AQUAPORINS IN COMPLEX TISSUES - DISTRIBUTION OF AQUAPORIN-1-5 IN HUMAN AND RAT EYE

Multiple physiological fluid movements are involved in vision. Here we define the cellular and subcellular sites of aquaporin (AQP) water tr ansport proteins in human and rat eyes by immunoblotting, high-resolut ion immunocytochemistry, and immunoelectron microscopy. AQP3 is abunda nt in bulbar conjunctival epithelium and glands but is only weakly pre sent in corneal epithelium. In contrast, AQP5 is prominent in corneal epithelium and apical membranes of lacrimal acini. AQP1 is heavily exp ressed in scleral fibroblasts, corneal endothelium and keratocytes, an d endothelium covering the trabecular meshwork and Schlemm's canal. Al though AQP1 is plentiful in ciliary nonpigmented epithelium, it is not present in ciliary pigmented epithelium. Posterior and anterior epith elium of the iris and anterior lens epithelium also contain significan t amounts of AQP1, but AQP0 (major intrinsic protein of the lens) is e xpressed in lens fiber cells. Retinal Muller cells and astrocytes exhi bit notable concentrations of AQP4, whereas neurons and retinal pigmen t epithelium do not display aquaporin immunolabeling. These studies de monstrate selective expression of AQP1, AQP3, AQP4, and AQP5 in distin ct ocular epithelia, predicting specific roles for each in the complex network through which water movements occur in the eye.