The critical role of adenosine and guanosine in the affinity of dinucleoside polyphosphates to P(2X)-receptors in the isolated perfused rat kidney.

1. The activation of P(2x)-receptors in the rat renal vasculature by dinucleoside polyphosphates with variable phosphate group chain length (Xp(n)X; X=Adenin (A) /Guanin (G), n=4 - 6) was studied by measuring their effects on perfusion pressure of the isolated perfused rat kidney at constant flow in an open circuit. 2. Like Ap(4)A, Ap(5)A and Ap(6)A the dinucleoside polyphosphates Ap(4)G, Ap(5)G and Ap(6)G exerted a vasoconstriction which could be blocked by suramin and pyridoxal-phosphate-6-azophenyl-2; 4-disulphonic acid (PPADS). 3. Gp(4)G, Gp(5)G and Gp(6)G showed only very weak vasoconstriction at high doses. 4. Ap(6)A and alpha, beta-meATP could not be blocked by the selective P(2x1)-receptor antagonisten NF023 (30 microM), whereas Ap(4)A, Ap(4)G, Ap(5)A, Ap(5)G and Ap(6)G were partially blocked by NF023. 5. Inhibition of endothelial NO-synthase by N(omega)-nitro-L-arginine methyl ester (L-NAME) did not affect vasoconstrictions induced by dinucleosidepolyphosphates. 6. P(2x)-receptor can only be activated if at least one adenosine moiety is present in the molecule. 7. Ap(n)G show a weaker vasoconstrictive action than corresponding Ap(n)A, concluding that two adenosine moieties enhance the P(2x)-receptor binding and activation. 8. Xp(n)X containing five phosphate groups show the most pronounced vasoconstrictive effect whereas four phosphate groups show the less effect, therefore the number of phosphate groups critically changes receptor affinity. 9. Additional experiments using permanent perfusion with alpha, beta-methylene ATP (alpha,beta-meATP) and the selective P(2x1)-receptor antagonist NF023 showed that the newly discovered human dinucleoside polyphosphates activated the vascular P(2x1)-receptor and an recently identified new P(2x)-receptor subtype. 10. The differential effects of dinucleoside polyphosphates allow a fine tuning of local perfusion via composition of Xp(n)Xs.