Unmasking the functions of the chromaffin cell alpha7 nicotinic receptor by using short pulses of acetylcholine and selective blockers.
Methyllycaconitine (MLA), alpha-conotoxin ImI, and alpha-bungarotoxin inhibited the release of catecholamines triggered by brief pulses of acetylcholine (ACh) (100 microM, 5 s) applied to fast-superfused bovine adrenal chromaffin cells, with IC50s of 100 nM for MLA and 300 nM for alpha-conotoxin ImI and alpha-bungarotoxin. MLA (100 nM), alpha-conotoxin ImI (1 microM), and alpha-bungarotoxin (1 microM) halved the entry of 45Ca2+ stimulated by 5-s pulses of 300 microM ACh applied to incubated cells. These supramaximal concentrations of alpha7 nicotinic receptor blockers depressed by 30% (MLA), 25% (alpha-bungarotoxin), and 50% (alpha-conotoxin ImI) the inward current generated by 1-s pulses of 100 microM ACh, applied to voltage-clamped chromaffin cells. In Xenopus oocytes expressing rat brain alpha7 neuronal nicotinic receptor for acetylcholine nAChR, the current generated by 1-s pulses of ACh was blocked by MLA, alpha-conotoxin ImI, and alpha-bungarotoxin with IC50s of 0.1 nM, 100 nM, and 1.6 nM, respectively; the current through alpha3 beta4 nAChR was unaffected by alpha-conotoxin ImI and alpha-bungarotoxin, and weakly blocked by MLA (IC50 = 1 microM). The functions of controlling the electrical activity, the entry of Ca2+, and the ensuing exocytotic response of chromaffin cells were until now exclusively attributed to alpha3 beta4 nAChR; the present results constitute the first evidence to support a prominent role of alpha7 nAChR in controlling such functions, specially under the more physiological conditions used here to stimulate chromaffin cells with brief pulses of ACh.
López
M G
MG
Departamento de Farmacología, Facultad de Medicina, Instituto de Farmacología Teófilo Hernando, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, 28029 Madrid, Spain.
Montiel
C
C
Herrero
C J
CJ
García-Palomero
E
E
Mayorgas
I
I
Hernández-Guijo
J M
JM
Villarroya
M
M
Olivares
R
R
Gandía
L
L
McIntosh
J M
JM
Olivera
B M
BM
García
A G
AG
D000109:Acetylcholine / Q000494:pharmacology*; D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002038:Bungarotoxins / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D018678:Cholinergic Agents / Q000494:pharmacology*; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D020916:Conotoxins; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008978:Mollusk Venoms / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002038:Bungarotoxins; D018678:Cholinergic Agents; C579165:Chrna7 protein, rat; D020916:Conotoxins; D008978:Mollusk Venoms; D018733:Nicotinic Antagonists; D009842:Oligopeptides; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C087686:alpha-conotoxin ImI; C054634:methyllycaconitine; D000109:Acetylcholine; D002118:Calcium; D000157:Aconitine