Presence of CFTR in the conjunctival epithelium

To determine the presence of the cystic fibrosis transmembrane conductance regulator (CFTR) in the conjunctiva and examine the possibility of its regional expression in rabbit, rat and porcine conjunctival epithelia given distinct differences in morphological appearance between the bulbar and palpebral epithelia.

Two specific anti-CFTR antibodies, against different epitopes in the R domain of the CFTR molecule were used in immunofluorescent labeling of frozen fixed sections isolated from the bulbar and palpebral regions of fresh rabbit, porcine and rat conjunctivae. CFTR expression was also determined in the rabbit conjunctival epithelium using RT-PCR methods.

CFTR immunoreactivity in the conjunctival epithelium exhibits polarized expression and is associated with the apical domain of conjunctival epithelial cells. An identical pattern of staining obtained in porcine cryosections using either of the anti-human CFTR antibodies confirmed the specificity of the positive apical staining. RT-PCR analysis produced bands at the predicted size for CFTR mRNA transcripts in both bulbar and palpebral portions of the rabbit conjunctival epithelium.

Apical localization of CFTR in the conjunctival epithelium is consistent with the function of this protein as a chloride channel or as a regulator of channel activity. The identification of CFTR in both bulbar and palpebral portions of the conjunctiva provides evidence that the mechanisms for Cl secretion reside throughout the conjunctiva. This finding suggests that manipulations of the CFTR Cl channel could affect transepithelial Cl transport rates and water movement into the tear film.