ETHANOL DISRUPTS CARBAMYLCHOLINE-STIMULATED RELEASE OF ARACHIDONIC-ACID FROM CHINESE-HAMSTER OVARY CELLS EXPRESSING DIFFERENT SUBTYPES OF HUMAN MUSCARINIC RECEPTOR

Ethanol disrupts signal transduction mediated by a variety of G-protei n coupled receptors, We examined the effects of ethanol on arachidonic acid release mediated by muscarinic acetylcholine receptors, Chinese hamster ovary (CHO) cells transfected with the different subtypes of h uman muscarinic receptors (M1 to M5) were incubated with [H-3]arachido nic acid ([H-3]AA) for 18 hr, washed, and exposed to the cholinergic a gonist carbamylcholine for 15 min. Carbamylcholine induced [H-3]AA rel ease from CHO cells expressing M1, M3, or M5, but not M2 or M4, muscar inic receptors, Dose response curves revealed that carbamylcholine sti mulated [H-3]AA release by up to 12-fold with an EC50 of approximate t o 0.4 mu M; maximal responses were obtained with 10 mu M carbamylcholi ne, Exposure of M1-, M3-, or M5- expressing cells to ethanol for 5 min before stimulating with carbamylcholine reduced [H-3]AA release by 40 to 65%; 50% of the maximal inhibition was obtained with an ethanol co ncentration of 30 to 50 mM, Ethanol did not affect basal [H-3]AA relea se measured in the absence of carbamylcholine, Dose response curves su ggest that ethanol acts as a noncompetitive inhibitor of muscarinic re ceptor-induced [H-3]AA release insofar as maximal [H-3]AA release was depressed in the presence of ethanol with no apparent change in the EC 50 for stimulation by carbamylcholine, Exposure of CHO cells to 38 mM ethanol for 48 hr increased [H-3]AA release induced by carbamylcholine without affecting basal [H-3]AA release or altering the EC50 for carb amylcholine, These results indicate that ethanol acutely inhibits musc arinic receptor signaling through the arachidonic acid pathway in a no ncompetitive manner, but chronically enhances muscarinic signaling thr ough the same pathway.