Intracellular free calcium levels are reduced in mitotic Pt K2 epithelial cells

Using a fluorescence ratio method, we have studied the intracellular free calcium levels in individual quin-2-loaded mitotic cells under the microscope. We have found that intracellular free calcium concentrations in Pt K2 epithelial cells drop by approximately 50% as they pass through mitosis. Calcium levels in interphase cells were 53 +/- 7 nM. During prophase, free cytoplasmic calcium begins to decrease, reaching 28 +/- 3 nM in prometaphase. Calcium levels remain low until the nuclear envelope is re-formed in late telophase, when they increase again to interphase levels. This decrease in overall free calcium in mitosis suggests that the mitotic cell has mechanisms for the general sequestration, and perhaps local release, of calcium ions.