Verapamil inhibits phosphatidic acid formation and modifies phosphoinositide metabolism in stimulated platelets.
Rabbit platelet-rich plasma was incubated with [32P]orthophosphate, after which the platelets were washed, further incubated in the absence or presence of verapamil and subsequently stimulated with PAF-acether or thrombin. In the absence of verapamil, a rapid increase in radioactivity in phosphatidic acid was observed in platelets stimulated with PAF-acether or thrombin. This was inhibited by verapamil over the concentration range 10(-7) to 10(-4) M, at which concentration the rise in phosphatidic acid was completely abolished. In unstimulated platelets, 10(-4) M verapamil induced an increase in radioactivity in polyphosphoinositides but not significantly in phosphatidylinositol. When these verapamil-treated platelets were stimulated with PAF-acether or thrombin, there was a rapid, sustained loss of the additional radioactivity induced in the polyphosphoinositides by verapamil. Polyphosphoinositide radioactivity remained unchanged in platelets stimulated in the absence of verapamil. Verapamil may stimulate formation of a separate pool of polyphosphoinositide which is susceptible to agonist-induced phospholipase C, and failure to re-synthesize this polyphosphoinositide could result from inhibition of phosphatidic acid synthesis.
Homa
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ST
Department of Chemical Pathology, University College Middlesex School of Medicine, London, U.K.
Khan
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Conroy
D M
DM
Speak
A E
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Smith
A D
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D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003864:Depression, Chemical; D066298:In Vitro Techniques; D008055:Lipids / Q000097:blood; D010712:Phosphatidic Acids / Q000096:biosynthesis*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor / Q000494:pharmacology; D011817:Rabbits; D013917:Thrombin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology*
D008055:Lipids; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor; D014700:Verapamil; D013917:Thrombin