Mediation of the depolarization-induced [ca 2+] i increase in rat sublingual acini by acetylcholine released from nerve terminals

Abstract

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