Inhibition of 5'-chloro-5'-deoxyadenosine on phosphoinositide and protein phosphorylation in swine platelets

To study the effects of adenosine on the phosphorylation of phosphoinositides and proteins in platelets.

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.

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].

Adenosine affects the phosphoinositide signaling pathway in platelets, which helps to clarify the inhibition of adenosine on platelet activation.