α, β-MeATP augments the UTP contraction of rabbit basilar artery

Abstract The mechanism underlying the interaction between α,β-methyleneadenosine 5′-triphosphate (α,β-MeATP) and uridine 5′-triphosphate (UTP) was investigated using the basilar artery of a rabbit. UTP induced a concentration-dependent contraction, whereas P2X receptor agonists, such as α,β-MeATP and 2-methylthioadenosine 5′-triphosphate (2-MeSATP), did not induce any contraction up to 100 μM. α,β-MeATP augmented the UTP contraction two-fold, immediately and reversibly. This effect was observed with ectonucleotidase inhibition with 1 mM Ni 2+ , the removal of extracellular Ca 2+ or Evans blue. The contractile response to adenosine 5′- O -(3-triphosphate) (ATPγS), a selective agonist for P2Y 4 , was augmented by pretreatment with α,β-MeATP also. ATPγS had no additional effect on the UTP contraction fully activated with α,β-MeATP. UTP (100 μM) did not induce an increase in cytosolic Ca 2+ in a rabbit basilar arterial strip; however, in the presence of 1 mM α,β-MeATP, UTP induced a significant increase in cytosolic Ca 2+ . These results suggest that α,β-MeATP facilitates the activation by UTP of the P2Y receptor (P2Y 4 ) of the rabbit basilar artery through mechanisms other than nucleotidase inhibition, and that it does not do so via a P2X receptor.