Uptake of tritiated phosphatidylcholine by isolated rat liver nuclei studied by electron microscope autoradiography in albumin embedded specimens.

The transfer of phosphatidylcholine from multilamellar vesicles to isolated rat liver nuclei was studied by means of electron microscope autoradiography. To avoid the possible loss or the artifactual redistribution of the phospholipid occurring during dehydration with organic solvents and plastic embedding, the fixed specimens were embedded in aqueous albumin, which was then hardened by glutaraldehyde and dehydrated physically. The quantitative analyses of the autoradiograms demonstrated that part of the labelled phosphatidylcholine was taken up by the isolated nuclei and was transferred inside the nucleoplasm. The uptake corresponded to the loss of the vesicular arrangement, probably owing to the formation of a lipoprotein complex with the nuclear proteins. The results provide evidence that the lipid-induced changes of transcriptional activity occur upon the actual interaction of the exogenous phospholipid with the inner nuclear components.