Microspectrofluorometry of fluorescent photoproducts in photosensitized cells: Relationship to cellular quiescence and senescence in culture

Microspectrofluorometry of L and WI-38 cells reveals chemical/structural changes due to quiescence or senescence, i.e., lipid peroxidation, spontaneous or photosensitized by hematoporphyrin. Cells treated with hematoporphyrin and a lysosomal umbelliferone probe show a fast-rising umbelliferone emission, plus a fluorescent photoproduct. Studies in rapidly growing versus quiescent L, early passage/late passage WI-38 cells, suggest accumulation of fluorescence Schiff bases (i.e., their association with granular regions of cells in stationary phase, spectral properties, fast increase in photosensitized cells) and a possible lysosomal membrane permeabilization in quiescent or senescent cells.     

REPOPULATION OF THE BONE-MARROW STEM-CELL COMPARTMENT AFTER IRRADIATION*

Bone-marrow repopulation has been followed as a function of time after a single whole-body dose of 150 rads X-rays to (C3H × C57B1)F₁ hybrid mice. The number of nucleated cells per bone shaft has been estimated by direct counting and the number of progenitor cells by the exogenous spleen-colony assay method. Vinblastine was also administered under various schedules of time and dose in an endeavour to distinguish between cycling and dormant cells in the progenitor pool. The depopulation of total marrow cells induced by Vinblastine proceeds at a comparable rate in irradiated and in normal mice. On the other hand, the depopulation of the colony-formers is faster in irradiated than in normal animals. The data are interpreted to show that the fraction of cycling progenitor cells is larger in a haemopoietic tissue undergoing numerical expansion.