Phosphoinositide metabolism in resting and thrombin‐stimulated human platelets Evidence against metabolic heterogeneity

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Abstract
The specific radioactivity of the phosphodiester and phosphomonoester moieties of the phosphoinositides was determined in resting and thrombin‐stimulated platelets that were prelabelled with [32P] Pi. In the unstimulated cells, the specific radioactivity of the monoester phosphates of PIP and PIP2 was similar. Both prolonged incubation at 37°C and upon stimulation with 0.5 U/ml of thrombin, the specific radioactivity of the monoester phosphates decreased 10–15% in both polyphosphoinositides. In the unstimulated cells, the specific radioactivity of the diester phosphates was similar in PI, PIP and PIP2 but amounted only to 3% of the activity of the monoester groups. Prolonged incubation of the unstimulated cells as well as stimulation with thrombin induced a similar 5–6 fold increase in specific radioactivity of the diester phosphate of PI, PIP and PIP2. The results indicate that the phosphoinositides in both resting and thrombin‐stimulated platelets exist in a metabolically homogeneous pool.

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