Molecular Pharmacology, Vol 20, 287-294, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

Ethanol Enhances [³H]Diazepam Binding at the Benzodiazepine--Aminobutyric Acid Receptor-Ionophore Complex

¹ Division of Molecular Pharmacology, Department of Pharmacology, The University of Texas Health Science Center, San Antonio, Texas 78284

Ethanol, which has a pharmacological profile similar to those of barbiturates and benzodiazepines, enhances [³H]diazepam binding to the crude Lubrol-solubilized fraction. This fraction had specific binding sites for [³H]diazepam, [³H]muscimol, and [-³H]dihydropicrotoxinin (DHP). Ethanol enhanced [³H]diazepam to this fraction in a dose-dependent manner with a maximal enhancement of 90 ± 8.5% occurring at 100 mM and a half-maximal effect occurring at 30 mM. Ethanol (100 mM) changed the K_D from a control value of 9.36 ± 126 to 4.40 ± 0.33 nM (p > 0.005). The B_max of [³H]diazepam binding was not significantly altered. The enhancing effect of ethanol was blocked by picrotoxinin and (+)-bicuculline. Ethanol, while enhancing [³H]diazepam binding to the crude Lubrol fraction, inhibited partially the binding of [³H]DHP and had no effect on [³H]muscimol binding. The rank order of enhancement of [³H]diazepam binding with various alcohols (ethanol > methanol > isopropyl alcohol > propanol-1 = t-butyl alcohol = butanol-1) did not agree with their partition coefficients. These results suggest that ethanol, like pentobarbital, enhances [³H]diazepam binding at the benzodiazepine--aminobutyric acid (GABA) receptor-ionophore complex. This interaction will result in facilitation of GABAergic transmission and may be responsible for some of the central effects of alcohol, such as antianxiety, muscle relaxant, and sedative. We also provide evidence that ethanol does not enhance [³H]diazepam directly at the benzodiazepine binding site, but, rather, indirectly via the picrotoxinin-sensitive site of the benzodiazepine-GABA receptor-ionophore complex.

Note:
ACKNOWLEDGMENTS We thank Dr. M. Javors for helpful comments, I. Chen and T. Burch for excellent technical assistance, and J. Priddy for secretarial help. We also thank Dr. G. Mott for measuring the cholesterol content in the crude Lubrol-solubilized fraction.

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