Differential heat sensitivity of normal and transformed Syrian golden hamster embryo cells in confluence

The heat sensitivities of normal and transformed cells derived from Syrian golden hamster embryo (SHE) cells were investigated. There were no differences in heat sensitivities between normal and transformed cells when they were exponentially growing. When confluent cultures were heated in situ, only normal cells showed a reduced heat sensitivity, 4-5 times less than that of exponentially growing cells. However, when these confluent cultures were trypsinized, diluted in medium and heated in suspension, the difference disappeared. When mixed cultures of normal and transformed S11 cells in confluence were heated at 43 degrees C, transformed S11 cells were selectively killed. The induction of HSP70 synthesis by heating in normal SHE cells and transformed counterparts were investigated in confluence using monoclonal antibody. The rate of enhanced HSP70 synthesis after heat treatment did not correlate with the difference in heat sensitivities between normal and transformed SHE cells in confluence as measured by cell survival. The results that normal SHE cells become more resistant to heat than their transformed counterparts only in confluence suggest that cell-to-cell contact plays an important role in the heat resistance of normal SHE cells in vivo.