INCREASE OF CALCIUM LEVELS AT INTERPHASE IN NIH 3T3 CELLS

The fluorescent calcium ion indicator dye Fluo-3 and DNA-binding dye H oechst 33342 were employed to determine, in a quantitative microspectr ofluorometric study, the intracellular calcium ion concentration ([Ca2 +]i) and the DNA content of individual living NIH3T3 cells. The well-s eparated excitation and emission properties of these dyes allowed us t o establish for each cell both the phase of the cell cycle using DNA c ontent and [Ca2+]i. We found that the transition from G1, through S, t o the G2 phase is accompanied by a two-fold increase in [Ca2+]i. The [ Ca2+]i was inhomologous in each phase of the interphase (G1, S and G2) although [Ca2+]i in the S and G2 phases was never lower than certain threshold values in the G1 and S phases respectively. [Ca2+]i in G0 ce lls was lower than that in G1 cells. These changes in [Ca2+]i suggest that [Ca2+]i may be an important regulator of cell cycle progression.