Component of nicotine-induced intracellular calcium elevation mediated through α3- and α5-containing nicotinic acetylcholine receptors are regulated by cyclic AMP in SH-SY 5Y cells

The pathway from the medial habenular nucleus to the interpeduncular nucleus, in which nicotinic acetylcholine receptor (nAChR) including the α3 and α5 subunits (α3 * and α5 * nAChRs) are expressed, is implicated in nicotine dependence. We investigated whether α3 * and α5 * nAChRs are regulated by cAMP using SH-SY5Y cells to clarify the significance of these receptors in nicotine dependence. We analyzed the nicotine-induced elevation of intracellular Ca(2+) ([Ca(2+)]i). Nicotine induces a concentration-dependent increase in [Ca(2+)]i. The elimination of Ca(2+) from extracellular fluid or intracellular stores demonstrated that the nicotine-induced [Ca(2+)]i elevation was due to extracellular influx and intracellular mobilization. The effects of tubocurarine on nicotine-induced [Ca(2+)]i elevation and current suggest that intracellular mobilization is caused by plasma membrane-permeating nicotine. The inhibition of α3 *, α5 *, α7 nAChR and voltage-gated Ca(2+) channels by using siRNAs and selective antagonists revealed the involvement of these nAChR subunits and channels in nicotine-induced [Ca(2+)]i elevation. To distinguish and characterize the α3 * and α5 * nAChR-mediated Ca(2+) influx, we measured the [Ca(2+)]i elevation induced by nonmembrane-permeating acetylcholine when muscarinic receptors, α7nAChR and Ca(2+) channels were blocked. Under this condition, the [Ca(2+)]i elevation was significantly inhibited with a 48-h treatment of dibutyryl cAMP, which was accompanied by the downregulation of α3 and β4 mRNA. These findings suggest that α3 * and α5 * nAChR-mediated Ca(2+) influx is possibly regulated by cAMP at the transcriptional level.