The epithelial sodium channel (ENaC) in rodent retina, ontogeny and molecular identity

Purpose. To assess the appearance of the epithelial sodium channels (ENaC) during retinal development and establish its molecular identity. Methods. Photoreceptors were isolated by horizontal sectioning of rat retin a with a vibratome series 1000. Intact retina and isolated photoreceptors w ere analyzed for the developmental appearance of ENaC using the Polymerase Chain Reaction (PCR) technique. Immunofluorescence was conducted with the a id of an antibody raised against the 14 amino acids peptide QGLGKGDKREEQGL, corresponding to the N-terminal region (44-58 aa) of alpha ENaC. Results. ENaC message was present in rat retina photoreceptors, isolated ju st one day after birth. The bipolar and ganglion cell layers, separated fro m whole retina by vibratome, also contained the ENaC message. The partial s equence of the photoreceptor ENaC (496 base) exhibited one hundred percent homology with the channel from rat known sources. Immunochemistry revealed that only the outer nuclear layer was positive for the ENaC in one-day-old rat; the inner segment became immunopositive at the age of 9 days. Conclusion. The ENaC is present in the retina and visible soon after birth. These observations suggest that ENaC may prove to have physiological impor tance in the retina but until now its function is unknown.