Regulation of the retinal interphotoreceptor matrix Na by the retinal pigment epithelium during the light response.

We examined the rabbit retinal pigment epithelium (RPE) for Na transport properties which would allow it to buffer undesirable changes in Na concentrations in the interphotoreceptor matrix (IPM) during light and dark cycles. The RPE is selectivity permeable to sodium. Open and short circuit transport studies with RPE indicate a circulating (choroid to retina and back) Na current which does not compromise the electrical integrity of the blood brain barrier but together with the Na permselectivity is of sufficient magnitude to buffer both upwards and downwards movements of IPM [Na] during light or dark responses.