THE EFFECT OF ELECTRICAL STIMULATION AND HIGH POTASSIUM CONCENTRATIONS ON THE EFFLUX OF [3H] γ‐AMINOBUTYRIC ACID FROM BRAIN SLICES

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Abstract
Abstract— Brain slices were incubated with [3H]GABA in a medium containing aminooxyacetic acid to prevent metabolism of [3H]GABA by GABA‐glutamate transaminase. The slices, which rapidly accumulated radioactivity, were then continuously perfused and the efflux of [3H]GABA from the tissue was measured. The spontaneous efflux of [3H]GABA consisted of an initial rapid phase followed by a much slower release of [3[H]GABA. After 40 min perfusion 90 per cent of the radioactivity remained in the tissue.The slices were depolarized by electrical stimulation or by perfusion with a medium containing a high potassium concentration (40 mM). These procedures caused a striking increase in the efflux of [3H]GABA. The increased efflux produced by potassium, but not that produced by electrical stimulation, was dependent on calcium ions in the medium. The effect of electrical stimulation on [3H]GABA release was considerably reduced by a raised concentration (10 mM) of magnesium in the medium.High potassium concentrations and electrical stimulation did not cause an increase in the efflux of [14C]urea, L‐[3H]leucine or [14C]α‐amino‐isobutyric acid from brain slices. These results are consistent with the suggestion that GABA may be an inhibitory transmitter in the cerebral cortex.