FIG. 4.
The ciliary epithelial bilayer. The scheme on the left depicts the localization of transport mechanisms and is adapted from McLaughlin et al.31 The model is a simplification since transport activity is not uniform over the ciliary epithelial surface. Electron microprobe analysis of rabbit ciliary epithelium indicates enhanced secretion posteriorly and enhanced absorption anteriorly.32 Aqueous humor flow occurs in the PE-to-NPE direction. The PE and NPE are coupled by gap junctions and function in the manner of a syncytium. Na,K-ATPase activity and protein expression are highest at the basolateral, aqueous humor-facing surface of the NPE. In respect to coupling and Na,K-ATPase distribution, the tissue is similar to the 2-cell model shown in Fig. 1. NPE, nonpigmented ciliary epithelium; PE, pigmented ciliary epithelium.