GRAIN COUNT THRESHOLD DEPENDENCE OF FLM CURVE PATTERN AND CELL CYCLE PARAMETERS OF HEPATOCYTES IN VIVO

Abstract

FLM curves from hepatocytes of regenerating rat liver in vivo were compared at different grain count thresholds. Estimates of cell cycle phases derived from curves with thresholds decreasing from 15 to 1 grain (background 0.2 grains per nuclear area) revealed a prolongation of ts from 6.6 to 9.5 hr, at the expense of tG2M, and tG1, whereas tc remained constant. A similar pattern was observed in FLM curves at various threshold levels for hepatocytes localized in subunits of the liver lobule along the vascular axis from afferent to efferent pole. The shapes of these FLM curves indicated an intralobular gradient of reutilizable labelled material. The use of two different threshold levels is crucial for proper selection of FLM curves to evaluate cell cycle phases in regenerating rat liver: first, a threshold to exclude the autoradiographic background, and a second one to avoid errors due to reutilization of labelled DNA precursors. Each threshold has its own implications for the estimation of cell cycle phases.

Advances in epithelial kinetics—An oral view

“…The cell kinetic bahaviour of small populations is masked by the presence of a large population of older amplifying and postmitotic basal cells, and techniques which do not recognize these subpopulations will be biased accordingly. For synchronous populations, some of which have been outlined in this paper, a modified FLM technique (Rabes et al 1976, Wirsching & Rabes 1977) may have some advantages. There is increasing evidence that an understanding of the behaviour of stem cell populations is of importance and that further techniques and assay systems are required (e.g.…”