Rate of increase of osmolality determines osmotic tolerance of mouse inner medullary epithelial cells

Renal inner medullary cells survive and function despite interstitial osmolality of 600-1,700 mosmol/kgH(2)O or more. In contrast, much smaller changes kill cells in tissue culture. Using mouse inner medullary epithelial cells at passage 2, we defined factors that might account for the difference. Most of the factors that we tested, including addition of hormones (insulin-like growth factor I, epidermal growth factor, or deamino-8-D-arginine vasopressin), growth on porous supports, and presence of matrix proteins (collagen I, collagen IV, fibronectin, laminin, or fibrillar collagen I), have no significant effect. However, the time course of the change makes a major difference. When osmolality is increased from 640 to 1,640 mosmol/kgH(2)O by addition of NaCl and urea in a single step, only 30% of cells survive for 24 h. However, when the same increase is made linearly over 20 h, 89% of the cells remain viable 24 h later. We conclude that gradual changes in osmolality, e. g., in vivo, allow cells to survive much greater changes than do the step changes routinely used in cell culture experiments.