Osmotic water permeability of rabbit corneal endothelium and its dependence on ambient concentration

We measured the fluid flow osmotically induced by sucrose concentration differences across the isolated rabbit corneal endothelium to determine if its osmotic water permeability, Pos, depends on the concentrations on both sides as well as on the concentration difference across that tissue. We found that when the osmotically induced fluid flow went from stroma to aqueous, Pos decreased from 35 +/- 4 mum/s to 20 +/- 3 mum/s when an additional 20 mosM sucrose was added to the solutions on both sides of the endothelium. However, when the osmotically induced fluid flow was towards the stroma, Pos remained practically unchanged. (28 +/- 4 mum/s vs. 31 +/- 5 mum/s), when additional 20 mosM sucrose was present on both sides. These changes in the measured permeability are consistent with the possibility that sucrose would be swept into the intercellular channels by the osmotically induced fluid flow. We also confirmed that an osmotic gradient can 'prime' the fluid pump. After a gradient was removed, gradients which had previously induced flow from stroma to aqueous caused an increase in the basal fluid pump rate, while gradients in the opposite direction decreased that fluid pump rate.