The permeability of the apical and basolateral membrane of rat corneal endothelial cells to water and urea was studied. It was shown that the apparent water permeability of the basolateral membrane of endothelial cells (4.43E-05 ± 7.57E-07 cm/s) is more than three times higher than the permeability of the apical membrane (1.21E-05 ± 1.03E-07 cm/s). The permeability of the basolateral membrane of endothelial cells to urea (1.23E-04 ± 1.56E-06 cm/s) was higher than the permeability of the apical membrane (9.52E-05 ± 1.02E-06 cm/s) by 30%. The contribution of phloretin-inhibited urea transport across the apical and basolateral membrane in these cells was studied. Phloretin at a concentration of 0.1 mM reduced the urea permeability by more than 20% through both the apical and basolateral membranes. The results suggest that the compositions of the transporters involved in water transport in the apical and basolateral membranes differ significantly. It is suggested that the high apparent water permeability of the basolateral membrane of endothelial cells could be explained by the contribution of concomitant water transport with ions involved in active transport processes. The presence of phloretin-sensitive urea transporters in the plasma membrane of endothelial cells that could take a part in urea transcellular movement, has been shown. The results indicate the possible importance of urea for corneal function.
Katkova et al. (Wed,) studied this question.