Calcium Rises Abruptly and Briefly Throughout the Cell at the Onset of Anaphase

Continuous measurement and imaging of the intracellular free calcium ion concentration (Ca2+i) of mitotic and interphase PtK1 cells was accomplished with the new fluorescent Ca2+ indicator fura-2. No statistically significant difference between basal Ca2+i of interphase and mitotic cells was detected. However, mitotic cells showed a rapid elevation of Ca2+i from basal levels of 130 nM to 500 to 800 nM at the metaphase-anaphase transition. The Ca2+i transient was brief, lasting approximately 20 seconds and the elevated Ca2+i appeared uniformly distributed over the entire spindle and central region of the cell. The close temporal association of the Ca2+i transient with the onset of anaphase suggests that calcium may have a signaling role in this event.