Characterization of vascular P2 purinoceptors in the rat isolated perfused kidney

Abstract In isolated, constant-pressure perfused rat kidneys at basal vascular tone, injected P 2 purinoceptor agonists evoked vasoconstriction (α,β-methylene ATP > β,γ-methylene ATP > ATP-γ-S > 2-methylthio ATP > ATP > ADP = UTP). In kidneys with raised tone, the nucleotides produced vasodilatation at low doses (2-methylthio ATP > ADP = ATP = ATP-γ-S > UTP; α,β-methylene ATP and β,γ-methylene ATP, inactive), and constriction at high doses (α,β-methylene ATP > β,γ-methylene ATP > ATP-γ-S > 2-methylthio ATP > ADP = ATP > UTP). Removal of the endothelium abolished the dilator responses to the agonists. N G -Nitro- l -arginine methylester ( l -NAME, 5 × 10 −5 M) abolished vasorelaxation in response to 2-methylthio ATP, a response which could be restored by additional l -arginine (3 × 10 −3 M). Both vasodilation and constriction due to the nucleotides remained unaffected by indomethacin (3 × 10 −6 M), S -( p -nitrobenzyl)-6-thioinosine (3 × 10 −5 M) and 8-phenyltheophylline (3 × 10 −6 M). Pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS, 1–3 × 10 −6 M), inhibited vasoconstriction caused by α,β-methylene ATP, 2-methylthio ATP and UTP, but not by ATP. Suramin (3 × 10 −5 M) caused a rightward shift of the dose-response curves for constriction caused by α,β-methylene ATP (27-fold) and 2-methylthio ATP (5-fold), whereas the ATP curve was shifted to the left (20-fold). With Evans blue (10 −5 M), vasodilatation due to the nucleotides was abolished and the dose-response curves for vasoconstriction caused by ATP and UTP were shifted left more than 100-fold, the effect to both could not be antagonized by PPADS (3 × 10 −6 M). These results suggest: (1) the different rank orders of P 2 purinoceptor agonist potencies for constrictor and dilator responses in perfused rat kidney are consistent with mediation via P 2X and P 2Y purinoceptors, respectively; (2) P 2X purinoceptors, selectively sensitive to blockade by PPADS, are located on vascular smooth muscle; (3) endothelial P 2Y purinoceptor stimulation results in vasodilatation involving NO synthesis but not release of prostanoids; (4) Evans blue, which appears to combine selective P 2Y purinoceptor blockade and strong inhibition of ecto-nucleotidases, potentiates vasoconstriction in response to the degradable nucleotides, ATP, 2-methylthio ATP and UTP; (5) additionally, Evans blue unmasks a PPADS-insensitive P 2U purinoceptor where the nearly equipotent nucleotides, ATP and UTP, can produce vasoconstriction.