| Abstract: | Addition of NaF to washed platelets produces a dose-dependent and transient elevation of the intracellular free calcium concentration (Ca++]i), thromboxane B2 (TxB2) 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 TxB2 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 TxB2 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. |
