Three Distinct Ca2+Influx Pathways Couple Acetylcholine Receptor Activation to Catecholamine Secretion from PC12 Cells

Abstract:Amperometry and microfluorimetry were employed to investigate the Ca2+‐dependence of catecholamine release induced from PC12 cells by cholinergic agonists. Nicotine‐evoked exocytosis was entirely dependent on extracellular Ca2+but was only partly blocked by Cd2+, a nonselective blocker of voltagegated Ca2+channels. Secretion and rises of [Ca2+]iobserved in response to nicotine could be almost completely blocked by methyllycaconitine and α‐bungarotoxin, indicating that such release was mediated by receptors composed of α7 nicotinic acetylcholine receptor subunits. Secretion and [Ca2+]irises 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 caffeine‐sensitive intracellular store, and release from this store induced capacitative Ca2+entry that could be blocked by La3+and Zn2+. This Ca2+entry pathway mediated all secretion evoked by muscarine. Thus, activation of acetylcholine receptors stimulated rises of [Ca2+]iand exocytosis via Ca2+influx through voltage‐gated Ca2+channels, α7 subunit‐containing nicotinic acetylcholine receptors, and channels underlying capacitative Ca2+entry.