Activation of protein kinase C inhibits sodium fluoride-induced elevation of human platelet cytosolic free calcium and thromboxane B 2 generation

Abstract

Addition of NaF to washed platelets produces a dose-dependent and transient elevation of the intracellular free calcium concentration ([Ca ++] i), thromboxane B 2 (TxB 2) generation and dense granule release, all of which are significantly inhibited when the extracellular calcium concentration ([Ca ++] e) is reduced with EGTA. Inhibition of platelet cyclo-oxygenase by acetylsalicylic acid (ASA) does not affect NaF-induced elevation of [Ca ++] i and dense granule release in the presence of 1 mM [Ca ++] e. Pre-incubation of the platelets with the phorbol ester TPA produces a marked inhibition of NaF-induced elevation of [Ca ++] i and TxB 2 generation without affecting dense granule release. Thus, NaF may have more than one site of action. Pretreatment of the platelets with the selective protein kinase C inhibitor H7 prevents TPA induced inhibition of NaF mediated rise in [Ca ++] i and TxB 2 generation. Thus we propose that NaF induced calcium mobilisation is analogous to receptor-operated calcium mobilisation in platelets, as it is readily inhibited by protein kinase C activation or by the reduction of [Ca ++] e and is independent of platelet cyclo-oxygenase activity.