FLOW CYTOMETRIC STUDY OF CHANGES IN THE INTRACELLULAR FREE CALCIUM DURING THE CELL-CYCLE

We measured the intracellular levels of free cytoplasmic calcium in di fferent phases of the cell cycle in viable rat fibroblasts, using two parameter now cytometric analysis with Hoechst 33342 as the DNA specif ic dye and Fluo-3 as the calcium sensitive dye. We studied changes in calcium levels during the G1 phase of cell cycle by arresting cells wi th chemical agents such as staurosporine and hydroxyurea or by density dependent arrest of cell growth. We show that levels of calcium are l owest at the beginning of G1 phase but rise steadily with its progress ion and culminate at the G1/S border, Our results suggest that complex changes occur in calcium levels during the process of mitotic divisio n, During progression of S and G2 phases, calcium levels decline and i ncrease respectively. Our results offer a new methodology to estimate intracellular calcium levels in specific phases of the cell cycle. Bas ed upon these results we propose a general scheme representing the cha nges in the intracellular calcium concentration during the progression of the cell cycle. (C) 1996 Wiley-Liss, Inc.