title: Multiple calcium channels are required for pituitary adenylate cyclase-activating polypeptide-induced catecholamine secretion from bovine cultured adrenal chromaffin cells.
abstract: The effects of L-, N-, P- and Q-type calcium channel antagonists and (+/-)-BayK-8644 on catecholamine release induced by pituitary adenylate cyclase-activating polypeptide (PACAP-27) were investigated in bovine cultured adrenal chromaffin cells. PACAP-27 induced the release of 4-15% of the total cellular catecholamines over 7 min, with an EC50 of 20 nM and the effect approaching maximum at 100 nM. Catecholamine release was fully dependent on the presence of extracellular calcium. The dihydropyridine nitrendipine which inhibits L-type calcium channels inhibited PACAP-27-induced secretion in a concentration dependent manner with an inhibition of 20-30% at 1 microM. In contrast, (+/-)-BayK-8644, which prolongs the opening of L-type calcium channels produced a concentration-dependent increase in PACAP-27-induced catecholamine release with 1 microM increasing release by 40-60%. Blockade of N-type calcium channels with omega-conotoxin GVIA reduced release by 5-15%. Block of P-type channels with low concentrations of omega-agatoxin IVA (< or = 30 nM) had no significant effect on release, while higher concentrations (100-300 nM) which block Q-type channels reduced release by up to 15%. omega-Conotoxin MVIIC, an antagonist of Q-type calcium channels and also of N- and P-type channels, inhibited release in a concentration-dependent manner with a near maximum effect of 30-50% produced by 300 nM. The combination of omega-conotoxin GVIA and omega-agatoxin IVA reduced release by 40-50%. Addition of omega-conotoxin MVIIC (300 nM) to the combination of omega-conotoxin GVIA (10 nM) and omega-agatoxin IVA (100 nM) did not inhibit catecholamine release more than with omega-conotoxin GVIA and omega-agatoxin IVA alone, indicating that 100 nM omega-agatoxin IVA was sufficient to block the Q-type calcium channels. When nitrendipine was used together with omega-conotoxin GVIA, omega-agatoxin IVA and omega-conotoxin MVIIC, catecholamine release induced by 20 nM or 100 nM PACAP-27 was reduced by 70-85%. Taken together these results suggest that influx of calcium through multiple different voltage-sensitive calcium channels mediate PACAP-27-induced catecholamine release from bovine chromaffin cells, and that L-, N- and Q-channels contribute to this response.
authors.affiliation: Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: M
authors.initials: M
authors.lastname: O'Farrell
authors.forename: P D
authors.initials: PD
authors.lastname: Marley
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D009479:Neuropeptides / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000502:physiology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide
chemical_list: D002120:Calcium Channel Agonists; D015220:Calcium Channels; D002395:Catecholamines; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester