Pyrimidine nucleoside metabolism in mammalian cells: An in vitro comparison of two rodent species

Abstract

The incorporation of thymidine into DNA has been studied in splenic and cultured cells of the golden hamster ( Mesocricetus auratus) and the goldenmantled ground squirrel ( Citellas lateralis). Considerably less uptake was observed in cells of the latter species. The reduced incorporation of thymidine found in cells of the ground squirrel is not due to a defective intracellular permeability, an inability to synthesize thymidine kinase or to trapping in an abnormally large nucleotide pool. It appears to derive from an unusually active catabolic pathway for thymidine and other pyrimidine nucleosides including deoxyuridine, uridine, deoxycytidine and cytidine. At critical concentrations the breakdown of nucleosides is sufficient to deplete the medium of these substances. Little, if any, difference is observed in the degradation of thymidine by liver slices from the same animals.