An electron spin resonance study of the novel radical cation produced during the horseradish peroxidase-catalyzed oxidation of tetramethylhydrazine

Thrombin stimulation of [³²P]-prelabeled platelets induces a rapid decrease of the radioactivity from phosphatidylinositol-4,5-bisphosphate. No significant change is observed in phosphatidylinositol-4-monophosphate. The initial, thrombin-induced decrease of phosphatidylinositol-4,5-bisphosphate is not inhibited by cytochalasin D or by compounds that interfere with the mobilization of Ca²⁺ such as 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, the calmodulin-antagonist, trifluoperazine, prostacyclin and cyclic AMP. Our information indicates that the rapid loss of phosphatidylinositol-4,5-bisphosphate is linked to receptor activation and insensitive to Ca²⁺-mobilization.