Stimulation of adenylyl cyclase mediated by phospholipase C-linked M3 muscarinic receptor in human neuroblastoma SK-N-BE (2) C cells.

Muscarinic receptor in human neuroblastoma SK-N-BE(2)C cells was identified and characterized. Treatment of the cells with carbachol evoked the generation of inositol 1,4,5-trisphosphate (IP3) with a peak level reached at 1 min after stimulation. Carbachol increased intracellular Ca2+ ([Ca2+]i) with an EC50 value of 35 microM. In addition, carbachol produced a 1.3-3-fold increase in the cyclic AMP (cAMP) level compared with untreated control and elevated synergistically the cAMP level in the treatment with prostaglandin E2 (PGE2). The M3 antagonist p-fluorohexahydrosiladifenidol (IC50 = 0.5-0.8 microM) inhibited the increases in [Ca2+]i, IP3, and cAMP more effectively than the M1 antagonist pirenzepine (IC50 = 5-9 microM) and the M2 antagonist methoctramine (IC50 = 20-30 microM). The involvements of [Ca2+]i elevation and protein kinase C activation induced by phospholipase C activation were tested in the carbachol-induced cAMP production. The calcium chelator BAPTA/AM (75 microM) inhibited significantly the synergistic effects of carbachol and PGE2 on the production of cAMP, whereas the Ca2+ ionophore ionomycin (1 microM) clearly enhanced PGE2-induced cAMP production. However, phorbol 12-myristate 13-acetate did not enhance PGE2-stimulated cAMP production. These data suggest that phospholipase C-linked M3 receptors are present and that stimulation of the receptors activates adenylyl cyclase, at least in part, by the Ca(2+)-dependent system in the neuronal cells.