Characterization of P-1,P-4-diadenosine 5 '-tetraphosphate binding on bovine aortic endothelial cells

In recent years it has become increasingly clear that alpha,omega-dinucleot ides act as extracellular modulators of various biological processes. p(1), P-4-diadenosine 5'-tetraphosphate (Ap,A) is the best characterized alpha,om ega-dinucleotides and acts as an extracellular signal molecule by inducing the release of nitric oxide (NO) from bovine aortic endothelial cells (BAEC ) (R. H. Hilderman, and E. F. Christensen (1998) FEBS Lett. 407, 320-324). However, the characteristics of Ap(4)A binding to endothelial cells have no t been determined. In this report we demonstrate that Ap(4)A binds to a het erogeneous population of receptors on BAEC. Competition ligand-binding stud ies using various adenosine dinucleotides, guanosine dinucleotides, adenosi ne/guanosine dinueleotides, and synthetic P-2, purinoceptor agonists and an tagonists demonstrate that Ap(4)A binds to a receptor on BAEC that has a hi gh affinity for some of the adenosine dinucleotides. The apparent IC50 valu es for Ap(4)A, Ap(2)A, and Ap(3)A are between 12 and 15 mu M, while the app arent IC50 values for Ap(5)A and Ap(6)A are greater than 500 mu M. Evidence is also presented which suggests that this receptor can be classified as a putative P-4 purinoceptor. Competition studies also demonstrate that Ap(4) A binds at a lower affinity to a second class of binding sites, (C) 1999 Ac ademic Press.