Retinal pigment epithelial cells of the posterior pole have fewer Na/K adenosine triphosphatase pumps than peripheral cells.

The density of Na/K adenosine triphosphatase (ATPase) pumps in retinal pigment epithelial (RPE) cells in different retinal regions was quantified by measuring the binding of 3H-ouabain to RPE in cow and human eyecups. In bovine eyes, pump density was estimated in RPE samples isolated from three retinal regions outlined with a 7-mm trephine: one from the posterior pole in the area centralis and two from the superior, equatorial retina representing unpigmented (in the tapetum) and pigmented zones. In human eyes, RPE samples were isolated from a posterior region centered around the macula and one superior region. Ouabain binding to RPE of the posterior pole of both species was approximately 40-60% lower than binding to RPE of more peripheral regions in the same eyes. For bovine eyes, ouabain binding did not differ between pigmented and unpigmented cells of the superior retina, suggesting that reduced binding in the relatively amelanotic posterior cells was not related to levels of pigmentation. For human RPE, binding to posterior cells was lower in eyes from donors of all ages (range, 17-90 yr). The data suggest that Na/K ATPase pump site density is lower in posterior RPE cells of both bovine and human eyes, perhaps due to a regional difference in requirements for ionic regulation.