Calcium signalling mediated through α7 and non‐α7 nAChR stimulation is differentially regulated in bovine chromaffin cells to induce catecholamine release
Open Access
- 14 September 2010
- journal article
- Published by Wiley in British Journal of Pharmacology
- Vol. 162 (1), 94-110
- https://doi.org/10.1111/j.1476-5381.2010.01034.x
Abstract
BACKGROUND AND PURPOSE Ca2+ signalling and exocytosis mediated by nicotinic receptor (nAChR) subtypes, especially the α7 nAChR, in bovine chromaffin cells are still matters of debate. EXPERIMENTAL APPROACH 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. KEY RESULTS Minimal [Ca2+]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 [Ca2+]c transients, that were blocked by mecamylamine but were unaffected by α‐bungarotoxin (non‐α7 response). [Ca2+]c increases mediated by α7 nAChR were related to Ca2+ entry through non‐L‐type Ca2+ channels, whereas non‐α7 nAChR‐mediated signals were related to L‐type Ca2+ channels; Ca2+‐induced Ca2+‐release contributed to both responses. Mitochondrial involvement in the control of [Ca2+]c transients, mediated by either receptor, was minimal. Catecholamine release coupled to α7 nAChRs was more efficient in terms of catecholamine released/[Ca2+]c. CONCLUSIONS AND IMPLICATIONS [Ca2+]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.Keywords
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