DNA SYNTHESIS AND THYMIDINE KINASE ACTIVITY OF RAT COLON EPITHELIAL CELLS FRACTIONATED BY DISCONTINUOUS Ficoll gradient: Brief communication

Epithelial cells from colons of adult Sprague-Dawley rats were fractionated on a discontinuous Ficoll gradient at low centrifugal forces (170 x g) for approximately 60 minutes. Epithelial cells were separated into three distinct zones, whereas cell debris, yeast, and bacteria remained at the top of the gradient. The percentage of cells in each zone was inversely related to the density of the gradient. More than 95% of the cells were morphologically intact and viable (excluded trypan blue). Cells sedimenting at higher densities of Ficoll exhibited higher thymidine kinase activity and DNA synthesis, suggestive of active cell division. The cells sedimenting at lower densities of Ficoll showed the least thymidine kinase activity and DNA synthesis, properties that are compatible with those of mature absorptive cells. Tall columnar cells with vesicular nuclei were predominant in the fraction sedimenting at the lowest density (top fraction). At higher densities (middle and lower fractions), most of the cells were short and columnar with basally located condensed dark-staining nuclei.