Hypoxia increases cell death in multidrug-resistant leukemia cells. Differences in viability and ultrastructure...

The comparative study of sensitive and multidrug-resistant L1210 cells under 24 hours of hypoxia (2% O2 and 5% CO2 at 37 degrees C) was done to see if differences in energetic metabolism between both cell lines are paralleled by differences in cellular morphology. During the dye exclusion assay the viability of sensitive cells was about 70 to 90%, whereas only 30 to 50% of resistant cells were viable. Electron microscopic study of sensitive and resistant L1210 cells under hypoxia has shown cells of different ultrastructural appearance in both cell lines. Cells with necrotic changes (swollen mitochondria, lysed cells) prevailed in resistant cells. The highest incidence of cells with normal or slightly dense mitochondria was found among the sensitive L1210 cells. Additionally, cells with pyknotic nuclei, shrunken cytoplasm and dense mitochondria, reminiscent of apoptosis, could be found sporadically, especially in the sensitive L1210 cell line. These results are in agreement with flow cytometry measurements: in resistant cells the number of necrotic cells was on the average 2.3 times higher than in sensitive cells. Ultrastructural differences and differences in the numbers of necrotic cells as measured by flow cytometry between sensitive and resistant L1210 cells under hypoxia are consistent with differences in energetic metabolism between these cell lines, as described in earlier studies, and document an increased cell death in the resistant L1210 cell line.