Proadrenomedullin N-terminal 20 peptide (PAMP) reduces inward currents and Ca2+ rises induced by nicotine in bovine adrenal medullary cells.

It has been recently reported that proadrenomedullin N-terminal 20 peptide (PAMP), which is secreted with adrenomedullin and catecholamines from the adrenal medulla, inhibits catecholamine release stimulated with nicotine. In the present study, to elucidate anticholinergic mechanisms of PAMP we employed the whole-cell patch-clamp and the intracellular Ca2+ imaging techniques in cultured bovine adrenal medullary cells. PAMP inhibited nicotinic currents and [Ca2+]i rises induced by nicotine in a dose-dependent manner (10(-9)-10(6) M). These inhibitions were selective, since PAMP alone did not induce any ionic currents, moreover it did not affect voltage-dependent Ba2+ currents or high K+ (50 mM)-induced [Ca2+]i rises. The onset of the inhibitory effect of PAMP (10(-6) M) was very rapid and reached a steady-state level within 10 sec. The effect of PAMP (10(-6) M) lasted for about 10-15 min. Desensitization process of the nicotinic current fitted to a single exponential function with a time constant of 6.4 +/- 0.3 sec. When PAMP (10(-6) M) simultaneously added with nicotine (10(-5) M), the desensitization process was facilitated and fitted to two exponentials with time constants of 0.46 +/- 0.08 and 2.5 +/- 0.8 sec. From the present results, the inhibition by PAMP of nicotinic currents which was well associated with that of nicotine induced [Ca2+]i rises leads to the attenuation of catecholamine release probably, at least in part, due to the facilitation of the desensitization process of the nicotinic currents.