Mediation of the depolarization-induced [ca2+]i increase in rat sublingual acini by acetylcholine released from nerve terminals

In sublingual mucous acini, membrane depolarization induces a threefold transient increase in cytosolic free Ca2+ concentration ([Ca2+]i). The underlying mechanism was examined by using the Call-sensitive fluorescent indicator fura-2. Membrane depolarization with high K + induced a transient [Ca2+]i increase in acini, but not in single acinar cells. Atropine, pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide prevented the [Ca2+]i increase, suggesting the involvement of muscarinic receptor activation. Inhibition of the inositol trisphosphate OP,)-sensitive Ca2+ release pathway with 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate prevented the depolarization-induced increase in [Ca2+]i. Blockade of nicotinic receptors and L-, N-, and P-type voltage-dependent Ca2+ channels (hexamethonium, nifedipine, diltiazem, ω-conotoxin GVIA and ω-agatoxin IVA) did not inhibit the increase in [Ca2+]i. However, Cd2+ (0.2 mM) blocked > 85% of the [Ca2+]i increase. The depolarizationinduced [Ca2+]i increase was also extracellular Ca2+-dependent. These results suggest that the membrane depolarization-induced Ca2+ increase in sublingual acini is mediated by activating Cd2+-sensitive, voltage-dependent Ca2+ channels in nerve terminals associated with the dispersed acini and stimulating release of acetylcholine, which then triggers the [Ca2+]i increase in acinar cells.