Q000378:metabolism*; D027361:Organic Anion Transporters; D051381:Rats; D012964:Sodium / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism; D015091:beta-Alanine / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002352:Carrier Proteins; D002712:Chlorides; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D027361:Organic Anion Transporters; D015091:beta-Alanine; D005680:gamma-Aminobutyric Acid; D012964:Sodium