title: Effect of activation of muscarinic receptors on intracellular free calcium and secretion in bovine adrenal chromaffin cells.
abstract: Stimulation of the nicotinic receptor of bovine chromaffin cells results in a rise in intracellular free calcium [( Ca2+]i) and subsequent release of catecholamine. This response is totally dependent on the presence of external Ca2+. Monitoring [Ca2+]i using quin-2 demonstrated a rise in [Ca2+]i in response to muscarinic agonists which was approximately 4-times less than that obtained in response to nicotinic stimulation. This atropine-sensitive [Ca2+]i rise occurred after a 10-s lag and was found to be independent of the external Ca2+, implying the existence of an intracellular Ca2+ source. Despite producing this [Ca2+]i rise low concentrations of the muscarinic agonist, methacholine (under 1 X 10(-3) M), failed to trigger secretion itself and did not effect the secretory response elicited by nicotine. Challenging the cells with higher methacholine concentrations (over 1 X 10(-3) M) resulted in the same [Ca2+]i rise, no secretion, but an inhibition of secretion due to nicotine. This latter response, however, was found to be atropine-insensitive and therefore non-muscarinic. The [Ca2+]i rise and secretion due to depolarization by 55 mM K+ were largely unaffected by prior addition 1 X 10(-2) M methacholine, inferring that high concentrations of methacholine inhibit nicotine-induced secretion by interacting with the nicotinic receptor. These results provide evidence consistent with the existence of an intracellular Ca2+ store mobilized by muscarinic receptor activation in bovine chromaffin cells and show that, despite causing a rise in [Ca2+]i, bovine chromaffin cell muscarinic stimulation does not effect secretion itself or secretion induced by either nicotine or high K+.
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000634:Aminoquinolines; D002395:Catecholamines; D008688:Methacholine Compounds; D011976:Receptors, Muscarinic; D016210:Methacholine Chloride; D009538:Nicotine; C035739:Quin2; D011188:Potassium; D002118:Calcium