Newly evidenced pyrimidinoceptors and the P2x purinoceptors are present on the vascular smooth muscle and respectively mediate the UTP- and ATP-induced contractions of the dog maxillary internal vein

Abstract

P2 purinergic receptors and pyrimidinoceptors were studied by comparing the contractile responses to UTP with those to ATP, in the dog internal maxillary vein (IMV) after endothelium removal. The contraction curves were very different: rapid subsidence with ATP and sustained contraction with UTP. alpha beta methylene ATP induced desensitization to ATP, whereas it did not antagonize the UTP-induced contractions. Reactive blue 2 (RB2) was incapable of antagonizing contractions to ATP and UTP in this vessel. We showed that Nicardipine, a calcium antagonist, was more potent on the UTP-induced than on the ATP-induced contractions. The fact that RB2 did not potentialize the UTP-induced contractions, unlike what has been observed in the dog saphenous vein, suggests that a new category of pyrimidinoceptors have been evidenced on the IMV. Our results also indicate that ATP induces contraction via P2x rather than P2y purinoceptors. The receptors described here are localized on the vascular smooth muscle.