Benign Pleural Mesothelial Cells Have Higher Osmotic Water Permeability than Malignant Pleural Mesothelioma Cells and Differentially Respond to Hyperosmolality

Background/Aims: Cell volume regulation is a critical mechanism for cell homeostasis and depends on the osmotic water permeability (P_f) of the cell plasma membrane. The P_f of human mesothelial cells is unknown although they contribute to serosal fluid turnover. Methods: In this study we measured the osmotic water permeability of benign human mesothelial cells (MeT-5A) and of epithelioid (M14K) and sarcomatoid (ZL34) malignant pleural mesothelioma (MPM) cells in response to acute hyperosmotic stress. We also assessed the changes in their P_f after preconditioning with 4% glucose for 24 hours. In both cases we also assessed the role of AQP1 inhibition (0.1 mM HgCl₂) on the P_f. Finally, we assessed corresponding changes in the AQP1 plasma membrane availability by immunofluorescence. Results: We report that MeT-5A cells have a significantly higher P_f as compared to M14K and ZL34 MPM cells [4.85E-03±2.37E-03 cm/sec (n=17) versus 2.74E-03±0.74E-03 cm/sec (n=11) and 2.86E-03±0.11E-03 cm/sec (n=11)]. AQP1 inhibition significantly decreased the P_f in all cells lines (p<0.001 in all cases). High glucose preconditioning for 24 hours significantly increased MeT-5A P_f (p<0.001), did not influence M14K P_f (p=0.19) and significantly reduced ZL34 P_f (p=0.02). Comparing cell lines after high glucose preconditioning, MeT-5A P_f was significantly higher than that of M14K and ZL34 MPM cells and the AQP1 inhibition effect was significant in MeT-5A and M14K cells. These results were corroborated by AQP1 immunofluorescence. Conclusion: We provide evidence for a differential regulation of P_f in benign and MPM cells that require further mechanistic investigation.