Pertussis toxin inhibits alpha 2-adrenoceptor-mediated inhibition of adenylate cyclase without affecting muscarinic regulation of [Ca2+]i or inositol phosphate generation in SH-SY5Y human neuroblastoma cells.

The present study reports the differential effects of pertussis toxin on muscarinic regulation of intracellular Ca2+ and inositol phosphate generation and alpha 2-adrenoceptor-mediated inhibition of cAMP formation in SH-SY5Y human neuroblastoma cells. Carbachol caused a biphasic increase in intracellular Ca2+ (release of internal stores and Ca2+ entry) and a dose-dependent increase in inositol phosphate formation. Pertussis toxin pretreatment did not affect either of these components of the signal transduction pathway but did completely reverse the alpha 2-adrenoceptor-mediated inhibition of forskolin-stimulated cAMP formation. These data indicate that muscarinic regulation of inositol phosphate generation occurs via a pertussis toxin-insensitive G-protein and that Ca2+ entry in these cells may not occur via a G-protein.