ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: The binding of [3H] γ-aminobutyric acid ([3H]GABA) and [3H]muscimol has been studied in purified synaptic plasma membrane (SPM) preparations from rat brain. Scatchard analysis of specific binding (defined as that displaced by 100 μMγ-aminobutyrate) indicated that the binding of both radiolabelled ligands was best described by a two component Langmuir adsorption isotherm. The apparent KD and Bmax values for [3H]GABA at 4°C were KD1, 20 nM; KD2,165 nM; Bmax1, 0.48 pmol;Bmax2, 6.0 pmol. mg−1; for [3H]muscimol at 4°C they were: KD1, 1.75 nM; KD2, 17.5 nM; Bmaxl, 0.84 pmol. mg−1; Bmax2, 4.8 pmol.mg−1; and for [3H]muscimol at 37°C they were: KD1, 7.0 nM; Km, 60 nM; Bmax], 0.5 pmol-mg−1; Bmax2, 7.2 pmol-mg1. Under the experimental conditions used, the similar Bmilx values for [3H]GABA and [3H]muscimol binding to the SPM preparations suggests that the high- and low-affinity components for the two radiolabeled ligands are identical. The effects of the GAB A antagonist bicuculline on the binding of [3H]muscimol at 4CC and 37°C were studied. At 4°C, antagonism of muscimol binding appeared to be competitive at the high-affinity site but noncompetitive at the low-affinity site. At 37°C, antagonism was again competitive at the high-affinity site but was of a mixed competitive/noncompetitive nature at the low-affinity site. Assuming that binding to the high-affinity site is associated with the pharmacological actions of bicuculline, the apparent KD values obtained suggest a pA2 value of 5.3 against [3H]muscimol at 4°C and 37°C. This figure is in good agreement with several estimates of the potency of bicuculline based on pharmacological measurements. Results from displacement studies using [3H]GABA and [3H]muscimol suggest that [3H]GABA might be a more satisfactory ligand than [3H]muscimol in GABA radioreceptor assays.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1982.tb04700.x
