Transition from metaphase to anaphase is accompanied by local changes in cytoplasmic free calcium in Pt K2 kidney epithelial cells
We have used a Ca2+-sensitive dye, fura-2, to investigate the role of Ca2+ during mitosis in Pt K2 epithelial cells. The concentration of cytoplasmic free calcium, [Ca2+]i, increased 2-fold between metaphase and anaphase. Digital image analysis revealed two patterns of [Ca2+]i localization during anaphase. In half of the anaphase cells, the increase in [Ca2+]i was greatest in the region near the spindle poles and decreased radially. In the other anaphase cells, there was a ring of high [Ca2+]i in the cytoplasm, surrounding an area of low [Ca2+]i in the spindle midzone. Although the reason for the different patterns is not known, peak [Ca2+]i in both cases was sufficient to maintain a 2- to 6-fold gradient in [Ca2+]i from the polar region to the midzone. [Ca2+]i gradients may thus regulate spindle microtubule equilibria and directed chromosome movement during mitosis.