title: Cation channel activated by muscarinic agonists on porcine adrenal chromaffin cells.
abstract: A large portion (70%) of the secretory response to muscarinic agonists in porcine adrenal chromaffin cells has previously been shown to be dependent on extracellular Ca2+ (Xu et al., J. Neurochem. 56: 1899-1896, 1991). Results presented here show that muscarinic agonists activate a cation-selective channel which is permeable to divalent cations. The muscarinic agonist, methacholine, was found to activate the uptake of Mn2+, which paralleled the ability of methacholine to activate 45Ca2+ uptake as shown previously. Secretion induced by methacholine was not affected by nifedipine, a compound that inhibits dihydropyridine-sensitive voltage-gated Ca2+ channels. In voltage-clamped cells, methacholine activated whole cell currents, which reversed at approximately -20 mV in standard salt solutions. However, with the standard whole cell configuration, the currents were slow to activate and were often erratic. In contrast, when the perforated-patch (nystatin) technique was used to measure whole cell currents, methacholine rapidly activated sustained inward currents. Ion-substitution experiments indicated that the inward currents were carried by Na+, Ba2+, or Ca2+ but not by Cl-. Single-channel currents activated by methacholine were observed in outside-out vesicles, which were electrically accessed using the perforated-patch technique. These channels reversed at -15 mV, had a slope conductance of 20 pS, and were 14-fold more likely to be open in the presence of methacholine. These channels are probably responsible for the extracellular Ca(2+)-dependent secretory response to muscarinic receptor stimulation in porcine adrenal chromaffin cells.
authors.affiliation: Department of Physiology, University of Wisconsin Medical School, Madison 53706, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Forsberg
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
mesh_terms: D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism; D002412:Cations / Q000378:metabolism*; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004594:Electrophysiology; D016257:Fura-2; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism*; D008345:Manganese / Q000502:physiology; D016210:Methacholine Chloride / Q000494:pharmacology; D009116:Muscarine / Q000819:agonists*; D011976:Receptors, Muscarinic / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D002395:Catecholamines; D002412:Cations; D007473:Ion Channels; D011976:Receptors, Muscarinic; D016210:Methacholine Chloride; D008345:Manganese; D009116:Muscarine; D002118:Calcium; D016257:Fura-2; D014403:Tubocurarine