[The isolation and phenotypic characteristics of heat-resistant cells from the Chinese hamster CHO-K1 line]

By sequential selection for a resistance to a short-term heating at 45 degrees C, two independent clones, CHSR5 and CHSR6, have been isolated from ovarian cells of the Chinese hamster (CHO-K1). A subline CHO-A40, capable of proliferation at 40 degrees C, has been obtained as mass culture by culturing CHO-K1 cells for 2 months at 40 degrees C. The lines obtained have no cross-resistance to the temperature used in their selection: the CHSR5 and CHSR6 cells are not capable of reproduction at 40 degrees C, while the CHO cells do not survive over a 60 min heating at 45 degrees C. This bears evidence that mechanisms, underlying the cell resistance under different thermal regimens used, may be different. The heat resistant sublines maintain their heat resistance for 6 months of cultivation at 37 degrees C. The acquisition of heat resistance by cells correlates with their high primary resistance, and with their resistance to colchicine and actinomycin D.