GABA is the major inhibitory neurotransmitter in the CNS. It has been suggested that ethanol exerts its inhibitory effects on the CNS by potentiating the activity of the GABA-A receptor-gated chloride channel. However, electrophysiological and isotopic studies have provided conflicting evidence regarding the effects of ethanol on GABA-A activity. In an attempt to clarify this controversy and to gain further insight into the effects of ethanol on the function and regulation of the GABA-A channel, we have measured chloride flux in primary cultures of rat cerebellar neurons using the intracellular fluorescent probe, SPQ. Single cells were studied using a microscope - computer - photomultiplier system in order to characterize GABA-A responses within the population of viable cells. Chloride efflux from the cell down an imposed concentration gradient was observed over time. GABA dose dependently increased the rate of chloride efflux. The GABA response was sensitive to the GABA-A antagonist, bicuculline. Preliminary studies involving alcohol suggest that exposing the cells to GABA in the presence of physiologically relevant concentrations of ethanol further increase chloride efflux. Recent reports have suggested that cAMP-dependent phosphorylation inhibits GABA-A activity. Whether the mechanism of ethanol on the GABA channel is through cAMP-dependent pathways is currently under investigation.
