A preadipocyte cell line derived from murine bone marrow stroma: characterization of morphological, enzymatic, and functional nature of the cells.

A preadipocyte cell line (K-1) has been established from the adherent cell population of murine bone marrow culture. Using light microscopy, the cells exhibit fibroblast-like morphology and accumulate lipids in their cytoplasm as the cultures become confluent. Ultrastructurally, each cell has a large indented nucleus with prominent nucleoli. The cytoplasm contains a well-defined Golgi complex, numerous mitochondria, some endoplasmic reticulum, microfilaments, and fat droplets. Lysosomal granules are rarely recognizable. Cytochemically, they are positive for acid phosphatase, but negative for nonspecific esterase. Alkaline phosphatase activity is negative to weakly positive. Supernatants from K-1 cell cultures contain granulocyte/macrophage colony-stimulating factors, which stimulate primarily the growth of macrophage colonies, but do not affect proliferation of spleen colony-forming units.