Immunocytochemical localization of carbonic anhydrase, NaK-ATPase and the bicarbonate chloride exchanger in the anterior segment of the human eye.

We examined immunohistochemically the localization of three transport enzymes (carbonic anhydrase, Ca-II; sodium-potassium-activated adenosine triphosphatase, NaK-ATPase; bicarbonate-chloride exchanger, band III) in the anterior segment of the human eye. In accord with earlier studies, NaK-ATPase was primarily found in the corneal endothelium, but also in the corneal basal epithelial cell membranes. In addition, immunoreactivity for NaK-ATPase was observed in the non-pigmented epithelium of the ciliary processes and between the two epithelial cell layers. Ca-II immunoreactivity was found in the corneal endothelium as well as in the non-pigmented epithelial layer of the ciliary processes. Interestingly, band III immunoreactivity was found in the corneal endothelium, as similar to Ca-II, but not in the ciliary processes. These results show that, similar to many other tissues, Ca-II and band III immunoreactivities colocalize in the same cytologic site in the human corneal endothelium. Immunocytochemical detection of these key transport enzymes not only gives their accurate and reliable anatomical distribution, but also provides information on the electrolyte transport at these sites.