Molecular identification of functional water channel protein in cultured human nonpigmented ciliary epithelial cells

Purpose. Water channel proteins are important pathways for water movements across cell membranes, including those in the ciliary epithelium, which is the major site of aqueous humor secretion. In this study, we aimed to demonstrate the expression of functionally active aquaporin-1 (AQP1) water channels in cultured human ciliary epithelial cells. Methods. Poly A⁺ RNA was isolated from cell cultures of Simian Virus 40 (SV-40) transformed human nonpigmented ciliary epithelium (NPE) subjected to RT-PCR reaction using primers specific to AQP1. Northern analysis was used to define the expression of AQP1 in NPE cells. Western immunoblotting with polyclonal antibody raised against AQP1 was used to evaluate the AQP1 protein expression in the plasma membranes of human NPE cells. Light scattering method was used to determine the osmotic water permeability in the suspension of NPE cells. Results. RT-PCR using specific primers for AQP1, Northern analysis and Western immunoblot using AQP1 specific antibody demonstrated the expression of AQP1 in the plasma membranes of NPE cells. Osmotic water permeability (P(f)) measurements confirmed that functional AQP1 water channels are expressed in human NPE cells and the P(f) for these cells was 9.8 x 10^-3 cm/s at 10°C. Conclusions. The presence of AQP1 in human NPE cells suggests that it may have a role in the fluid flow across epithelial membranes. In addition, the existence of AQP1 in the human NPE cells provide an excellent in vivo model to study the regulation of aquaporins and their possible role in the aqueous humor secretion.