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Effects of Hyperthermia (41.5°) on Chinese Hamster Ovary Cells Analyzed in Mitosis¹

Departments of Radiology and Radiation Biology [R. A. C., W. C. D.] and Biochemistry [R. A. C., J. R. B.], and the Graduate Faculty of Cellular and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523

The mitotic cells from an asynchronous population of Chinese hamster ovary cells exposed to 41.5° for 7 hr were examined by light and electron microscopy to determine if there were any morphological abnormalities related to cell death or lengthening of metaphase induced by hyperthermia. All components of the mitotic apparatus were formed during exposure to heat, and the mitotic apparatus was functional as demonstrated by eventual cell division. However, heat caused the nuclear envelope to reform precociously around the chromosomes except in the region of the kinetochores, and the nuclear envelope remained associated with the chromatids during segregation. The precocious reformation of the nuclear envelope may be responsible for the lengthening of metaphase. Cells undergoing mitosis during the heat treatment possessed large evaginations of the plasma membrane, and the ubiquitous cortical microfilaments were absent in the region of these evaginations. Possibly related to the membrane damage were osmotic changes resulting in swollen mitochondria observed in heated cells entering mitosis. Since hyperthermic damage to the plasma membrane-microfilament complex was not observed in interphase cells or in cells completing division but was morphologically expressed during mitosis, the thermal lability of the plasma membrane must increase as the cells enter mitosis.

¹ This investigation was supported in part by Grants CA 18334 and CA 09236 awarded by the National Cancer Institute and by Grant RR00592 from the Division of Research Resources, Department of Health, Education, and Welfare.

² To whom requests for reprints should be addressed.

Received 10/ 2/78. Accepted 2/15/79.