Involvement of multiple receptors in the actions of extracellular ATP: the example of vascular endothelial cells

Abstract

The role of ATP and ADP as intercellular mediators is now well established. The presence of the nucleotides in extracellular fluids can result from several mechanisms: cell lysis, selective permeabilization of the plasma membrane and exocytosis of secretory vesicles, such as platelet dense bodies. Extracellular adenine nucleotides are rapidly degraded by ectonucleotidases expressed inter alia on the surface of endothelial cells. They act on cells via the family of P 2 receptors which encompasses more than 5 subtypes, some of which have been cloned recently. The P 2T, P 2U and P 2Y receptors belong to the superfamily of receptors coupled to G proteins, whereas the P 2X receptor is a cation channel and the P 2Z receptor a non-selective pore. ATP and ADP stimulate the endothelial production of prostacyclin (PGI 2) and nitric oxide (NO), two vasodilators and inhibitors of platelet aggregation, via an increase in cytosolic Ca 2+. This action of adenine nucleotides is believed to limit the extent of intravascular platelet aggregation and to help localize thrombus formation to areas of endothelial damage. The endothelial response to nucleotides is mediated by at least two distinct subtypes of P 2 receptors, P 2Y and P 2U, both coupled to phospholipase C.