A contraction-mediating receptor for UTP, presumably P2Y2, in rat vas deferens

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Abstract
The possible existence of a contraction-mediating P2-receptor for uracil nucleotides was investigated in the rat vas deferens. In order to minimize breakdown of nucleotides, Evans blue was used as an inhibitor of ecto-nucleotidases. UTP was degraded by rat vas deferens tissue, and the degradation was inhibited by Evans blue (100 µM). In the absence of other drugs, UTP and UDP elicited marginal contractions. Evans blue (100 µM) greatly enhanced contractions elicited by the uracil nucleotides. When the medium contained α,β-MeATP (100 µM) in addition to Evans blue in order to desensitize contraction-mediating P2X1-receptors, responses to UTP and UDP were not changed; in contrast, responses to α,β-MeATP were virtually abolished and contractions elicited by ATP and ADP were greatly reduced; EC50 values were 122 µM for UTP and 58 µM for ATP under these conditions. The P2-receptor antagonist suramin attenuated contractions elicited by UTP (320 µM) and α,β-MeATP (32 µM) in the presence of Evans blue; pyridoxalphosphate-6-azophenyl-2',5'-disulphonate (iso-PPADS) also reduced responses to α,β-MeATP but, at up to 100 µM, did not alter contractions elicited by UTP. Incubation of vasa deferentia in nominally calcium-free medium almost abolished the response to α,β-MeATP (32 µM), while a major part of the contraction elicited by UTP (320 µM) was preserved. In the presence of Evans blue and α,β-MeATP, prior addition of UDP (3200 µM) or ATP (320 µM), without washout, markedly reduced the response to UTP (320 µM); UTP and ATP also reduced the response to UDP; in contrast, prior addition of UTP or UDP did not alter the contraction to ATP. The results demonstrate the existence of a contraction-mediating, uracil nucleotide-sensitive P2Y-receptor in rat vas deferens, distinct from the P2X1-receptor. Pharmacological analysis indicates that it is P2Y2.

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