Different mechanisms of Ca2+ entry induced by depolarization and muscarinic receptor stimulation in SH-SY5Y human neuroblastoma cells.

Depolarization by elevated K+ and stimulation of muscarinic M3 receptors evoke rises in [Ca2+]i in Fura 2-loaded SH-SY5Y human neuroblastoma cells. The response to K+ (30 and 60 mM) could be inhibited by the dihydropyridine L-channel antagonist +PN 200-110 and totally suppressed by Ni2+, the N-channel blocker omega-conotoxin reduced the response to 60 mM K+. Carbachol-stimulated increase in [Ca2+]i was blocked by atropine and Ni2+ but was totally resistant to the L- and N-channel blockers. This study reveals the presence of L- and N-type voltage-sensitive Ca2+ channels on undifferentiated SH-SY5Y cells that are opened by K+ depolarization but not by muscarinic stimulation.