Differentiation of NG108-15 cells induced by the combined presence of dbcAMP and dexamethasone brings about the expression of N and P/Q types of calcium channels and the inhibitory influence of muscarinic receptors on calcium influx

Differentiation of cholinergic cell line NG108-15 induced by a combination of dibutyryl cyclic AMP (dbcAMP) and dexamethasone enhances the cholinergic phenotype of the cells more than that induced by either agent alone. We in vestigated the effect of treatment with dbcAMP and dexamethasone on potassi um depolarization-evoked influx of calcium and its regulation by the muscar inic agonist carbachol. Depolarization of control cells and of cells differ entiated in the presence of dbcAMP or dexamethasone alone, or in the combin ed presence of dbcAMP and dexamethasone induced, respectively, 2.2-, 4.3-, 2.7- and 10.7-fold increases of the resting [Ca2+](i). Dexamethasone alone and the combination of dbcAMP and dexamethasone augmented the number of mus carinic receptors by 25 and 40%, respectively. Inhibitors of N (omega -cono toxin GVIA) or P/Q (omega -agatoxin TK) calcium channels had no effect on C a2+ influx in control cells, whereas in cells differentiated in the combine d presence of dbcAMP and dexamethasone they significantly diminished the in flux of Ca2+ by 20 and 5%, respectively. Carbachol attenuated calcium influ x in differentiated cells in an atropine-insensitive manner if it was prese nt during stimulation. This effect of carbachol was probably due to an open -channel block of L type channels. In the presence of nifedipine, carbachol attenuated the influx of Ca2+ into cells differentiated with dbcAMP and de xamethasone by 20% in an atropine-sensitive way. Data show that differentia tion of NG108-15 cells by dbcAMP and dexamethasone promotes the expression of functional nifedipine-insensitive N and P/Q types of Ca2+ channels and t hat the nifedipine-insensitive calcium influx becomes subject to inhibitory regulation by muscarinic receptors. (C) 2001 Elsevier Science B.V. All rig hts reserved.