Thermal sensitivity of CHO cells with different shapes

Abstract

Corifirmining previous reports, we observed that rounded Chinese hamster ovary (CHO) cells from suspension culture were more resistant to heat kill than flattened CHO cells from monolayer culture. Cell survival was quantitatively described by determining full cell survival curves for flattened versus rounded CHO cells after exposure to 43, 44, 45 and 46°C and calculating the T₀ values. The cell survival responses of the rounded cells were significantly different from those of the flattened cells. Based on the ratio of the T₀ values, the rounded cells were consistently twice as resistant to heat-induced cell death than flattened cells. This difference in cell survival was not explained by a trypsin effect in monolayer cells, or by the amount of time rounded cells were maintained in suspension culture, or technical differences in heat-up and cool-down kinetics, or differences in extracellular pH. The two groups also showed no differences in cell generation times or whole cell protein contents. However, we found that the rounded cells had a lower percentage of cells in the S phase of the cell cycle (40% versus 52%) than the flattened cells, which could account for part of the differential heat-induced cell kill in the flattened versus rounded cells. These data suggest there is a significant association between cell shape and heat-induced cell killing.

Key Words:

• Hyperthermia
• cell shape
• flattened monolayer cultured cells
• rounded suspension cultured cells