Cell Surface Stability of γ-Aminobutyric Acid Type A Receptors

Abstract

Type A γ-aminobutyric acid receptors (GABAA), the major sites of fast synaptic inhibition in the brain, are believed to be composed predominantly of α, β, and γ subunits. Although cell surface expression is essential for GABAA receptor function, little is known regarding its regulation. To address this issue, the membrane stability of recombinant α1β2 or α1β2γ2 receptors was analyzed in human embryonic kidney cells. α1β2γ2 but not α1β2 receptors were found to recycle constitutively between the cell surface and a microtubule-dependent, perinuclear endosomal compartment. Similar GABAA receptor endocytosis was also seen in cultured hippocampal and cortical neurons. GABAA receptor surface levels were reduced upon protein kinase C (PKC) activation. Like basal endocytosis, this response required the γ2subunit but not receptor phosphorylation. Although inhibiting PKC activity did not block α1β2γ2receptor endocytosis, it did prevent receptor down-regulation, suggesting that PKC activity may block α1β2γ2 receptor recycling to the cell surface. In agreement with this observation, blocking recycling from endosomes with wortmannin selectively reduced surface levels of γ2-containing receptors. Together, our results demonstrate that the surface stability of GABAA receptors can be dynamically and specifically regulated, enabling neurons to modulate cell surface receptor number upon the appropriate cues.