Components of basal and GABA activated 36Cl- influx in rat cerebral cortex microsacs

The basal and GABA activated accumulation of labelled chloride in rat cerebral cortex microsacs has been studied as a function of incubation time. Basal accumulation has biphasic kinetics within 2 minutes of incubation with two components clearly visible. GABA activated stimulation has two phases as well, starting from (GABA) = 10(-5) M, one appearing within seconds of incubation range and the other one within tens of seconds. Both GABA-activated components are blocked by bicuculline methiodide (BMI). Practically no effect by 10(-3) M nipecotic acid was found on either the comparatively rapid or the slower phase. The two GABA activated components may correspond to two different populations of sealed vesicles with different receptor concentration per internal volume.