Characterization of barbiturate-stimulated chloride efflux from rat brain synaptoneurosomes

R. D. Schwartz, J. A. Jackson, D. Weigert, P. Skolnick, S. M. Paul

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Abstract

Membrane chloride (Cl-) permeability was studied in a novel subcellular brain preparation, the synaptoneurosome. Using a radioactive tracer exchange technique, Cl- transport was determined by measuring 36Cl- efflux from rat cerebral cortical synaptoneurosomes. Barbiturates increased 36Cl- efflux in a dose-dependent manner with the following relative order of potency: 5-(1,3-dimethylbutyl)-5-ethyl barbituric acid ((-)-DMBB) > pentobarbital > secobarbital > (+)-DMBB > hexobarbital > amobarbital > mephobarbital. Phenobarbital and barbital were virtually inactive. A good correlation was observed between the potencies of these barbiturates in stimulating 36Cl- efflux and their anesthetic potencies in mice (r = 0.90, p < 0.01) and their abilities to enhance [3H]diazepam binding to brain membranes (r = 0.77, p < 0.05). The effect of pentobarbital in enhancing 36Cl- efflux was reversed by the γ-aminobutyric acid (GABA) antagonists picrotoxin and bicuculline. Picrotoxin and bicuculline both decreased 36Cl- efflux in the absence of pentobarbital, suggesting the presence of endogenous GABA. Incubation of synaptoneurosomes with 4,4'-di-isothiocyano- or dinitro-2,2'-disulfonic acid stilbene, inhibitors of anion transport, also decreased both basal and pentobarbital-induced 36Cl- efflux. Pentobarbital (500 μM) was most effective in inducing 36Cl- efflux in the cerebellum, hippocampus, and cortex (23.7, 23.6, and 22.5%, respectively), and was less effective in stimulating 36Cl- efflux in the striatum (15.1%) and pons-medulla (6.2%). The relative efficacy of pentobarbital in enhancing 36Cl- efflux among these various brain regions was highly correlated (r = 0.96, p = 0.01) with the relative densities of [35S]-t-butylbicyclophosphorothionate-binding sites, a measure of GABA-gated Cl- channel density. These data suggest that pharmacologically relevant Cl- transport associated with the benzodiazepine/GABA/Cl- ionophore receptor complex can be measured in a subcellular preparation from brain, the synaptoneurosome.

Original languageEnglish
Pages (from-to)2963-2970
Number of pages8
JournalJournal of Neuroscience
Volume5
Issue number11
StatePublished - Dec 1 1985
Externally publishedYes

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    Schwartz, R. D., Jackson, J. A., Weigert, D., Skolnick, P., & Paul, S. M. (1985). Characterization of barbiturate-stimulated chloride efflux from rat brain synaptoneurosomes. Journal of Neuroscience, 5(11), 2963-2970.