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A choline‐evoked [Ca 2+ ] C signal causes catecholamine release and hyperpolarization of chromaffin cells
Author(s) -
Fuentealba Jorge,
Olivares Román,
Alés Eva,
Tapia Laura,
Rojo Jonathan,
Arroyo Gloria,
Aldea Marcos,
Criado Manuel,
Gandía Luis,
García Antonio G.
Publication year - 2004
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.04-1828fje
Subject(s) - chromaffin cell , hyperpolarization (physics) , acetylcholine , choline , chemistry , catecholamine , biophysics , depolarization , medicine , endocrinology , cholinergic , adrenal medulla , biology , biochemistry , stereochemistry , nuclear magnetic resonance spectroscopy
In bovine chromaffin cells fast‐superfused with Krebs‐HEPES solution containing 1–2 mM Ca 2+ , 5 s pulses of choline (1–10 mM), elicited catecholamine secretory responses that were only ~10% of those evoked by ACh (0.01–0.1 mM). However, in high‐Ca 2+ solutions (10–20 mM) the size of the choline secretory responses approached those of ACh. The choline responses (10 mM choline in 20 mM Ca 2+ , 10Cho/20Ca 2+ ) tended to decline upon repetitive pulsing, whereas those of ACh were well maintained. The confocal [Ca 2+ ] c increases evoked by 10Cho/20Ca 2+ were similar to those of ACh. Whereas 10Cho/20Ca 2+ caused mostly hyperpolarization of chromaffin cells, 0.1ACh/20 Ca 2+ caused first depolarization and then hyperpolarization; in regular solutions (2 mM Ca 2+ ), the hyperpolarizing responses did not show up. In Xenopus oocytes injected with mRNA for bovine α7 nicotinic receptors (nAChRs), 10Cho/20 Ca 2+ fully activated an inward current; in oocytes expressing α3β4, however, the inward current elicited by choline amounted to only 4% of the size of α7 current. Our results suggest that choline activates the entry of Ca 2+ through α7 nAChRs; this leads to a cytosolic concentration of calcium ([Ca 2+ ] c ) rise that causes the activation of nearby Ca 2+ ‐dependent K + channels and the hyperpolarization of the chromaffin cell. This response, which could be unmasked provided that cells were stimulated with high‐Ca 2+ solutions, may be the underlying mechanism through which choline exerts a modulatory effect on the electrical activity of the chromaffin cell and on neurotransmitter release at cholinergic synapses.