Intracellular adenosine in isolated rat liver cells.

Our objective was to determine whether a non-extracellular pool of adenosine exists in mammalian cells. Rat liver cells were dispersed by a collagenase perfusion technique and suspended in buffered salt solution. The adenosine content of these suspensions rose during hypoxia. Exogenous adenosine deaminase prevented or reversed the hypoxic increment but failed to reduce suspension adenosine levels to zero. This residual adenosine pool (average size = 85 +/- 10 pmol/mg protein) was not located in the extracellular medium, on surface adenosine receptors or in solution in the cytoplasm. A likely locus is the adenine-analog binding protein which has been described for liver and other tissues. Thus, our study supports the existence of an intracellular adenosine pool in isolated rat liver cells which is a large fraction of the total tissue adenosine. This situation may exist in other cell types as well, based on the ubiquity of the adenosine binding protein. Tissue adenosine content may not, therefore, accurately reflect interstitial adenosine concentration; thus, such measurements must be interpreted cautiously. It is not clear what, if any, functional role this putative, intracellular, bound adenosine pool plays in local vasoregulation.