Calcium dependency of muscarinic and nicotinic agonist-induced ATP and catecholamine secretion from porcine adrenal chromaffin cells.
The secretion of catecholamines and ATP induced by cholinergic agonists and its dependence on extracellular Ca2+ were studied in cultured porcine adrenal chromaffin cells. Both nicotine and methacholine (a selective muscarinic agonist) induced secretion and increases in cytosolic free Ca2+ concentration ([Ca2+]in), although the activation of nicotinic receptors produced responses that were larger than those produced by activation of muscarinic receptors. The secretion and the increase in [Ca2+]in evoked by nicotine were completely dependent on extracellular Ca2+ and were blocked by prior depolarization of the cells with high extracellular K+ levels. In addition, nicotine induced significant 45Ca2+ influx. In contrast, the secretion and the increase in [Ca2+]in evoked by methacholine were partially dependent on extracellular Ca2+; methacholine also induced 45Ca2+ influx. Prior depolarization of the cells with high extracellular K+ levels did not block methacholine-induced secretion. In general, nicotinic responses were mediated by Ca2+ influx through voltage-dependent pathways. In contrast, muscarinic responses were dependent on both Ca2+ influx through an unknown mechanism that could not be inactivated by high K+ concentration-induced depolarization and presumably also intracellular Ca2+ mobilization.
Xu
Y P
YP
Department of Physiology, University of Wisconsin Medical School, Madison 53706.
Duarte
E P
EP
Forsberg
E J
EJ
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism*; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004594:Electrophysiology; D010277:Parasympathomimetics / Q000494:pharmacology*; D011976:Receptors, Muscarinic / Q000502:physiology; D011978:Receptors, Nicotinic / Q000502:physiology; D013552:Swine
D015220:Calcium Channels; D002395:Catecholamines; D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D000255:Adenosine Triphosphate; D002118:Calcium