Cell surface stability of gamma-aminobutyric acid type A receptors - Dependence on protein kinase C activity and subunit composition

Type A gamma-aminobutyric acid receptors (GABA(A)), the major sites of fast synaptic inhibition in the brain, are believed to be composed predominantl y of alpha, beta, and gamma subunits, Although cell surface expression is e ssential for GABA,receptor function, little is known regarding its regulati on, To address this issue, the membrane stability of recombinant alpha(1)be ta(2) or alpha(1)beta(2)gamma(2) receptors was analyzed in human embryonic kidney cells. alpha(1)beta(2)gamma(2), but not alpha(1)beta(2) receptors we re found to recycle constitutively between the cell surface and a microtubu le-dependent, perinuclear endosomal compartment. Similar GABA, receptor end ocytosis was also seen in cultured hippocampal and cortical neurons. GABA, receptor surface levels were reduced upon protein kinase C (PKC) activation . Like basal endocytosis, this response required the gamma(2) subunit but n ot receptor phosphorylation. Although inhibiting PKC activity did not block alpha(1)beta(2)gamma(2) receptor endocytosis, it did prevent receptor down -regulation, suggesting that PKC activity may block alpha(1)beta(2)gamma(2) receptor recycling to the cell surface, In agreement with this observation , blocking recycling from endosomes with wortmannin selectively reduced sur face levels of gamma(2)-containing receptors, Together, our results demonst rate that the surface stability of GABA(A) receptors can be dynamically and specifically regulated, enabling neurons to modulate cell surface receptor number upon the appropriate cues.