Modulation of osmolytes in MDCK cells by solutes, inhibitors, and vasopressin

MDCK cells accumulate organic osmolytes in response to hyperosmotic NaCl-supplemented medium. We examined time course and inhibitor sensitivity of myo-inositol, sorbitol, and glycerophosphorylcholine (GPC) accumulation in MDCK cells exposed to hyperosmotic NaCl-, D-glucose-, or mannitol-supplemented media. In NaCl medium, cells preferentially accumulated inositol and GPC. In comparison, in glucose medium cells preferentially accumulated sorbitol and GPC. Inositol demonstrated a late (72-96 h) accumulation in glucose medium, although less than in NaCl medium. Mannitol medium did not significantly stimulate accumulation of any of these three osmolytes at 24 h, suggesting that hyperosmolality alone is not sufficient stimulus for their accumulation in this time frame. GPC accumulation was very rapid in glucose medium, and fell to the level induced by NaCl medium at 96 h (approximately 50 nmol/mg protein). Inositol and sorbitol accumulated more gradually, each reaching greater than 400 nmol/mg protein after 96 h. Sorbitol was still accumulating at 96 h, whereas inositol plateaued at 72-96 h. Phlorizin or sorbinil blocked accumulation of inositol or sorbitol, respectively. Sorbitol and GPC accumulation in glucose medium were partially inhibited in absence of serum or in presence of 1 microM vasopressin. Thus NaCl and glucose appear to stimulate specific cellular mechanisms responsible for accumulation of inositol, sorbitol, and GPC in MDCK cells. This accumulation is also modulated by constituents of serum.