Structural and biochemical aspects of liver cell nuclear organization in normal and scalded rats.

The response of rat liver nuclei to thermal injury was studied at the ultrastructural and biochemical levels using nuclei isolated in the presence of either Mg2+ or polyamines and metal chelators. The extent of chromatin condensation, as revealed by electron microscopy, increased in the order: nuclei in situ, Mg-stabilized nuclei, polyamine-stabilized nuclei. In addition, we observed that thermal injury caused an increase in the number of nuclear pores, an enlargement of nucleoli and an accumulation of ribonucleoprotein material. Along with this, greater amounts of protein, DNA and RNA were retained in nuclei from scalded rats. The salt-resistant residue from Mg-stabilized nuclei was a spherical proteinaceous structure of the nuclear matrix, whereas that of the polyamine-stabilized nuclei was amorphous and deprived of three major constituents of the spherical matrix, the 60-70 X 10(3) Mr lamina proteins. However, exposure of the polyamine-stabilized nuclei to Ca2+ and Mg2+ rendered the 60-70 X 10(3) Mr proteins salt-insoluble and thus enabled the extraction of a spherical residual nuclear structure. This structure was highly enriched in DNA, RNA and non-histone proteins and, hence, more like dehistonized nuclei than the minimal residual nuclear structure. It retained 70% of DNA in the controls but virtually all the DNA in scalded rats. This difference was interpreted to reflect activation-related changes in chromatin organization.