Evidence for separate effects of U73122 on phospholipase C and calcium channels in human platelets.
U73122 ((1-[6-(( 17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)exyl]-1H-p yrrole-2,5-dione)) is generally used as a selective inhibitor of phospholipase C (PLC) and the related rise in cytosolic Ca2+. Recently, by using hepatocytes, it was suggested that its action sites are different for PLC activation and increase in Ca2+ concentration. To verify whether U73122 has different sites for inhibiting PLC activation and calcium responses in human platelets, aggregation, Mn2+ influx, cytosolic Ca2+ increase and PLC activation were studied in response to thrombin and the synthetic agonist of the thromboxane receptor U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxyprostaglandin F2alpha). With both agonists, U73122 inhibited aggregation, Mn2+ influx and the enhancement of cytosolic calcium at concentrations of 2 microM or lower, while 10 microM was necessary to inhibit PLC activation. Our results suggested that U73122 is much more active in antagonizing Ca2+ channels, both the intracellular ones, which are activated by formation of inositol 1,4,5 P3 and those present on plasma membrane, than in reducing the activation of PLC.
Pulcinelli
F M
FM
Department of Experimental Medicine and Pathology, University La Sapienza, Rome, Italy.
Gresele
P
P
Bonuglia
M
M
Gazzaniga
P P
PP
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000097:blood; D015220:Calcium Channels / Q000097:blood* / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D004963:Estrenes / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000097:blood; D008345:Manganese / Q000097:blood; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000097:blood*
D015220:Calcium Channels; D004963:Estrenes; D010726:Phosphodiesterase Inhibitors; D010975:Platelet Aggregation Inhibitors; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D008345:Manganese; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D002118:Calcium