Interrelationships between the retinal pigment epithelium and the neurosensory retina

The role of the retinal pigment epithelium in regulating transport between the choriocapillariss and sensory retina was studied by examining the diffusion fluorescent across the intact rabbit retinal pigment epithelium and the retinal pigment epithelium damaged by intravenous injection of sodium iodate. Destruction of the tight junctions of the retinal pigment epithelium allowed free diffusion of fluorescein from the choroid into the retina. The electrical characteristics of the cat retinal pigment epithelium which play an important role in governing transport of substances across the retinal pigment epithelium were studied. The apical membrane of the cat retinal pigment epithelium resembled that of the frog in having high sensitivity to apical K+, greater sensitivity to apical Na+, and less sensitivity to apical HCO3-. The apical membrane was sensitive to oubain which produced a rapid fall in the transepithelial potential. Previous studies of the electrical properties of the retinal epithelium in cold blooded preparations are summarized with emphasis on the important interactions between the retinal pigment epithelium and sensory retina and the implications that these studies have with regard to the regulation of photoreceptor function.