Cultured bovine corneal epithelial cells express a functional aquaporin water channel

PURPOSE. Given recent physiological and in situ hybridization evidence for the presence of a water channel in corneal epithelium, this study was condu cted to investigate its expression and characteristics using cultured bovin e corneal epithelial cells (CBCEPCs). METHODS. CBCEPCs were grown in DMEM containing 2 ng/ml fibroblast growth fa ctor and 6% fetal bovine serum. To determine their osmotic permeability (P- f), cells were passaged onto rectangular glass coverslips, and anisotonical ly induced volume changes were monitored by light scattering. To investigat e expression, poly(A(+)) RNA from CBCEPCs was injected into Xenopus laevis oocytes, and the P-f of the oocytes was determined. RESULTS. For CBCEPCs challenged with a 10% hypotonic solution at 37 degrees C, the kinetic constant of volume change was k = 0.52 +/- 0.04 seconds(-1) , and the calculated P-f 72 +/- 6 mu m/sec (n = 16). The P-f of oocytes inj ected with water was 14 +/- 1.8 mu m/sec (n = 4); injection with poly(A(+)) RNA from CBCEPCs increased P-f to 77 +/- 6 mu m/sec (n = 6). This increase in P-f was inhibited by 72% (reduced to 22 +/- 1 mu m/sec) by 0.3 mM HgCl2 and was inhibited by 56% to 58% by coinjection with aquaporin (AQP)5 antis ense oligonucleotide. CONCLUSIONS. The comparatively high P-f determined for CBCEPCs, the presenc e of mRNA encoding water channels, and sensitivity to mercurial agents are typical of the expression of functional water channels. The predominant mes sage is for AQP5, although the evidence was consistent with the presence of additional water channels. These findings bring renewed support for the no tion that the epithelium can contribute to corneal hydration homeostasis.