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

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Abstract
FLM [frequency of labeled mitosis] 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 15-1 grain (background 0.2 grains/nuclear area) revealed a prolongation of tS from 6.6-9.5 h, 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 labeled material. The 2 different threshold levels crucial for proper selection of FLM curves to evaluate cell cycle phases in regenerating rat liver were a threshold to exclude the autoradiographic background and a 2nd one to avoid errors due to reutilization of labeled DNA precursors. Each threshold has its own implications for the estimation of cell cycle phases.
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