P2 purinoceptors on vascular endothelial cells: physiological significance and transduction mechanisms.

The characterization of P2 gamma purinoceptors on vascular endothelial cells has progressed rapidly since their existence was first demonstrated in 1983. They transduce the actions of extracellular ATP and ADP--endothelium-dependent relaxation, prostacyclin synthesis, endothelial cell mitogenesis--which play a vital role in the interaction between platelets (a rich source of extracellular adenine nucleotides) and the vessel wall. Release of prostacyclin limits the extent of intravascular platelet aggregation following vascular damage and platelet stimulation, while the mitogenic effect may accelerate the repair of a lesion. P2 gamma receptors on endothelial cells are coupled to a phospholipase C by a GTP-binding protein. Jean-Marie Boeynaems and Jeremy Pearson explain how the increases in cytoplasmic Ca2+ and diacylglycerol resulting from this initial event mediate several further effects. In particular, activation of a Ca2(+)-sensitive phospholipase A2 explains the increased synthesis of prostacyclin, while the phosphorylation of several proteins by calmodulin-dependent kinases modulates other endothelial cell functions.