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Substrate Specificity of [ 3 H] Muscimol Binding to a Particulate Fraction of a Neuron‐enriched Culture of Embryonic Rat Brain
Author(s) -
DeFeudis Francis V.,
Ossola Lucienne,
Schmitt Gaby,
Mandel Paul
Publication year - 1980
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1980.tb09656.x
Subject(s) - muscimol , nipecotic acid , chemistry , bicuculline , biochemistry , strychnine , receptor , biophysics , gaba receptor antagonist , binding site , gabaa receptor , biology , neurotransmitter
The effects of some GABA analogues and some drugs on the binding of [ 3 H]muscimol (3.08 nM) to thoroughly washed subcellular particles prepared from a neuron‐enriched culture of embryonic rat brain were examined using Na+‐free Tris‐citrate medium and a centrifugation method. Competition for [ 3 H]muscimol binding sites by excess(10 −5 M) unlabelled GABA provided estimates of “specific” binding. In accord with in vivo neuropharmacological studies on GABA receptors and with in vitro studies on cerebral membrane preparations, [ 3 H]muscimol binding was potently inhibited by muscimol itself (IC 50 , 2.5 nM), GABA (1C 50 , 43 nM), isoguvacine (IC 50 , 61 nM), and 3‐aminopropanesulphonic acid (IC 50 , 160 nM), and less potently inhibited by the GABA antagonist bicuculline methobromide (IC 50 , 800 nM). δ‐ Aminovaleric acid (IC 50 , 2.6 μM), the glycinelp‐alanine antagonist strychnine (IC 50 , 6.6 μM), and the predominantly glial GABA uptake inhibitors β‐alanine (IC 50 , 23 μM) and p‐proline (IC 50 , 66 μM) also inhibited [ 3 H]muscimol binding. Other inhibitors of Na+‐dependent GABA uptake, (±)‐nipecotic acid, L‐ 2,4‐diaminobutyric acid, and guvacine, as well as picrotoxinin, were relatively inactive as inhibitors of [ 3 H]muscimol binding (IC 50 ≥ 1 mM). In addition to revealing that GABA receptors are present on neuronal membranes before the formation of most synapses, this binding of [ 3 H]muscimol that occurs to neuronal, but not to glial, membranes might be useful as a “neuronal marker” and for the further characterization and isolation of GABA receptors.