Characterization of gamma-aminobutyric acid binding sites on crude synaptic membranes.
[3H]GABA binding to crude synaptic membranes of rat brain was studied in an attempt to identify GABA binding to its synaptic receptor in the presence of Na+. Membrane vesicles prepared from crude synaptic membrane fractions were useful as a tool to differentiate synaptic GABA receptors from GABA uptake sites. The crude synaptic membranes treated with Triton X-100 [membranes (TX)] involved two classes of GABA binding sites (KD = 38.7 and 78.0 nM) in the absence of Na+, but the high-affinity sites disappeared in the presence of Na+ and a single class of GABA binding sites (KD = 75.0 nM) was detected. The failure to detect an active uptake of [3H]GABA into the vesicles prepared from membranes (TX) suggests that the [3H]GABA binding in the presence of Na+ was related to synaptic GABA receptors. It is probable that Na+ could mask the presence of the high-affinity class of GABA receptor.
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011963:Receptors, GABA-A; D012964:Sodium / Q000494:pharmacology; D013570:Synaptic Membranes / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D012964:Sodium