Fluid transport by human nonpigmented ciliary epithelial layers in culture: a homeostatic role for aquaporin-1

We report for the first time that cultured nonpigmented human ciliary epith elial (NPE) cell layers transport fluid. Cells were grown to confluence on permeable membrane inserts, and fluid transport across the resulting cell l ayers was determined by volume clamp at 37 degrees. These cell layers trans located fluid from the apical to the basal side at a steady rate of 3.6 mul .h(-1).cm(-2) (n = 4) for 8 h. This fluid movement was independent of hydro static pressure and was completely inhibited by 1 mM ouabain, suggesting it arose from fluid transport. Mercuric chloride, a nonspecific but potent bl ocker of Hg2+-sensitive aquaporins, and aquaporin-1 antisense oligonucleoti des both partially inhibited fluid transport across the cell layers, which suggests that water channels have a role in NPE cell homeostasis. In additi on, these results suggest that of the two ciliary epithelial layers in tand em, the NPE layer by itself can transport fluid. This cultured layer, there fore, constitutes an interesting model that may be useful for physiological and pharmacological characterization of ciliary epithelial fluid secretion .