Compartmentalization of uridine and uridine 5'-monophosphate in rat liver slices.

The metabolism of exogenous uridine, uridine 5’-monophosphate, and uracil by rat liver slices was studied using in vitro superfusion systems. Mixtures of 3Hand 14Clabeled uridine, uridine 5’-monophosphate, uracil, and erotic acid were superfused at a constant rate until an isotopic steady state was achieved. Isotopic ratios and concentrations of labeled pyrimidines were measured in tissue and perfusate. The results of these experiments indicated marked compartmentalization in the intracellular distribution of uridine 5’-monophosphate, uridine, and uracil. On the basis of a model justified by the experimental findings, rates of metabolism of exogenous pyrimidines in the plasma membrane and rates of passage of these compounds through the membranes were estimated.