gamma-Aminobutyric acid transport in reconstituted preparations from rat brain: coupled sodium and chloride fluxes

Transport of gamma-aminobutyric acid (GABA) is electrogenic and completely depends on the presence of both sodium and chloride ions. These ions appear to be cotransported with gamma-aminobutyric acid through its transporter [reviewed in Kanner, B. I. (1983) Biochim. Biophys. Acta 726, 293-316]. Using proteoliposomes into which a partially purified gamma-aminobutyric acid transporter preparation was reconstituted, we have been able--for the first time--to provide direct evidence for sodium- and chloride-coupled gamma-aminobutyric acid transport. This has been done by measuring the fluxes of 22Na+, 36Cl-, and [3H]GABA. These fluxes have the following characteristics: There are components of the net fluxes of sodium and chloride that are gamma-aminobutyric acid dependent. The sodium flux is chloride dependent; i.e., when Cl- is replaced by inorganic phosphate or by SO4(2-), gamma-aminobutyric acid dependent sodium fluxes are abolished. The chloride flux is sodium dependent; i.e., when Na+ is replaced by Tris+ or by Li+, gamma-aminobutyric acid dependent chloride fluxes are abolished. Thus, the gamma-aminobutyric acid dependent sodium and chloride fluxes appear to be catalyzed by the transporter. Using these fluxes we have attempted to determine the stoichiometry of the process. We measured the initial rate of sodium-dependent gamma-aminobutyric acid fluxes and that of gamma-aminobutyric acid dependent sodium fluxes. This yields the stoichiometry between sodium and gamma-aminobutyric acid (2.58 +/- 0.99). Similarly, we measured the stoichiometry between chloride and gamma-aminobutyric acid, which is found to be 1.27 +/- 0.12.(ABSTRACT TRUNCATED AT 250 WORDS)