title: Biscoclaurine alkaloids inhibit receptor-mediated phospholipase A2 activation probably through uncoupling of a GTP-binding protein from the enzyme in rat peritoneal mast cells.
abstract: The mechanism underlying the inhibitory effect of biscoclaurine (bisbenzylisoquinoline) alkaloids on phospholipase A2 activation in the signalling system of stimulated rat peritoneal mast cells was studied. Cepharanthine, berbamine and isotetrandrine inhibited antigen- and compound 48/80-induced arachidonic acid liberation, but not diacylglycerol formation or histamine release. They had no effect on A23187-induced arachidonic acid liberation, which was prevented by p-bromophenacyl bromide, a known phospholipase A2 inhibitor, and also did not affect phospholipase A2 activity in a cell-free system including an exogenous phospholipid substrate. Each alkaloid also inhibited arachidonic acid liberation induced by guanosine 5'-O-(3-thiotriphosphate) in saponin-permeabilized mast cells, and by mastoparan or NaF plus AlCl3 intact cells. Furthermore, each alkaloid abolished the inhibitory effect of islet-activating protein on the compound 48/80-induced arachidonic acid liberation. These data suggest that these alkaloids suppress the receptor-mediated phospholipase A2 activation through, at least in part, uncoupling of a GTP-binding protein from the enzyme, rather than by affecting the enzyme directly.
authors.affiliation: Department of Biochemistry, Kyoto Pharmaceutical University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Akiba
authors.forename: E
authors.initials: E
authors.lastname: Kato
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Fujii
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D044182:Benzylisoquinolines; D000001:Calcimycin / Q000494:pharmacology; D004140:Dinitrophenols / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006632:Histamine / Q000378:metabolism; D050356:Lipid Metabolism; D008297:Male; D008407:Mast Cells / Q000187:drug effects* / Q000201:enzymology; D010537:Peritoneum; D037342:Pertussis Toxin; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D011919:Rats, Inbred Strains; D012710:Serum Albumin, Bovine / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology; D052117:Benzodioxoles
chemical_list: D000470:Alkaloids; D016718:Arachidonic Acid; D044182:Benzylisoquinolines; D000001:Calcimycin; D004140:Dinitrophenols; D019204:GTP-Binding Proteins; D006632:Histamine; D037342:Pertussis Toxin; D010741:Phospholipases A; D054467:Phospholipases A2; D012710:Serum Albumin, Bovine; D010566:Virulence Factors, Bordetella; D003189:p-Methoxy-N-methylphenethylamine; C034638:dinitrophenyl-bovine serum albumin; C006947:cepharanthine; D052117:Benzodioxoles; C027870:berbamine