Altered biochemical properties of mitochondria in mouse mammary epithelial cells during primary culture

Various biochemical properties of mitochondria isolated from primary monolayer cultures of mammary epithelial cells from mid‐pregnant or hormonally stimulated mice were examined daily for seven or eight days. When compared with mitochondria from mammary glands of mid‐pregnant animals, the specific activities of several mitochondrial enzymes were greatly reduced in cells after seven days in culture. There was a 5‐ to 6‐fold reduction in the specific activities of cytochrome oxidase, succinate dehydrogenase and α glycerophosphate oxidase while malate dehydrogenase and adenylate kinase activities were 2‐ to 3‐fold lower. The reduction in mitochondrial enzyme activities was gradual and related to the length of time the cells were in culture. Progressive changes were also seen in the electrophoresis profiles of mitochondrial proteins in SDS‐urea polyacrylamide gels. Mitochondria isolated from 1‐, 2‐, 3‐ and 8‐day cell cultures showed a continuous reduction in the relative amounts of several mitochondrial polypeptides in the gel profiles. Addition of 35 S‐methionine to cell cultures for short and long periods indicated that mitochondrial protein synthesis continued throughout the 8‐day culture period. However, the synthesis of several particular polypeptides was reduced progressively during the culture period. These studies indicate that mouse mammary epithelial cells have a lowered capacity for respiratory metabolism as a result of specific mitochondrial alterations which might be associated with the general loss of differentiated morphology by those cells during monolayer culture.