GABAA receptors of cerebellar granule cells in culture: explanation of overall insensitivity to ethanol

GABA-activated chloride currents were studied in cerebellar granule cells put in culture from neonatal rats. As previously described, 10 μM GABA perfusion of these cells recorded by whole cell patch-clamp elicits chloride currents displaying a peak and a steady-state component. The two components were studied in the presence of 1 mM furosemide, 1 μM Zn2+ and a combination of the two in order to evaluate the contribution of the different types of GABAA receptors. Furosemide inhibits α6 containing receptors whereas low levels of Zn2+ specifically block incomplete GABAA receptors made up of α and β subunits only. The results show that the peak component involves the following receptors: αx βy, 25%; α1 βy γ2, 45%; α6 βy γ2 plus α1 α6 βy γ2, 30%. The steady state component is made up by αx βy, 38%; α1 βy δ, 62%. Ethanol at relatively high concentration, 100 mM, slows further down the desensitization of α1 βy δ receptors. The results indicate that the relative insensitivity to ethanol of GABAA receptors of neonatal cerebellar granule cells in culture is due to the absence of mature α6 βy δ receptors, a major receptor brand involved in tonic inhibition.