Evidence for the formation of inositol 4‐monophosphate in stimulated human platelets

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Abstract
Human platelets were prelabeled with [3H]inositol and exposed to thrombin or vasopressin. The radioactive inositol monophosphates were separated by high‐performance liquid chromatography and identified by cochromatography with unlabeled standard substances. Radioactive inositol 1‐monophosphate (Ins 1‐P) and inositol 4‐monophosphate (Ins 4‐P) were detected in unstimulated platelets and accumulated in response to thrombin or vasopressin. Ins 4‐P as well as Ins 1‐P increased after the formation of inositol 1,4‐bisphosphate (Ins 1,4‐P,) and inositol 1,4,5‐trisphosphate (Ins 1,4,5‐P3). Lithium augmented the accumulation of Ins 1‐P and Ins 1,4‐P2 in stimulated platelets, and also of Ins 4‐P in platelets stimulated by vasopressin, but not by thrombin. The results indicate that Ins 1,4‐P2 formed in stimulated platelets is partly degraded to Ins 4‐P. The significance of Ins 4‐P as a marker molecule for the study of inositol phosphate metabolism in stimulated cells is discussed.