Portal de Periódicos da CAPES

The nicotinic acetylcholine receptor of the bovine chromaffin cell, a new target for dihydropyridines

1993; Elsevier BV; Volume: 247; Issue: 2 Linguagem: Inglês

10.1016/0922-4106(93)90078-n

1872-8251

Manuela G. López, Rosalba I. Fonteríz, Luis Gandı́a, Maite de la Fuente, Mércedes Villarroya, Javier García‐Sancho, Antonio G. Garcı́a,

Cardiac electrophysiology and arrhythmias

The effects of 1,4-dihydropyridine derivatives on divalent cation transients and catecholamine release stimulated by either high K+ or the nicotinic receptor agonist dimethyl-phenyl-piperazinium (DMPP) have been compared in bovine adrenal chromaffin cells. The activation of Ca2+ entry pathways was followed by measuring 45Ca2+ or Mn2+ uptake, or by the changes of [Ca2+]i in fura-2-loaded chromaffin cells. Various dihydropyridine Ca2+ channel blockers (nimodipine, PCA50938, nifedipine, nitrendipine, furnidipine) abolished the DMPP-mediated effects, but prevented only partially the activation by high [K+]0 of 45Ca2+ uptake. The IC50 for DMPP-induced activation was around 1 μM. The L-type Ca2+ channel activator Bay K 8644 potentiated the uptake of 45Ca+ induced by K++ depolarization at concentrations between 10 nM and 1 μM, but completely inhibited the uptake of 45Ca2+ by DMPP (IC50, 0.9 μM). Both high [K+]0 and DMPP produced membrane depolarization as measured using bis-oxonol. The DMPP-evoked, but not the K+-evoked membrane depolarization was prevented by Na+ removal, suggesting that the depolarization was due to Na+ entry through the acetylcholine receptor ionophore. Nimodipine at 10 μM abolished the depolarization induced by DMPP, leaving the K+-evoked depolarization unaffected. Tetrodotoxin (2 μM) did not affect the DMPP- or high K+-mediated cell depolarization. Whole-cell inward current evoked by 100 μM DMPP (IDMPP) was measured in cells voltage-clamped at −80 mV. Nimodipine (10 μM) reduced IDMPP by 36%; Bay K 8644 (10 μM) inhibited IDMPP by 67%. DMPP-evoked catecholamine release from superfused chromaffin cells was reduced by over 90% with 10 μM nimodipine; in contrast, K+-evoked release was decreased by 20%. The results suggest that the nicotinic acetylcholine receptor of bovine chromaffin cells contains a site for dihydropyridines whose occupation blocks Na+ entry through the receptor ionophore. This chromaffin cells contains a site for dihydropyridines whose occupation blocks Na+ entry through the receptor ionophre. This limits the ensuing membrane depolarization, firing of action potentials, recruitment of Ca2+ channels and entry of Ca2+ in the cells, leading to a decrease in catecholamine secretion.