title: Proadrenomedullin N-terminal 20 peptide: minimal active region to regulate nicotinic receptors.
abstract: Proadrenomedullin N-terminal 20 peptide (PAMP-[1-20]; ARLDVASEFRKKWNKWALSR-amide) is a potent hypotensive and catecholamine release-inhibitory peptide released from chromaffin cells. We studied the mechanism of PAMP action and how its function is linked to structure. We tested human PAMP-[1-20] on catecholamine secretion in PC12 pheochromocytoma cells and found it to be a potent, dose-dependent (IC50 approximately 350 nmol/L) secretory inhibitor. Inhibition was specific for nicotinic cholinergic stimulation since PAMP-[1-20] failed to inhibit release by agents that bypass the nicotinic receptor. Nicotinic cationic (22Na+,45Ca2+) signal transduction was disrupted by this peptide, and potencies for inhibition of 22Na+ uptake and catecholamine secretion were comparable. Even high-dose nicotine failed to overcome the inhibition, suggesting noncompetitive nicotinic antagonism. N- and C-terminal PAMP truncation peptides indicated a role for the C-terminal amide and refined the minimal active region to the C-terminal 8 amino acids (WNKWALSR-amide), a region likely to be alpha-helical. PAMP also blocked (EC50 approximately 270 nmol/L) nicotinic cholinergic agonist desensitization of catecholamine release, as well as desensitization of nicotinic signal transduction (22Na+ uptake). Thus, PAMP may exert both inhibitory and facilitatory effects on nicotinic signaling, depending on the prior state of nicotinic stimulation. PAMP may therefore contribute to a novel, autocrine, homeostatic (negative-feedback) mechanism controlling catecholamine release.
authors.affiliation: Department of Medicine and Center for Molecular Genetics, University of California at San Diego, and San Diego Veterans Affairs Healthcare System, San Diego, CA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Mahata
authors.forename: S K
authors.initials: SK
authors.lastname: Mahata
authors.forename: R J
authors.initials: RJ
authors.lastname: Parmer
authors.forename: D T
authors.initials: DT
authors.lastname: O'Connor
mesh_terms: D053607:Adrenomedullin; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D009538:Nicotine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D010455:Peptides; D010673:Pheochromocytoma / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D002395:Catecholamines; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D010446:Peptide Fragments; D010455:Peptides; D011506:Proteins; D014665:Vasodilator Agents; D053607:Adrenomedullin; D009538:Nicotine; D012964:Sodium; D002118:Calcium