Ethanol blocks cytosolic Ca²⁺ responses triggered by activation of GABA_A receptor/Cl^- channels in cultured proliferating rat neuroepithelial cells

GABA_A receptor/Cl^- channels and voltage-gated Ca²⁺ channels are believed to be important sites of ethanol action in the CNS. Acute exposure of ethanol potentiates GABA_A receptor/Cl^- channel activity and inhibits voltage-gated Ca²⁺ channels in a number of preparations, mostly post-mitotic neurons. The effects of ethanol on these channels in primary cultures of undifferentiated neural precursor cells remain unknown. To address this issue, we examined the effects of ethanol on GABA_A agonist-activated elevation of cytosolic Ca²⁺ in an in vitro model of the cortical neuroepithelium derived from rat basic fibroblast growth factor-expanded neural precursor cells. We found a potent inhibition of GABA_A-activated elevation of cytosolic Ca²⁺ by ethanol in actively proliferating cells. Since we had recently demonstrated that GABA_A receptor activation depolarizes these cells and elevates their cytosolic Ca²⁺, we tested whether the effects of ethanol involved both GABA_A receptors and voltage-gated Ca²⁺ channels. Both extracellular K⁺- and muscimol-induced cytosolic Ca²⁺ elevations were abolished by nitrendipine, indicating that both depolarizing stimuli triggered Ca²⁺ influx through L-type voltage-gated Ca²⁺ channels. Exposure of proliferating cells to different concentrations of ethanol revealed that the drug was more potent in blocking muscimol-induced compared to K⁺-evoked cytosolic Ca²⁺ elevations. These results raise the possibility that ethanol blocks GABAergic stimulation of cytosolic Ca²⁺ levels in proliferating precursors primarily by interacting with GABA_A receptor/Cl^- channels and secondarily with voltage-gated Ca²⁺ channels.