A cell line from a F344 rat osteosarcoma induced by serial injections of ³²p was established. This cell line, designated MSK, has been maintained for many passages for over 4 years. In the present experiment we investigated a variety of biological properties of the cultured cells.
MSK culture cells had a logarithmic doubling time of 18 h, and exhibited a plating efficiency of 15.7 % even after being cultured for 3 years. The modal chromosome number of the MSK cell line was 56 in the 9 th and 53 in the 45 th and 107 th passages.
Morphologically, the cultured cells had fusiform or polygonal features with multiple cytoplasmal projections in the growing state, and became smaller, more epithelioid when crowded against each other without contact inhibition.
By transmission electron microscopy, the fine structure of MSK cells showed an elliptoid or flattened shape with large nuclei. Prominent cytoplasmic structures with well-developed mitochondoria, and both rough and smooth endoplasmic reticula were observed, but a dilated rough endoplasmic reticulum was rarely seen. Numerous cross-banding typical collagen fibrils and matrix vesicle-like structures were frequently seen among the culture cells. Energy dispersion X-ray analysis of these vesicles revealed peaks for calcium and phosphorus.
MSK culture cells possessed high alkaline phosphatase activities, as much as 10 times more than Hela S3 cells, and these activities have been retained through many passages. The culture cells also showed the accumulation of cyclic AMP upon the addition of parathyroid hormone (PTH 1-84 human) to the culture medium; the production of cyclic AMP was dependent on concentrations of h-PTH ranging between 10-9 and 10-7M.
MSK cells were tumorigenic when transplanted into F344 inbred rats. Histologically, the induced tumors showed characteristic features of osteosarcoma, producing extensive areas of calcification. The ability of the culture cells to calcify in tumors has not decreased throughout the long-term repeated passages.
These results suggest that the MSK cell line is a useful tool not only for the investigation of the characteristics of osteosarcoma, but also for attaining a clearer understanding of the role of the osteoblast on bone metabolism.