The presence of G1 and G2 populations in normal epithelium of rat urinary bladder.

The cell population kinetics of transitional epithelium of the rat urinary bladder was analysed by (3H) thymidine autoradiography and pararosanilin Feulgen DNA cytofluorometry. By flash and 72 h continuous DNA labelling, the generative cells of the transitional epithelium were found to be well localized in the basal layer, and it was postulated that che cells produced by cell proliferation in the basal layer would migrate towards the surface, maintaining direct attachment to the basement membrane by anchorage of a cellular process. Analyses of normal and wounded transitional epithelium revealed that 58.8% of all basal cells are G0 cells in G1 phase (G1-population), and 59.0% of the remaining basal cells reside in prolonged (75.1-108.0 h) G2 phase, preserving the ability to divide (G2-population). The cell cycle time of the generative basal cells including the long G2 phase was calculated as 129.1-162 h. All the cells existing in upper layers were found to be also G0 cells in G1 phase, with the DNA amounts of 2C class. No polyploid cells could be detected except for 2C-2C binucleated cells in the superficial layer. The existence of a G2-population may serve for the urgent need of cell incrementation to repair cell loss as the cells in G2 phase can divide without the time-delay needed for DNA synthesis. The rat transitional epithelium, which is composed exclusively of proliferating and potentially proliferative cells, will have much greater capability to repair damage than stratified squamous epithelia.