IS THERE A CELL-TO-CELL CONTACT EFFECT ON THE X-RAY DOSE-SURVIVAL RESPONSE OF MAMMALIAN-CELLS

While a cell-to-cell contact effect has been reported for a Chinese ha mster subline V79-171B, this was not observed for another subline V79 171-S. Therefore, we tested whether the cell-to-cell contact effect on cell survival depended on the cell line or the experimental condition s used. We have cultured and compared both sublines under identical co nditions. Both sublines, cultured in Eagle's minimal essential medium (MEM) with 15% serum, had nearly identical cell doubling times and rad iosensitivities. For both sublines, the survival of spheroid and monol ayer cells subcultured immediately after irradiation were nearly the s ame, i.e., a radioprotective contact effect for spheroid cells was abs ent. Under conditions favorable for the repair of radiation induced da mage, cell survival was higher for cells in monolayers than for cells in spheroids. Potentially lethal damage (PLD) repair and sublethal dam age (SLD) repair were present in both sublines. However, the magnitude of expression of PLD by hypertonic saline was higher for monolayer th an for spheroid cells. We conclude that: 1) the reported differences b etween V79 sublines (contact effect on survival) appear to be dependen t on differences between experimental conditions rather than on cell t ype; 2) delayed plating technique does not detect PLD repair in round spheroid cells; and 3) detection of repair by split dose is independen t of cell shape and/or two- or three-dimensional culture conditions.