Turnover of P32 in Different Types of Nuclei from Rabbit Liver. ∗

Abstract

Hitherto investigations into nuclear metabolism have been carried out with mixtures of nuclei isolated from the various cells which make up the tissue being studied. By differential centrifugation it has been possible to separate nuclei isolated from rabbit liver into two fractions, one made up predominantly of hepatic cell nuclei, the other containing nuclei of other types of cells present in the liver and to compare P³²-turnover in hepatic cell nuclei with other types of nuclei found in the liver.

Nuclei were isolated in 5% citric acid as previously described ( 1 ). They were then subjected to centrifugation at 900 g for 3 minutes, after which successive layers were removed with a pipette and examined microscopically. The nuclei of the upper layers were predominantly spherical, while those near the bottom of the centrifuge tube were predominantly ellipsoidal, fusiform and cylindrical, together with occasional ones which were constricted and lobed. By repeated centrifugation (5x) of the upper and lower layers, about half of the nuclei could be separated into the two groups mentioned above (Fig. 1 and 2). In each group counts were made of the frequency of the spherical and non-spherical types. In Group 1, 90-95% of the nuclei were spherical, while in group 2, 98-99% were non-spherical. On the basis of morphology, the predominant type of nucleus in Group 1 could readily be identified as that of the hepatic cell. Those of Group 2, could be recognized as fibroblast. Reticulo-endothelial, endothelial and polymorpholeucocyte nuclei.

Figure

P³² was administered intravenously to rabbits as Na₂HP0₄, and 3 hours later the livers were perfused and the nuclei isolated and separated as described above. Total phosphorus and radioactive phosphorus were determined in aliquots of each group.