The nicotinic acetylcholine receptor of the bovine chromaffin cell, a new target for dihydropyridines.
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 microM. The L-type Ca2+ channel activator Bay K 8644 potentiated the uptake of 45Ca2+ induced by K+ depolarization at concentrations between 10 nM and 1 microM, but completely inhibited the uptake of 45Ca2+ by DMPP (IC50, 0.9 microM). 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 microM abolished the depolarization induced by DMPP, leaving the K(+)-evoked depolarization unaffected. Tetrodotoxin (2 microM) did not affect the DMPP- or high K(+)-mediated cell depolarization. Whole-cell inward current evoked by 100 microM DMPP (IDMPP) was measured in cells voltage-clamped at -80 mV. Nimodipine (10 microM) reduced IDMPP by 36%; Bay K 8644 (10 microM) inhibited IDMPP by 67%. DMPP-evoked catecholamine release from superfused chromaffin cells was reduced by over 90% with 10 microM nimodipine; in contrast, K(+)-evoked release was decreased by 20%.(ABSTRACT TRUNCATED AT 250 WORDS)
López
M G
MG
Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Fonteríz
R I
RI
Gandía
L
L
de la Fuente
M
M
Villarroya
M
M
García-Sancho
J
J
García
A G
AG
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology*; D004246:Dimethylphenylpiperazinium Iodide / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004594:Electrophysiology; D004759:Enterochromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D016257:Fura-2 / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009553:Nimodipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011950:Receptors, Cholinergic / Q000187:drug effects*
D002132:Calcium Radioisotopes; D002395:Catecholamines; D004095:Dihydropyridines; D011950:Receptors, Cholinergic; D008345:Manganese; D004246:Dimethylphenylpiperazinium Iodide; D009553:Nimodipine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011188:Potassium; D002118:Calcium; D016257:Fura-2