Co-assembly of GABA ρ subunits with the GABA A receptor γ 2 subunit cloned from white perch retina

Abstract

Although it is well established that GABA C receptors are comprised in part of GABA ρ subunits, the exact subunit composition of neuronal GABA C receptors is yet to be determined. A detailed comparison of GABA C-mediated neuronal responses elicited from retinal neurons with those obtained from receptors formed by GABA ρ subunits revealed a number of significant differences both in the kinetics and the pharmacology of the responses. Our previous studies indicated that the human GABA A receptor γ 2 subunit could co-assemble with one (ρ 1B) of the white perch GABA ρ subunits to form a heterooligomeric receptor with properties that resembled those of the GABA C receptors on white perch bipolar cells. In this study, we cloned the white perch γ 2 subunit, and investigated its co-assembly with four white perch GABA ρ subunits. When expressed in Xenopus oocytes, perch γ 2 and ρ 1B subunits form heterooligomeric receptors with distinct properties: the GABA-elicited responses have fast kinetics and are sensitive to pentobarbital modulation. The enhancement of GABA-elicited responses by pentobarbital on the heterooligomeric receptors could be eliminated by a single mutation in the third transmembrane domain of the γ 2 subunit, indicating that pentobarbital sensitivity is mediated by the incorporated γ 2 subunit. On the other hand, co-expression of the perch γ 2 subunit with the other perch GABA ρ subunits produced no detectable changes in the kinetics of GABA-elicited response or the sensitivity to pentobarbital modulation. These results suggest that the γ 2 subunit can co-assemble only with one (ρ 1B), but not with other white perch GABA ρ subunits.