Regulation of GABA receptor binding to synaptic plasma membrane of rat cerebral cortex: the role of endogenous phospholipids.
Triton X-100 treatments produced an extensive depletion of proteins and phospholipids and a marked increase of [3H] GABA binding on synaptic plasma membranes (SPM). Maximal [3H]GABA binding was obtained with three Triton X-100 treatments (+ 174% with respect to control). Phospholipase C, which removes only the phospholipid polar head, induces a 40% increase of [3H]GABA binding only after treatments resulting in extensive protein depletion. In reconstitution experiments phosphatidylethanolamine, the largest phospholipid removed, induced a 30-35% inhibition of [3H]GABA binding in Triton X-100 treated membranes; in contrast phosphatidylserine and phosphatidylcholine did not produce significant changes. The reconstitution of phospholipase C-treated SPM preparations with exogenous phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine or phosphoethanolamine and 1,2-dipalmitoylglycerol, products of phospholipase C activity, did not yield significant changes. This evidence, which argues against a direct role of phospholipids on the regulation of GABA binding, should, however, suggest that the GABA binding component of the receptor site is a lipoprotein or a lipid-depending protein.