Calcium sensitivity of microtubules changes during the cell cycle of Xenopus laevis tadpole endothelial cells

Endothelial cells derived from Xenopus tadpole hearts (XTH-2: Schlage et al. 1981) have been permeabilized for calcium using the ionophore A 23187. A Ca2+-concentration of 1 microM causes a graded disassembly of microtubules (mts): with increasing periods of incubation mts disintegrate and then depolymerize completely. The frequency of the different stages of depolymerization depends on the length of the Ca2+ incubation period, even after 60 min incubation time some mts remain. The stage of depolymerization of mts in a cell is correlated with its cell cycle phase showing the highest stability during S phase.