Three distinct Ca2+ influx pathways couple acetylcholine receptor activation to catecholamine secretion from PC12 cells

Amperometry and microfluorimetry were employed to investigate the Ca2+-depe ndence of catecholamine release induced from PC12 cells by cholinergic agon ists. Nicotine-evoked exocytosis was entirely dependent on extracellular Ca 2+ but was only partly blocked by Cd2+, a nonselective blocker of voltage-g ated Ca2+ channels. Secretion and rises of [Ca2+], observed in response to nicotine could be almost completely blocked by methyllycaconitine and alpha -bungarotoxin, indicating that such release was mediated by receptors compo sed of alpha 7 nicotinic acetylcholine receptor subunits. Secretion and [Ca 2+](i) rises could also be fully blocked by co-application of Cd2+ and Zn2. Release evoked by muscarine was also fully dependent on extracellular Ca2 +. Muscarinic receptor activation stimulated release of Ca2+ from a caffein e-sensitive intracellular store, and release from this store induced capaci tative Ca2+ entry that could be blocked by La3+ and Zn2+ This Ca2+ entry pa thway mediated all secretion evoked by muscarine, Thus, activation of acety lcholine receptors stimulated rises of [Ca2+](i) and exocytosis via Ca2+ in flux through voltage-gated Ca2+ channels, alpha 7 subunit-containing nicoti nic acetylcholine receptors, and channels underlying capacitative Ca2+ entr y.