The Effect of the Intracellular Calcium Chelator Quin-2 on the Platelet Phosphoinositide Metabolism, Protein Phosphorylation and Morphology

Summary

When human platelets prelabeled with [³²P] orthophosphate were loaded with Quin-2, the ³²P-incorporation in phosphatidic acid, phosphatidylinositol-4 phosphate and phosphatidylinositol-4,5 bisphosphate increased, that in phosphatidylinositol decreased. These effects occurred in a Quin-2-concentration- dependent manner. On stimulation of the serotonin-S₂ receptor, signal transduction, measured as changes in labeling in phospholipids and phosphoproteins, was altered in the presence of the fluorophore. Microscopic evaluation illustrated that Quin-2 affected platelet morphology as well in resting as in stimulated platelets. A correlation between platelet shape change and myosin light chain phosphorylation was apparent.

The data evidence that the Quin-2 that is widely used for fluorometric determination of intracellular Ca²⁺, affects the metabolism of inositol-containing phospholipids whose breakdown is a key event in Ca²ⁱ⁺-mobilization on excitatory platelet activation. These fluorophore-induced alterations might, besides the Ca²-chelating properties, play an important role in the Ca²⁺ dependent signalling processes in these cells.

Keywords

Human platelets - Quin-2 - Serotonin - Signal transduction - Morphology

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