Inhibition of the GABA receptor-gated chloride ion channel in brain by noncompetitive inhibitors of the nicotinic receptor-gated cation channel.

Published

Journal Article

The ability of various noncompetitive inhibitors (NCI) of the nicotinic acetylcholine receptor to inhibit gamma-aminobutyric acidA (GABA) receptor activity in brain was investigated. Micromolar concentrations of NCI such as tetraphenylphosphonium, mepacrine, chlorpromazine and phencyclidine inhibited muscimol-induced 36chloride (36Cl-) uptake in rat cerebral cortical synaptoneurosomes in a noncompetitive manner. D-Tubocurarine behaved as a competitive inhibitor. In experiments measuring the time course of muscimol-induced 36Cl- uptake, a decline in the apparent transport rate constant (k') (reflection of desensitization) occurred over the first 3 sec. At lowered temperature (22 degrees C) the k' did not decline during the first 4 sec. Under these conditions preincubation of the vesicles with tetraphenylphosphonium caused a marked decline in the apparent k' over the first 5 sec (transition T1/2 of 1.04 sec) suggesting that tetraphenylphosphonium promotes desensitization of the GABA receptor. The inhibition of muscimol-induced 36Cl- uptake by NCI was reduced in the absence of Ca++. In addition, Ca++ decreased the potency of muscimol to stimulate 36Cl- uptake with an IC50 = 64 microM. The interaction of NCI with GABA agonist and convulsant sites associated with the GABA receptor-gated Cl- channel also was investigated. NCI antagonized noncompetitively [3H]t-butylbicycloorthobenzoate binding to convulsant sites whereas only mepacrine and chlorpromazine antagonized binding of [3H]muscimol to agonist sites. These findings suggest that 1) inhibition of the GABA receptor-gated Cl- channel by NCI may explain the convulsant properties of several of these compounds and 2) there may be structural domains common to the GABA receptor and nicotinic receptor-gated ion channels that selectively permit interactions with various NCI.

Full Text

Duke Authors

Cited Authors

  • Schwartz, RD; Mindlin, MC

Published Date

  • March 1988

Published In

Volume / Issue

  • 244 / 3

Start / End Page

  • 963 - 970

PubMed ID

  • 2472481

Pubmed Central ID

  • 2472481

International Standard Serial Number (ISSN)

  • 0022-3565

Language

  • eng

Conference Location

  • United States