Effect of mannitol on the permeability of cultured endothelial cells

The effect of mannitol on the permeability of the endothelial monolayer was investigated. Endothelial cells from bovine major cerebral arteries were cultured on a polycarbonate membranes of the double chamber culture system. After the monolayers reached confluence, they were incubated with three kinds of mannitol solution either on the upper chamber or the lower chamber. Evan's blue conjugated bovine serum albumin was used as a marker of vasopermeability and added into the upper chamber solution. The density of the dye that passed through the monolayer was measured by a spectrophotometer. When the solution of the lower chamber was Hepes buffered salt solution (HBSS), permeability was maximum with the 20% mannitol solution in the upper chamber. When the solution of the lower chamber was 20% mannitol, permeability was maximum with HBSS in the upper chamber. When the solution of the lower chamber was 10% mannitol, permeability was minimum with the 10% mannitol solution in the upper chamber. These findings suggested that endothelial cells increase vasopermeability according to gradient of the concentration of mannitol between the intraluminal side and the abluminal side, and not due to the hyperosmolarity itself. Hyperosmolar urea made the endothelial cells shrink, while hyperosmolar mannitol solution did not induce such shrinkage. Therefore a difference in the mechanism of increasing vasopermeability by mannitol and urea was suggested.