Effect of adenosine receptor agonists on release of the nucleoside analogue [3H]formycin B from cultured smooth muscle DDT1 MF-2 cells

Adenosine has receptor-mediated effects in a variety of cell types and is predominantly formed from ATP by a series of nucleotidase reactions. Adenosine formed intracellularly can be released by bidirectional nucleoside transport processes to activate cell surface receptors. We examined whether stimulation of adenosine receptors has a regulatory effect on transporter-mediated nucleoside release. DDT1 MF-2 smooth muscle cells, which possess nitrobenzylthioinosine-sensitive (ES) transporters as well as both adenosine A(1) and A(2) receptors, were loaded with the metabolically stable nucleoside analogue [H-3]formycin B. N-6-cyclohexyladenosine (CHA), a selective adenosine A(1) receptor agonist, produced a concentration-dependent inhibition of [H-3]formycin B release with an IC50 value of 2.7 mu M. Further investigation revealed CHA interacts directly with nucleoside transporters with a K-i value of 3.3 mu M. Neither 5'-N-ethylcarboxamidoadenosine (NECA), a mixed adenosine A(1) and A(2) receptor agonist, nor CGS 21680, a selective adenosine A(2A) receptor agonist, affected nucleoside release. We conclude that release of the nucleoside formycin B from DDT1 MF-2 cells is not regulated by adenosine A(1) or A(2) receptor activation. (C) 1998 Elsevier Science B.V.