Properties of Na+/K+ ATPase and alkaline phosphatase alter during spontaneous and radiation-induced leukemogenesis in mice

We characterized properties of Na+/K+ ATPase and alkaline phosphatase in thymocytes or thymoblasts from mice of two strains: AKR, in which thymoma developed spontaneously and C57Bl, in which the development was induced by X-irradiation (total dose: 5.4 Gy in 3 fractions). We found that before thymoma could be discerned morphologically--properties of the two enzymes altered. There was a decrease in 86Rb uptake and in the rate of ATP hydrolysis per cell (both strains) as well as an increase in alkaline phosphatase activity per cell (C57Bl mice). In both spontaneous and radiation-induced thymomas 86Rb uptake, ATP hydrolysis and 3H-ouabain binding per cell were higher than in normal thymuses. Likewise, alkaline phosphatase activity per cell was higher in thymomas than in thymuses; this increase was accompanied by the appearance of additional isoenzyme(s) (1 in AKR, 2 in C57Bl). These changes were compared with cAMP content and 3H-thymidine incorporation, taken as indicators of the proliferative activity, and their high correlation in both AKR and C57Bl mice allowed to distinguish a pre-leukemic period. In that period thymoblasts clearly differed from the normal ones in Na+/K+ ATPase and alkaline phosphatase properties, as well as proliferation, although the morphology of the thymus was still unchanged.