SELECTIVITY AND ACTIVITY OF ADENINE DINUCLEOTIDES AT RECOMBINANT P2X(2) AND P2Y(1) PURINOCEPTORS

1 Adenine dinucleotides (Ap(x)A, x=2-6) are naturally-occurring polyph osphated nucleotidic substances which are found in the CNS and are kno wn to be released in a calcium-dependent manner from storage vesicles in brain synaptosomes. The selectivity and activity of adenine dinucle otides for neuronally-derived recombinant P-2 purinoceptors were studi ed using P2x(2) and P2Y(1) subtypes expressed in Xenopus oocytes. 2 Fo r the P2Y(1) subtype derived from chick brain, Ap(3)A was equipotent a nd as active as ATP (EC(50) values: 375+/-86 nM and 334+/-25 nM, respe ctively). Ap4A was a weak partial agonist and other dinucleotides were inactive as agonists, None of the inactive dinucleotides were antagon ists nor modulated the acitivity of Ap(3)A and ATP. 3 For the P2X(2) s ubtype derived from rat PCl2 cells, Ap(4)A was as active as ATP but le ss potent (EC(50) values: 15.2+/-1 mu M and 3.7+/-0.7 mu M, respective ly). Other adenosine dinucleotides were inactive as either agonists or antagonists. 4 Ap(5)A (1-100 nM) potentiated ATP-responses at the P2x (2) subtype, showing an EC(50) of 2.95+/-0.7 nM for this modulatory ef fect. Ap(5)A (10 nM) shifted the concentration-response curves for ATP to the left by one-half log(10) unit but did not alter the Hill co-ef ficient for ATP (n(H)=2.1+/-0.1). Ap(5)A (10 nM) failed to potentiate Ap(4)A-responses but did enhance the efficacy of the Pt purinoceptor a ntagonist, suramin, by 12 fold at the P2x(2) subtype. 5 In conclusion, the results show that ionotropic (P2x(2)) and metabotropic (P2Y(1)) A TP receptors which occur in the CNS are activated selectively by natur ally-occurring adenine dinucleotides which are known to be released wi th nucleotides from storage vesicles. The observed potentiation of P2x (2)-responses by Ap(5)A, where co-released with ATP by brain synaptoso mes, may have a functional bearing in purinergic signalling in the CNS .