IDENTIFICATION OF THE M(3) MUSCARINIC RECEPTOR WHICH IS COUPLED TO PHOSPHOLIPASE-C AND ADENYLYL-CYCLASE IN SK-N-BE(2)C CELLS

The muscarinic cholinergic receptor in human neuroblastoma SK-N-BE(2)C cells was identified and characterized by treatment with carbachol, the cholinergic receptor agonist Carbachol (1 mM) increased the intracellular Ca2+ concentration ([Ca2+](i)) and the inositol 1,4,5-trisphosphate level, The muscarinic receptor antagonists decreased the above carbachol-induced responses with a potency order of p-fluorohexahydrosiladifenidol (IC50 = 0.5-0.8 mu M) > pirenzepine (IC50 = 5-9 mu M) > methoctramine (IC50 = 20-30 mu M), which are selective to M(3), M(1), and M(2) receptors, respectively, Carbachol slightly elevated the cAMP level by similar to 1.5 times but enhanced the prostaglandin E(2)-induced cAMP accumulation synergistically, which was then completely inhibited by the addition of 10 mu M atropine, the muscarinic receptor inhibitor. Carbachol-induced enhancement of cAMP accumulation was also inhibited by the specific antagonists with a potency order of M(3) > M(1) > M(2) and the IC50 values were similar to the values of inhibition of [Ca2+](i) rise and IP3 generation. Phorbol 12-myristate 13-acetate pretreatment decreased both carbachol-induced [Ca2+](i) rise and cAMP accumulation, These results indicate that the activation of phospholipase C and adenylyl cyclase mediated by M(3) muscarinic receptors is inhibited by protein kinase C stimulation.