Calcium signalling mediated through α7 and non-α7 nAChR stimulation is differentially regulated in bovine chromaffin cells to induce catecholamine release.
OBJECTIVE
Ca(2+) signalling and exocytosis mediated by nicotinic receptor (nAChR) subtypes, especially the α7 nAChR, in bovine chromaffin cells are still matters of debate.


METHODS
We have used chromaffin cell cultures loaded with Fluo-4 or transfected with aequorins directed to the cytosol or mitochondria, several nAChR agonists (nicotine, 5-iodo-A-85380, PNU282987 and choline), and the α7 nAChR allosteric modulator PNU120596.


RESULTS
Minimal [Ca(2+) ](c) transients, induced by low concentrations of selective α7 nAChR agonists and nicotine, were markedly increased by the α7 nAChR allosteric modulator PNU120596. These potentiated responses were completely blocked by the α7 nAChR antagonist α-bungarotoxin (α7-modulated-response). Conversely, high concentrations of the α7 nAChR agonists, nicotine or 5-iodo-A-85380 induced larger [Ca(2+) ](c) transients, that were blocked by mecamylamine but were unaffected by α-bungarotoxin (non-α7 response). [Ca(2+) ](c) increases mediated by α7 nAChR were related to Ca(2+) entry through non-L-type Ca(2+) channels, whereas non-α7 nAChR-mediated signals were related to L-type Ca(2+) channels; Ca(2+) -induced Ca(2+) -release contributed to both responses. Mitochondrial involvement in the control of [Ca(2+) ](c) transients, mediated by either receptor, was minimal. Catecholamine release coupled to α7 nAChRs was more efficient in terms of catecholamine released/[Ca(2+) ](c) .


CONCLUSIONS
[Ca(2+) ](c) and catecholamine release mediated by α7 nAChRs required an allosteric modulator and low doses of the agonist. At higher agonist concentrations, the α7 nAChR response was lost and the non-α7 nAChRs were activated. Catecholamine release might therefore be regulated by different nAChR subtypes, depending on agonist concentrations and the presence of allosteric modulators of α7 nAChRs.
del Barrio
Laura
L
Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
Egea
Javier
J
León
Rafael
R
Romero
Alejandro
A
Ruiz
Ana
A
Montero
Mayte
M
Alvarez
Javier
J
López
Manuela G
MG
D000494:Allosteric Regulation; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002794:Choline / Q000494:pharmacology; D019439:Chromaffin Cells / Q000378:metabolism*; D005089:Exocytosis; D005456:Fluorescent Dyes; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D064569:alpha7 Nicotinic Acetylcholine Receptor
D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D002395:Catecholamines; D005456:Fluorescent Dyes; D018722:Nicotinic Agonists; C498513:PNU-282987; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D009538:Nicotine; D002794:Choline