title: Suppression by phospholipase A2 inhibitors of secretion of catecholamines from isolated adrenal medullary cells by suppression of cellular calcium uptake.
abstract: The involvement of phospholipase A2 in the secretion of catecholamines and cellular uptake of 45Ca2+ was investigated in isolated bovine adrenal medullary cells. In these cells, stimulation of cholinergic receptors by carbamylcholine causes the activation of receptor-linked Ca-channels and influx of Ca2+ is known to trigger the secretory process. Phospholipase A2 inhibitors, such as quinacrine, chloroquine, quinine and p-bromophenacyl bromide, all inhibited the secretion of catecholamines evoked by carbamylcholine in a dose-dependent manner. These phospholipase A2 inhibitors also inhibited the cellular uptake of 45Ca2+ evoked by carbamylcholine with similar dose-response curves to those for inhibition of catecholamine secretion. The inhibition by phospholipase A2 inhibitors was found to be distinct from inhibition by d-tubocurarine which competitively blocks acetylcholine receptors, and from inhibition by diltiazem which acts as a Ca-antagonist at Ca-channels. Phospholipase A2 inhibitors seem to suppress the secretion of catecholamines by interfering with the linkage between acetylcholine receptors and Ca-channels by the membrane effects including the inhibition of endogenous phospholipase A2 activity of the adrenal medullary cells.
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002738:Chloroquine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D010740:Phospholipases / Q000037:antagonists & inhibitors*; D010741:Phospholipases A / Q000037:antagonists & inhibitors*; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology
chemical_list: D000098:Acetophenones; D002395:Catecholamines; D002738:Chloroquine; D002217:Carbachol; D011803:Quinine; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine; C006821:4-bromophenacyl bromide; D002118:Calcium