Mass Contents of Inositol 1,4,5-Trisphosphate and 1,2-Diacylglycerol in Human Platelets Stimulated with a Thromboxane Analogue and Thrombin

Summary

Mass contents of inositol 1,4,5-trisphosphate (IP₃) and 1,2-diacylglycerol (DG) were measured in U46619-stimulated human platelets. 1 µM of U46619 induced maximum responses in aggregation, 5-hydroxytryptamine (5HT) secretion and increase in intracellular free Ca²⁺ concentration ([Ca²⁺]_i). Aggregation was almost comparable to that induced by maximal dose (1 U/ml) of thrombin, while 5HT release was almost half. The initial [Ca²⁺]_i peak in response to U46619 was about half of thrombin stimulation. Production of IP₃ and DG was, however, less than one tenth of that seen in thrombin stimulation. The profile (time course and concentration-dependency) of IP₃ formation did not correlate with that of [Ca²⁺]_i, suggesting that U46619 stimulates IPs-dependent and -independent Ca²⁺ mobilization. DG production was small but sustained for more than 5 min. These findings support the recent hypothesis that aggregation is regulated by a delayed accumulation of DG. The low level of 5HT secretion could be explained by the low production of second messengers, IP₃ and DG.

• References

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