External Cl(-)-dependent formation of watery vacuoles by long-term hypotonic shock in 3T3-L1 cells

Osmotic shock transiently induces a volume change in the cells, followed by a restoration of the cell volume due to intracellular water regulation. Effect of long-term osmotic shock on the water regulation is not completely understood. Vacuole formation by long-term osmotic shock was investigated to clarify the water exclusion mechanism from cytoplasm into intracellular vacuoles in 3T3-L1 cells. Incubation of cells in hypotonic solution reversibly induced the vacuole formation. Staining of vacuoles with fluorescent dyes revealed that vacuoles were derived from endoplasmic reticulum and Golgi apparatus but not lysosomes. Membrane-impermeable fluorescent dyes were taken up into some vacuoles from cytoplasm and extracellular solution, suggesting that some vacuoles exhibit the dynamic changes for the connection of plasma membrane, and that transporter for membrane-impermeable dyes might be active in some vacuole membranes. External Cl(-), but not Na(+), was required for vacuole formation. DPC suppressed the vacuole formation and increased cell height, and further incubation with DPC increased the number of dead cells. Bumetanide, dimethylamiloride, and HgCl(2) did not suppress the hypotonic stress-induced formation of water vacuoles. These findings suggest that 3T3-L1 cells regulate the intracellular water content through the DPC-sensitive external Cl(-)-dependent vacuole formation during long-term osmotic stress.