Changes in volume of peritoneal mesothelial cells exposed to osmotic stress

Objective: To evaluate changes in volume of mesothelial cells exposed to hypertonic medium and the role of volume regulatory mechanisms in adaptation to hyperosmotality. Design: Experiments were performed on primary cultures of human peritoneal mesothelial cells. Cell volume was estimated by measuring equilibrated (intracellular/extracellular space) ¹⁴C-urea in cellular water. Cells in monolayers were exposed to hyperosmotic media and changes in cellular water or intracellular uptake of ³H-proline were measured. Results: Exposure of mesothelial cell monolayers to hyperosmotic media reduced the cell volume; the effect was proportional to the osmolality of the medium. Volume of cells exposed to medium supplemented with glucose (180 mmol/L) decreased by 26%, p < 0.001, after 30 minutes' incubation. Prolonged exposure of mesothelial cells to hyperosmotic medium resulted in gradual recovery, after initial decline, of their volume. Intracellular uptake of amino acid ³H-proline increased after 240 minutes' exposure of the mesothelial cells to medium supplemented with glucose (90 mmol/L) (+40%, p < 0.05). When cells cultured for 7 days in medium supplemented with glucose (45 mmol/L) were exposed to medium with low glucose content (5 mmol/L) their volume increased by 77%, p < 0.05. Conclusion: Mesothelial cells shrink after exposure to hypertonic medium. Increased intracellular uptake of amino acids may be one of the regulatory mechanisms that ensure subsequent volume increase in these cells. Mesothelial cells chronically exposed to hypertonic medium swell after transfer to a medium with physiologic osmolality.