The effects of adenosine and inosine on Rana ridibunda erythrocyte metabolism were studied. Adenosine can be metabolized by Rana ridibunda erythrocytes as a carbon source for glycolysis to maintain ATP levels, whereas neither inosine nor glucose could maintain ATP levels. The rate of lactate production was maximal (2.89 mumol ml-1 red cell h-1) in the presence of adenosine together with glucose compared with that in the presence of glucose or adenosine alone. Inosine sustained a similar rate of

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... lactate production as did glucose. The concentrations of phosphorylated hexoses increased during 4 h of incubation in the presence of adenosine either with or without glucose. The presence of sodium iodoacetate accelerated the loss of ATP; furthermore, levels of lactate and pyruvate were significantly reduced in the presence of either adenosine or inosine. Ouabain strongly inhibited ATP and lactate formation in the presence of adenosine, whereas the levels of ATP and lactate were almost unchanged in the presence of inosine. An inhibitor of adenosine transport, dipyridamole, impeded the increases in erythrocyte lactate and ATP concentration in the presence of adenosine but did not modify the effects of inosine.