Ouabain-induced cell proliferation in cultured rat astrocytes

Ouabain markedly stimulated not only [H-3]thymidine incorporation but also [H-3]uridine incorporation into astrocytes. The effects were observed at 36-48 hr and 12-72 hr after addition of ouabain, respectively. The dose-response curves were both bell-shaped types with a peak at 10(-3) M for thymidine incorporation and 2 x 10(-3) M for uridine incorporation. Ouabain increased cell number as determined by an assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and by a method using a hemocytometer. Low concentration of external K+ mimicked the effect of ouabain in stimulating [H-3]thymidine incorporation, and high concentration of external K+ blocked the effect of ouabain. In contrast to astrocytes, ouabain did not stimulate [H-3]thymidine incorporation into C6 glioma and fibroblast cells. The effect of ouabain on [H-3]thymidine incorporation in astrocytes was dependent on external Ca2+, and it was blocked by cycloheximide. These findings indicate that prolonged Na+,K+-ATPase inhibition causes cell proliferation in cultured astrocytes in cell-specific and Ca2+-dependent manners.