Internal Ca2+ mobilization by muscarinic stimulation increases secretion from adrenal chromaffin cells only in the presence of Ca2+ influx.
The cytosolic free Ca2+ concentration ([Ca2+]in) in single cat and bovine adrenal chromaffin cells was measured to determine whether or not there was any correlation between the [Ca2+]in and the catecholamine (CA) secretion caused by muscarinic receptor stimulation. In cat chromaffin cells, methacholine (MCh), a muscarinic agonist, raised [Ca2+]in by activating both Ca2+ influx and intracellular Ca2+ mobilization with an accompanying CA secretion. In bovine cells, MCh elevated [Ca2+]in by mobilizing intracellular Ca2+ but did not cause CA secretion. The MCh-induced rise in [Ca2+]in in cat cells was much higher than that in bovine cells, but when Ca2+ influx was blocked, the rise was reduced, with a concomitant loss of secretion, to a level comparable to that in bovine cells. Intracellular Ca2+ mobilization due to muscarinic stimulation substantially increased secretion from depolarized bovine and cat cells, where a [Ca2+]in elevated above basal values was maintained by a continuous Ca2+ influx. These results show that Ca2+ released from internal stores is not effective in triggering secretion unless Ca2+ continues to enter across the plasma membrane, a conclusion suggesting that secretion depends on [Ca2+]in in a particular region of the cell.
Yamagami
K
K
Department of Physiology, Kagoshima University, School of Medicine, Japan.
Nishimura
S
S
Sorimachi
M
M
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000494:pharmacology; D002415:Cats; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D005711:Gallopamil / Q000494:pharmacology; D007700:Kinetics; D016210:Methacholine Chloride / Q000494:pharmacology*; D009116:Muscarine / Q000494:pharmacology*; D009538:Nicotine / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology
D002395:Catecholamines; D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D010862:Pilocarpine; D016210:Methacholine Chloride; D005711:Gallopamil; D010890:Pirenzepine; D009538:Nicotine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D001285:Atropine; D009116:Muscarine; C048593:otenzepad; D002118:Calcium