The stable pyrimidines UDPβS and UTPγS discriminate between contractile cerebrovascular P2 receptors

Abstract

Extracellular nucleotides were used to characterise the contractile P2 receptors in the rat basilar artery. The isometric tension was recorded in vitro and receptor mRNA expression was examined by reverse transcriptase polymerase chain reaction (RT-PCR) after endothelium-denudation. Transient vasoconstriction was evoked by αβ-methylene-adenosine triphosphate (αβ-MeATP), indicating the presence of P2X 1 receptors. The P2Y receptors were analysed after P2X receptor desensitisation with 10 μM αβ-MeATP. Uridine diphosphate (UDP) and uridine triphosphate (UTP) induced sustained contractions of similar magnitude. The stable nucleotide analogue, uridine 5′- O-thiodiphosphate (UDPβS), was clearly more potent than uridine 5′- O-3-thiotriphosphate (UTPγS), suggesting prominent contractile effects of P2Y 6 receptors. P2Y 2 and P2Y 4 receptors might also be involved in nucleotide responses, since UTPγS and adenosine 5′- O-3-thiotriphosphate (ATPγS) were of similar potency. The P2Y 1 selective agonists, adenosine 5′- O-thiodiphosphate (ADPβS) and 2-methylthioadenosine diphosphate (2-MeSADP) did not induce contractions. RT-PCR analysis demonstrated P2X 1, P2Y 1, P2Y 2 and P2Y 6 receptor mRNA expression, while the P2Y 4 band was weak. In conclusion, extracellular nucleotides induce contractions of cerebral arteries primarily by activation of P2Y 6 receptors on smooth muscle cells, with a lesser contribution of P2Y 2 and P2X 1 receptors. Although mRNA for the P2Y 1 receptor was detected by RT-PCR, it does not mediate contraction.