The binding of [3H]muscimol, a gamma-aminobutyrate (GABA) receptor agonist, to a membrane preparation from pig cerebral cortex was enhanced by the anaesthetic propanidid in a concentration-dependent manner. At 0 degrees C, binding was stimulated to 220% of control values, with 50% stimulation at 60 microM-propanidid. At 37 degrees C, propanidid caused a more powerful stimulation of [3H]muscimol binding (340% of control values). Propanidid (1 mM) exerted little effect on the affinity of muscimol binding (KD approx. 10 nM), but increased the apparent number of high-affinity binding sites in the membrane by 2-fold. Enhancement of [3H]muscimol binding was observed only in the presence of Cl- ions, half-maximal activation being achieved at approx. 40 mM-Cl-. Picrotoxinin inhibited the stimulation of [3H]muscimol binding by propanidid with an IC50 (concentration causing 50% inhibition) value of approx. 25 microM. The enhancement of [3H]muscimol binding by propanidid was not additive with the enhancement produced by secobarbital. Phenobarbital inhibited the effect of propanidid and secobarbital. The GABA receptor was solubilized with Triton X-100 or with Chaps [3-[(3-cholamidopropyl)dimethylammonio]propanesulphonate]. Propanidid and secobarbital did not stimulate the binding of [3H]muscimol after solubilization with Triton X-100. However, the receptor could be solubilized by 5 mM-Chaps with retention of the stimulatory effects of propanidid and secobarbital. Unlike barbiturates, propanidid did not stimulate the binding of [3H]flunitrazepam to membranes. It is suggested that the ability to modulate the [3H]muscimol site of the GABA-receptor complex may be a common and perhaps functional characteristic of general anaesthetics.
The γ-aminobutyrate/benzodiazepine receptor from pig brain. Enhancement of γ-aminobutyrate-receptor binding by the anaesthetic propanidid
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E F Kirkness, A J Turner; The γ-aminobutyrate/benzodiazepine receptor from pig brain. Enhancement of γ-aminobutyrate-receptor binding by the anaesthetic propanidid. Biochem J 1 January 1986; 233 (1): 259–264. doi: https://doi.org/10.1042/bj2330259
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