Is adenosine a second metabolic substrate for human red blood cells?
Adenosine is present in the micromolar range in human plasma. In this study, metabolism of adenosine, which was maintained between 0.62 +/- 0.03 and 2.92 +/- 0.43 microM by means of a continuous infusion using a Harvard infusion pump, was investigated in human red blood cells. It was found that lactate production increases linearly as the adenosine concentration was raised. Cells infused with an average adenosine concentration of 2 microM produced lactate comparable to that produced by 5 mM glucose. The extent to which ATP concentration is maintained by adenosine also depends on its concentration. After a 4 h infusion with an average adenosine concentration of 0.7 microM, ATP content amounts to 75% of the glucose control. Raising the adenosine infusion concentration to 1.5 microM results in a full maintenance of ATP levels and at concentrations higher than 1.5 microM, adenosine produces a net synthesis of ATP. A net synthesis of ATP also occurs with adenosine concentration below 1.5 mi
