Abstract: | The involvement of cAMP- andCa2+-mediated pathways in theactivation of tyrosine hydroxylase (TH) gene expression by nicotine wasexamined in PC-12 cells. ExtracellularCa2+ and elevations inintracellular Ca2+ concentration(Ca2+]i)were required for nicotine to increase TH mRNA. The nicotine-elicited rapid rise inCa2+]iwas inhibited by blockers of either L-type or N-type, and to a lesserextent P/Q-, but not T-type, voltage-gatedCa2+ channels. With continualnicotine treatment,Ca2+]ireturned to basal levels within 3-4 min. After a lag of~5-10 min, there was a smaller elevation inCa2+]ithat persisted for 6 h and displayed different responsiveness toCa2+ channel blockers. This secondphase of elevatedCa2+]iwas blocked by an inhibitor of store-operatedCa2+ channels, consistent with theobserved generation of inositol trisphosphate.1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), when added before or 2 h after nicotine,prevented elevation of TH mRNA. Nicotine treatment significantly raised cAMP levels. Addition of the adenylyl cyclase inhibitor2',5'-dideoxyadenosine (DDA) prevented thenicotine-elicited phosphorylation of cAMP response element bindingprotein. DDA also blocked the elevation of TH mRNA only when addedafter the initial transient rise in Ca2+]iand not after 1 h. This study reveals that several temporal phases areinvolved in the induction of TH gene expression by nicotine, each ofthem with differing requirements forCa2+ and cAMP. |