Muscarinic stimulation of calcium influx and norepinephrine release in PC12 cells

Muscarinic cholinergic receptor stimulation evokes catecholamine secretion from some cell types, but the mechanism has not been well characterized. Using pheochromocytoma (PC12) cells, we show that the muscarinic agonist methacholine stimulates ⁴⁵Ca²⁺ influx and [³H]norepinephrine release in a dose-dependent manner. Experiments performed in Na⁺-free medium or with inhibitors of voltage-dependent Ca²⁺ channels suggest the involvement of a receptor-activated Ca²⁺ channel which differs significantly from the voltage-dependent Ca²⁺ channel involved in nicotinic receptor-stimulated release. Furthermore, both influx and release were inhibited by pertussis toxin (0.5-2.0 ng/ml, 21 h) with a dose dependency which paralleled the dose dependency of pertussis toxin-dependent in vivo ADP-ribosylation of a 41-kDa protein. These experiments provide the first evidence that muscarinic stimulation evokes neurotransmitter secretion by opening a receptor-activated Ca²⁺ channel which is controlled by a pertussis toxin-sensitive protein.