The effects of tyrphostins B42 and B46 on equine platelet function and protein tyrosine phosphorylation

The effects of the protein tyrosine kinase inhibitors tyrphostins B42 and B46 on equine platelet function and protein tyrosine phosphorylation (PTP) were assessed. Tyrphostins B42 and B46 (both at 100 microM concentration) produced significant inhibition of thrombin-stimulated equine platelet aggregation. The effect of tyrphostin B46 was also time-dependent. The same concentration of these inhibitors produced very little or no inhibition of platelet-activating factor (PAF)-induced aggregation. The effects of tyrphostins B42 and B46 on thrombin- and PAF-stimulated PTP were generally similar, although some bands were more strongly inhibited when thrombin was the agonist. Therefore, although thrombin and PAF both act via G-protein coupled receptors, PAF may be capable of utilising an alternative signal transduction pathway to that used by thrombin.