ADENOSINE 5'-TRIPHOSPHATE IS THE PREDOMINANT SOURCE OF PERIPHERAL ADENOSINE IN HUMAN B LYMPHOBLASTS

Adenosine 5'-triphosphate (ATP) and adenosine are the crucial endogenous signaling molecules in immunity and inflammation. In this study we identified the source of extracellular adenosine in human B lymphoblasts, and evaluate the ATP release and metabolism. We observed that the B cells continuously released substantial quantities of ATP (35 pmo1/106 cells) when subjected to slow motion in the incubation medium. The adenosine level in the B cell incubation medium was very low, and increased (5-fold) upon inhibition of adenosine deaminase activity with 10 itM of 2deoxycoformycin (DCF). Inclusion of an inhibitor of equilibrate nucleoside transport (nitrobenzylthioinosine) in the incubation medium in the presence of DCF resulted in the elevation of adenosine level by 9-fold. Inhibition of ectoATPase activity with 100 pM of ARL67156 was associated with a 2-fold increase of the extracellular ATP level and a 3-fold decrease of adenosine concentration in the cell culture media. Inclusion of a,3-methyleneadenosine 5'diphosphate, a selective inhibitor of ecto-5'-nucleotidase in the incubation medium resulted in a significant decrease (7fold) the adenosine concentration. In conclusion, our results indicate that ATP released from the B cell is the primary source of peripheral adenosine, and that the activities of ecto enzymes and the efficiency of Ado uptake through the nucleoside transporters determine the Ado level on the B cell surface.