Regulation of epitectin production in a malignant cell line.

RT112 cells, a line derived from a human bladder carcinoma, produce epitectin at very low levels in standard culture media; but production and secretion of this mucin are greatly increased when the cells are exposed to hyperosmotic conditions. It appears that hyperosmolarity, by inducing an increase in intracellular sodium, entrains an increase in intracellular free calcium. Evidence is presented for the view that it is the increase in intracellular free calcium that provides the more direct stimulus for the enhanced production of epitectin.