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Aim: To study the effects of adenosine on the phosphorylation of phosphoinositides and proteins in platelets., Methods: In the presence of Mg2+ and/or Ca2+, swine thrombocytic membranes were incubated with [gamma-32P]ATP at 30 degrees C for 3 min and the incorporations of 32P into phospholipids or proteins were measured., Results: 5'-Chloro-5'-deoxyadenosine decreased the formation of phosphatidylinositol 4-phosphate and phosphatidylinositol 4, 5-bisphosphate [IC50 71 and 75 (95% confidence limits 60-85 and 62-90) mumol.L-1, respectively], behaving as a competitive inhibitor to ATP, and inhibited the phosphorylation of pleckstrin (the major protein kinase C substrate) and myosin light chain [IC50 75 and 82 (95% confidence limits 62-90 and 66-102) mumol.L-1, respectively]., Conclusion: Adenosine affects the phosphoinositide signaling pathway in platelets, which helps to clarify the inhibition of adenosine on platelet activation.

In the presence of Mg2+ and exogenous phosphatidylinositol-4-phosphate, swine thrombocytic membranes were incubated with [gamma-32P]ATP at 30 degrees C for 3 min and the incorporations of 32P into phospholipids and proteins were measured. Spermine stimulated the formation of phosphatidylinositol-4,5-bisphosphate (optimal concentration 0.25 mmol.L-1) and inhibited the phosphorylation of 47 K protein (IC50 1 mmol.L-1). This helps to clarify the effect of spermine on cell growth and proliferation.