Cytologic and genetic features of mammalian cultured cells adapted to hypertonic medium

The response to changes in the osmotic pressure and the capability to adapt to raised tonicity of culture medium, obtained by increasing the NaCl molarity (0.137M), varies among different Mammalian cell lines. Cells cultured in permissive hypertonic medium become resistant to more drastic hypertonic solutions, which are incompatible with cell survival, in the absence of any pretreatment. When cells grown in hypertonic medium are fed again with normal medium, they do not maintain their greater resistance acquired by adaptation; this points to a reversible physiological process rather than to a stable regulatory change at a genetic level. Cells of the EUE line (human embryonic epithelium), grown in medium containing a doubled NaCl concentration (0.274M), show a growth rate slower than cells cultured in a isotonic medium, whereas the plating efficiency is apparently unaffected. The chromosome number distribution in EUE cells cultured in hypertonic medium shows a significant increase in the frequency of cells with a double chromosomal set (20% in treated cells versus 1.5% in control cells). The induction of polyploidy in hypertonic media can be a useful tool in experiments of genetic analysis based on chromosome segregation via tetraploidy. Furthermore the osmotic adaptation of cells in vitro can provide a useful selective system for the isolation of cellular hybrids.