Separation of intact rat hepatocytes and rat liver nuclei into ploidy classes by velocity sedimentation at unit gravity.

A system is described which permits the separation of isolated hepatocytes and isolated rat liver nuclei belonging to different ploidy classes by velocity sedimentation at unit gravity. The problem of obtaining single cells suspensions is discussed and preparations were obtained that contained 96% single hepatocytes. By improving the sedimentation method, it took 2.5 h to separate rat liver nuclei on sucrose gradients into diploid and tetraploid ploidy classes. Recoveries were generally over 95%. The diploid band was 99% pure. DNA and protein content of the ploidy classes were measured. After partial hepatectomy and [3H]thymidine injection it was found that the label moved largely into the tetraploid compartment. Isolated hepatocytes were fractionated in 1 h on Ficoll gradients. Erythrocytes were separated from small nucleated cells and the population of hepatocytes was clearly separated from these two cell populations. Diploid hepatocytes were 80% and tetraploid hepatocytes were 99% pure. Viability was about 80% after fractionation. The gene dosage of NADPH cytochrome c reductase, succinate dehydrogenase and lactate dehydrogenase was estimated in diploid and tetraploid hepatocytes. Gene dosage was equal in diploid and tetraploid hepatocytes for succinate dehydrogenase and NADPH cytochrome c reductase. It is suggested, after correcting for non-viable tetraploid hepatocytes, that the gene dosage of lactate dehydrogenase was significantly lower in diploid than in tetraploid hepatocytes.