[Electron microscopic morphometric study of activated chromatin of lymphocytes. I. Variation of chromatin condensations during early action of phytohemagglutinin].

We made a quantitative electron microscopic investigation of rat blood lymphocyte chromatin on cell sections in the early period of action of phytohaemoagglutinin (PHA). According to the dynamics of binding of acridine orange to chromatin, there were chosen time lapse after the beginning of stimulation of cells. In one hour of PHA action when the binding of acridine orange is intensified two-fold the total area of profiles of condensed chromatin was not changed, however, the area of membrane-free chromatin profiles was simultaneously diminished by 36%. At that period, the packing of DNP-fibers of condensed chromatin loosened. After 1.5 hr, parallel to a noticeable decrease of binding of acridine orange, there were observed tendencies for restoration of area of chromatin profiles and partial diminishing of relative distances between DNP-fibers. In 6 hrs, the binding of acridine orange was sharply intensified, which was accompanied by a decrease by 26% of the total area of chromatin profiles at the expense of diminishing of perimembranous chromatin. At the same time, the low-electron--density regions of condensed chromatin were enlarged, and the packing of DNP-fibers was strongly loosened.