Localization of alkaline phosphatase on basolateral plasma membrane of normal and regenerating retinal pigment epithelium. A cytochemical study in rabbits.

Ultrastructural cytochemistry was used to analyze the polarized distribution of alkaline phosphatase (AP) on the plasma membranes of normal and regenerating retinal pigment epithelium (RPE) and the ciliary body epithelium in rabbits. The AP activity was concentrated on the basolateral plasma membrane in normal RPE. In regenerating RPE (after intravenous administration of sodium iodate to damage the RPE), there was a differential expression of AP activity according to the site on the regenerating epithelial sheet. At the edge of the sheet, where cells were undifferentiated and immature (ie, without the polarized distribution of basolateral and apical plasma membrane specializations seen in normal RPE), no plasma membrane AP activity was observed. The AP activity was reexpressed more proximal in the regenerating sheet. It was first evident where contiguous cells formed junctional complexes and cytologic polarization again became apparent. New AP activity was restricted to the basolateral plasma membrane. Eventually, the polarized distribution of AP activity seen in normal RPE was reestablished. In the ciliary body, AP activity was localized to the basolateral plasma membranes of the outer, nonpigmented epithelial cells. It was concluded (1) that cytochemical activity for nonspecific AP is concentrated on the basolateral plasma membrane domain of normal RPE and the normal pattern of AP activity is lost initially and then reexpressed.