ETHANOL INHIBITS THE PEAK OF MUSCARINIC RECEPTOR-STIMULATED FORMATIONOF INOSITOL 1,4,5-TRISPHOSPHATE IN NEUROBLASTOMA SH-SY5Y CELLS

The effect of ethanol on muscarinic receptor-stimulated formation of i nositol 1,4,5-trisphosphate was studied in human neuroblastoma SH-SY5Y cells. Stimulation with carbachol induced a biphasic increase of inos itol 1,4,5-trisphosphate with an initial peak after 10 sec declining t o a plateau phase of elevation above basal levels, which was sustained for at least 5 min in the presence of agonist. The peak, but not the plateau phase, was concentration-dependently decreased by exposure to ethanol. Maximal inhibition was obtained within 30 sec of exposure to ethanol. Ethanol caused an increase in the EC(50) value of carbachol f or the initial rate of inositol 1,4,5-trisphosphate formation, measure d after 10 sec of stimulation, from 98 mu M in the absence to 196 mu M in the presence of 100 mM ethanol. The potencies of pirenzepine and h exahydro-sila-difenidol hydrochloride for inhibiting [H-3]quinuclidiny l benzilate binding and inositol 1,4,5-trisphophate formation suggest that both phases are mediated via the muscarinic M(1) receptor. Phorbo l 12-myristate 13-acetate inhibited both phases of inositol 1,4,5-tris phosphate formation, whereas okadaic acid and modulators of cAMP-depen dent protein kinase were without any effect. There was no inhibitory e ffect of ethanol when protein kinase C was inhibited by H7 and calphos tin C, indicating that the ethanol effect is dependent on protein kina se C activity.