title: Mechanism of dopamine mediated inhibition of neuropeptide Y release from pheochromocytoma cells (PC12 cells).
abstract: In rat pheochromocytoma (PC12) cells the dopamine D(2) receptor agonists apomorphine (APO) and n-propylnorapomorphine (NPA) produced a concentration dependent inhibition of K(+)-evoked neuropeptide Y release (NPY-ir). The effect of APO was blocked by the dopamine D(2)-receptor antagonist, eticlopride, but not the D(1)/D(3) or the D(4)/D(2) antagonists, SCH23390 or clozapine, respectively. The D(1)/D(5) receptor agonist, SKF38393 or the D(3) agonists PD128907 and 7-OH DPAT had no effect. Selective N and L-type voltage gated Ca(2+) channel blockers, omega-conotoxin GVIa (Ctx-GVIa) and nifedipine, respectively, produced a concentration dependent inhibition of NPY-ir release but were not additive with APO. The Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) II inhibitor KN-62 produced a concentration-dependent inhibition of NPY-ir release but the combination of KN-62 and APO produced no further inhibition. PMA-mediated protein kinase C stimulation significantly increased both basal and K(+)-evoked release of NPY-ir, and in the presence of PMA APO had no inhibitory effect. The PKC antagonist, chelerythrine, inhibited K(+)-evoked NPY-ir release but was not additive with APO. Neither forskolin-mediated adenylate cyclase activation and the active cAMP analog Sp-cAMPS, nor the adenylate cyclase inhibitor SQ 22536, and the competitive inhibitor of cAMP-dependent protein kinases Rp-cAMPS, had any significant effect on K(+)-evoked NPY-ir release. This suggests the inhibitory effect of APO on K(+)-evoked release of NPY-ir from PC12 cells is most likely mediated through activation of dopamine D(2) receptors leading to direct inhibition of N and L-type voltage gated Ca(2+) channels, or indirect inhibition of PKC, both of which would reduce [Ca(2+)](i) and inactivate CaM kinase.
authors.affiliation: Department of Pharmaceutical Sciences, Massachusetts College of Pharmacy and Health Sciences, School of Pharmacy-Worcester, 19 Foster Street, Worcester, MA 01608, United States.
authors.forename: Guihua
authors.initials: G
authors.lastname: Cao
authors.forename: Alice
authors.initials: A
authors.lastname: Gardner
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Westfall
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000310:Adrenal Gland Neoplasms / Q000473:pathology; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002417:Cattle; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004347:Drug Interactions; D009478:Neuropeptide Y / Q000378:metabolism*; D016716:PC12 Cells; D037342:Pertussis Toxin / Q000494:pharmacology; D010673:Pheochromocytoma / Q000473:pathology*; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D051381:Rats
chemical_list: D015220:Calcium Channels; D018492:Dopamine Antagonists; D009478:Neuropeptide Y; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517599:Camk1 protein, rat; C517682:Pnck protein, rat; D000262:Adenylyl Cyclases; D001058:Apomorphine; D004298:Dopamine