Time-Lapse Cinemicrographic Observations of Heated G1-Phase Chinese Hamster Ovary Cells: II. Cell Death, Fusion, and Multipolar Divisions

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Abstract
Two forms of irregular divisions, multipolar divisions and divisions followed by fusions, were evident in Chinese hamster ovary [CHO] cells which were heated [hyperthermia, an anticancer modality] in the G1 phase of the cell cycle following synchronization by mitotic selection. The cells were heated to 1 of the following temperatures: 41.5.degree. C for 200 min, 43.5.degree. C for 50 min, and 45.5.degree. C for 12.5, 17.5 or 20.0 min. The frequency of irregular divisions was highest in the earliest generations following heating and 10-fold greater for the severest treatment compared to the mildest. Most of the irregular events were multipolar divisions which occurred without preceding fusion. Frequently fusions of daughter cells followed multipolar divisions. The generation times and mitotic times of cells, which completed generations in which irregular divisions took place, were prolonged but not to any greater extent than those of heated cells arising from regular divisions. Cell death occurred more frequently in interphase than in mitosis. The time of cell death was quite variable but generally extended from 20-50 h after the previous mitosis.

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