Nicotine increases [Ca2+]i in rat sublingual mucous acini by stimulating neurotransmitter release from presynaptic terminals.
The effects of nicotine on the intracellular free Ca2+ concentration ([Ca2+]i) were examined using the Ca(2+)-sensitive fluorescent dyes indo-1 and fura-2 in isolated rat sublingual mucous acini. Nicotine induced a dose-dependent increase in [Ca2+]i. In contrast to the muscarinic agonist carbachol-induced rise in [Ca2+]i, the nicotine-stimulated increase was abolished in a Ca(2+)-free medium, in the presence of L-type Ca2+ channel blockers (diltiazem and D888), by depolarization (high extracellular K+), and if the intracellular Ca2+ pool was first depleted with thapsigargin, an endoplasmic Ca(2+)-ATPase inhibitor. Furthermore, inhibitors of the nicotine acetylcholine receptor (mecamylamine, decamethonium, hexamethonium, tubocurarine, and alpha-bungarotoxin) blocked the nicotine-stimulated increase in [Ca2+]i without affecting the muscarinic-stimulated [Ca2+]i increase, whereas, muscarinic antagonists (atropine, pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide [4-DAMP]) inhibited both the nicotine- and carbachol-induced [Ca2+]i increases. Nicotine stimulation increased inositol 1,4,5-trisphosphate (IP3) content by 50%. Inhibition of the IP3-sensitive intracellular Ca2+ release pathway with 8-(diethylamino)-ocytl-3,4,5-trimethoxybenzoate (TMB-8) prevented the nicotine-induced increase in [Ca2+]i. Confocal imaging of [Ca2+]i indicated that the nicotine-induced and the carbachol-induced increases in [Ca2+]i occurred in the same cells within an acinus. However, in single sublingual acinar cells nicotine did not increase [Ca2+]i, whereas, carbachol did. Taken together, these results suggest that nicotine first triggers the release of acetylcholine from presynaptic nerve terminals associated with the dispersed sublingual acini which then activates muscarinic receptors.
Zhang
G H
GH
Department of Dental Research, University of Rochester, New York 14642.
Melvin
J E
JE
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D009061:Mouth Mucosa / Q000187:drug effects / Q000378:metabolism*; D018727:Muscarinic Antagonists; D009538:Nicotine / Q000494:pharmacology*; D018733:Nicotinic Antagonists; D051381:Rats; D017208:Rats, Wistar; D013361:Sublingual Gland / Q000378:metabolism*
D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D009538:Nicotine; D015544:Inositol 1,4,5-Trisphosphate; D000109:Acetylcholine; D002118:Calcium