| Abstract: | The cardiac glycoside ouabain has been shown to stimulate erythroid stem cell (CFU-e/BFU-e) colony formation while inhibiting both granulocyte/macrophage precursor cell (CFU-gm) and murine spleen stem cell (CFU-s) colony formation. We have examined the ability of ouabain to increase both CFU-e/BFU-e colony formation by performing time-delay and temperature-dependent studies. After pre-exposure of marrow cells to ouabain (10(-15) M) at temperatures of 27, 37, or 4 degrees C, erythropoietin (Ep) was added after time-delays ranging from 10 s to 60 min. The ouabain-induced increase in CFU-e/BFU-e colony formation was observed up to an Ep-delay of 20 s, after which time the enhancing effect of ouabain was diminished. This increase was also observed when marrow cells were first exposed to Ep prior to a similar delayed exposure to ouabain. The enhancement effect seen with ouabain was also temperature dependent, since at 37 degrees C an earlier time increase in CFU-e/BFU-e colony formation was observed when compared to identical studies performed at either room temperature or 4 degrees C. These studies suggest that ouabain-induced elevations in erythroid stem cell colony formation involve mechanisms that are both time and temperature dependent. |
