Pharmacological characterization of nucleotide P2Y receptors on endothelial cells of the mouse aorta

1 Nucleotides regulate various effects including vascular tone. This study was aimed to characterize P2Y receptors on endothelial cells of the aorta of C57BL6 mice. Five adjacent segments ( width 2 mm) of the thoracic aorta were mounted in organ baths to measure isometric force development. 2 Nucleotides evoked complete ( adenosine 50 triphosphate ( ATP), uridine 50 triphosphate ( UTP), uridine 50 diphosphate ( UDP); > 90%) or partial ( adenosine 50 diphosphate ( ADP)) relaxation of phenylephrine precontracted thoracic aortic rings of C57BL6 mice. Relaxation was abolished by removal of the endothelium and was strongly suppressed ( 490%) by inhibitors of nitric oxide synthesis. 3 The rank order of potency was: UDP similar to UTP similar to ADP > adenosine 5'-[gamma-thio] triphosphate ( ATP gamma S) > ATP, with respective pD(2) values of 6.31, 6.24, 6.22, 5.82 and 5.40. These results are compatible with the presence of P2Y(1) ( ADP4ATP), P2Y(2) or P2Y(4) ( ATP and UTP) and P2Y6 ( UDP) receptors. 4 P2Y4 receptors were not involved, since P2Y4- deficient mice displayed unaltered responses to ATP and UTP. 5 The purinergic receptor antagonist suramin exerted surmountable antagonism for all agonists. Its apparent pK(b) for ATP ( 4.53 +/- 70.07) was compatible with literature, but the pKb for UTP ( 5.19 +/- 0.03) was significantly higher. This discrepancy suggests that UTP activates supplementary non-P2Y2 receptor subtype(s). 6 Further, pyridoxal-phosphate-6-azophenyl-20-40-disulphonic acid ( PPADS) showed surmountable ( UTP, UDP), nonsurmountable ( ADP) or no antagonism ( ATP). 7 Finally, 20-deoxy-N-6-methyladenosine3',5'- bisphosphate ( MRS2179) inhibited ADP-evoked relaxation only. 8 Taken together, these results point to the presence of functional P2Y1 ( ADP), P2Y2 ( ATP, UTP) and P2Y6 ( UDP) receptors on murine aorta endothelial cells. The identity of the receptor( s) mediating the action of UTP is not fully clear and other P2Y subtypes might be involved in UTP-evoked vasodilatation.