Clonal osteoblast-like cells derived from a rat osteogenic sarcoma (UMR 106–06) were shown to possess specific, high-affinity binding sites for insulin, with a receptor density of 22,000/cell. The hormone, at physiologic concentrations (1–10 ng/ml), was found to stimulate active K+ transport into these cells, the effect being mediated via the Na+-K+ pump. Alterations in insulin-receptor status by treatment of cells with glucocorticoids or exposure to subphysiologic pH was reflected in parallel changes in the sensitivity of the K+-uptake process to the hormone. We conclude that insulin can directly affect the metabolism of bone cells and that the hormone's action on transmembrane ion transport may be linked to interaction with its cell surface receptors.

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