M. Mahata et al., PROADRENOMEDULLIN N-TERMINAL-20 PEPTIDE - MINIMAL ACTIVE-REGION TO REGULATE NICOTINIC RECEPTORS, Hypertension, 32(5), 1998, pp. 907-916
Proadrenomedullin N-terminal 20 peptide (PAMP-[1-20]; ARLDVASEFRKKWNKW
ALSR-amide) is a potent hypotensive and catecholamine release-inhibito
ry peptide released from chromaffin cells. We studied the mechanism of
PAMP action and how its function is linked to structure. We tested hu
man PAMP-[1-20] on catecholamine secretion in PC12 pheochromocytoma ce
lls and found it to be a potent, dose-dependent (IC50 approximate to 3
50 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 (Na-22(
+),Ca-45(2+)) signal transduction was disrupted by this peptide, and p
otencies for inhibition of Na-22(+) uptake and catecholamine secretion
were comparable. Even high-dose nicotine failed to overcome the inhib
ition, suggesting noncompetitive nicotinic antagonism. N- and C-termin
al 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 block
ed (EC50 approximate to 270 nmol/L) nicotinic cholinergic agonist dese
nsitization of catecholamine release, as well as desensitization of ni
cotinic signal transduction (Na-22(+) uptake). Thus, PAMP may exert bo
th inhibitory and facilitatory effects on nicotinic signaling, dependi
ng on the prior state of nicotinic stimulation. PAMP may therefore con
tribute to a novel, autocrine, homeostatic (negative-feedback) mechani
sm controlling catecholamine release.