Cobalt-tolerance and mucopolysaccharide production in rat dermal fibroblasts in culture

Abstract

1. 1. Monolayer cultures of rat dermal fibroblasts will not normally tolerate doses of cobalt above 2.5 μg Co 2+/ml. 2. 2. By repeated intermittent treatment with cobalt chloride two lines of rat dermal fibroblasts were developed which would tolerate doses of up to 7.5 μg Co 2+/ml. 3. 3. The tolerance thus induced was followed after some months by the development of cytological and metabolic changes. These changes persist for many months after the cessation of cobalt treatment. 4. 4. The cytological characteristics of these “artificially” cobalt-tolerant cultures included great variation in cell size and shape, a high proportion of abnormal mitoses and a marked degree of aneuploidy. 5. 5. The metabolic characteristics included a depressed respiration, an increased glycolysis, and the persistence of hyaluronic acid formation beyond the stage at which it was lost by controls untreated with cobalt. 6. 6. Unlike mucopolysaccharide-producing cells in primary cultures of rat dermal fibroblasts, cobalt-tolerant cells were stimulated to produce more hyaluronic acid by treatment with cobalt chloride. 7. 7. Cobalt-tolerant cells were also stimulated to produce more hyaluronic acid by a reduction in the serum content of the nutrient medium. 8. 8. Cultures of rat dermal fibroblasts which had not been treated with cobalt chloride developed after prolonged cultivation in normal medium an increased tolerance of cobalt. This was accompanied by metabolic changes of the type seen in induced tolerance, but not by cytological changes or hyaluronic acid production. 9. 9. Such “naturally” tolerant cultures could not be induced to form hyaluronic acid either by prolonged cobalt treatment or by reduction of the serum content of the medium. 10. 10. The possible causes of the cytological, metabolic and functional changes in “artificially” cobalt-tolerant cell lines are discussed.