Immunohistochemical localization of Na+/Ca2+ exchanger in human retina and retinal pigment epithelium

Impaired calcium (Ca2+) metabolism has been implicated in the pathogenesis of various ocular diseases, suggesting that regulation of Ca2+ homeostasis in the retina is of major significance for normal function. There are known families of transport proteins that can catalyze net Ca2+ efflux across the plasma membrane, one of which is the Na+/Ca2+ exchanger. Using immunohistochemistry, we have investigated the human retina and retinal pigment epithelium (RPE) for the presence and distribution of the so-called cardiac-type Na+/Ca2+ exchanger.

Paraffin sections of ten eyes enucleated for various disease processes were incubated according to the ABC method with a polyclonal antibody (pi) produced against the canine cardiac sarcolemmal Na+/Ca2+ exchanger. The reaction was visualized with aminoethylcarbazole.

There was a positive reaction with anti-Na+/Ca2+ exchanger in the retina and RPE in all eyes, but the labeling varied among the different specimens. In neural retina, staining was most intense in Mueller cells, in cells of the inner nuclear layer, and in cone inner segments. Immunoreactivity was less pronounced in ganglion cells, nerve fibers, the outer nuclear layer and in rod inner segments. Outer segments appeared mostly negative. In the RPE, positive staining was present but the intensity of staining varied both within and among the specimens. Reactive RPE cells revealed the most intense labeling.

Na+/Ca2+ exchanger of the cardiac type is present in human retina and RPE. The variation in immunoreactivity among the different specimens may reflect the different diseases of these eyes and their different metabolic states. A specific relation between certain diseases and malfunction of the Na+/Ca2+ exchanger could have a major impact on therapeutic regimens.