title: Involvement of ion channels in the induction of proenkephalin A gene expression by nicotine and cAMP in bovine chromaffin cells.
abstract: The involvement of Na+ and Ca2+ channels in the stimulatory effect of nicotine and cAMP upon proenkephalin A mRNA (mRNA ENK) levels in primary cultures of bovine adrenal chromaffin cells was analyzed. Nicotine (10 microM) caused about a 2-3-fold increase in mRNA ENK which was abolished by the nicotinic receptor antagonist tubocurarine (4 X 10(-7) M), inhibited by the Ca2+ channel antagonist nifedipine (100 nM) abolished by the Ca2+ channel blocker D600 (10 microM), and augmented by the Ca2+ channel agonist BayK 8644 (100 nM). In contrast, blockade of the Na+ channel by tetrodotoxin (1 microM) did not modulate the nicotine-induced increase in mRNA ENK. Incubation of the cells with forskolin (25 microM) and 8-bromo-cAMP (1 mM) also resulted in an increase in mRNA ENK levels that was inhibited by the Ca2+ channel blocker verapamil (50 microM) and nifedipine (100 nM), whereas it was enhanced by BayK 8644 (100 nM). In addition, the effect of forskolin and 8-bromo-cAMP was decreased by the Na+ channel blocker tetrodotoxin (1 microM). These results suggest that the induction of proenkephalin A gene expression by cAMP and nicotine involves the modulation of ion channels. It appears that changes in Ca2+ flux are involved in mediating this induction. The dihydropyridines nifedipine and BayK 8644 and the Ca2+ channel blockers verapamil and D600 all modulate 45Ca uptake. In addition, we show that incubation of the cells with A23187 (10(-7) M), a Ca2+ ionophore, resulted in an increase in mRNA ENK, indicating that changes in intracellular Ca2+ levels may indeed modulate proenkephalin A gene expression. Although it appears that an elevation of mRNA ENK upon nicotinic receptor activation occurs rapidly (an increase could be detected after 2 h incubation), the findings that the rise in mRNA ENK could be abolished by the Ca2+ channel blocker D600 but not affected by tetrodotoxin (1 microM), and that agents such as KCl (20 mM) and veratridine (5 microM) that increase mRNA ENK by activation of voltage-dependent Ca2+ channels do not result in an increase in intracellular cAMP, provide no evidence for a major role of the adenylate cyclase system in the inducing effect of nicotine upon proenkephalin A gene expression.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004745:Enkephalins / Q000235:genetics*; D005711:Gallopamil / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D007473:Ion Channels / Q000502:physiology*; D009538:Nicotine / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014403:Tubocurarine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D004745:Enkephalins; D007473:Ion Channels; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D005711:Gallopamil; D009538:Nicotine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D012964:Sodium; D014700:Verapamil; D000242:Cyclic AMP; D009543:Nifedipine; D002118:Calcium; D014403:Tubocurarine