IMMUNOCYTOCHEMICAL ANALYSES OF DISTRIBUTIONS OF NA, K-ATPASE AND GLUT1, INSULIN AND TRANSFERRIN RECEPTORS IN THE DEVELOPING RETINAL-PIGMENTEPITHELIAL-CELLS

The retinal pigment epithelium (RPE) is unique in that Na, K-ATPase is predominantly localized on its apical surface. We studied the distrib utions of Na, K-ATPase and glucose transporter GLUT1, insulin and tran sferrin receptors in developing rat RPE cells immunocytochemically. Na , IC-ATPase, first detected in Id-day-old embryonic eyes, was already distributed predominantly on the apical surface. This reversed distrib ution of Na, K-ATPase was maintained throughout their life. Insulin re ceptor and transferrin receptor were distributed exclusively on the ba solateral surface. By quantitative immunogold electron microscopic tec hnique we found that glucose transporter GLUT1 is distributed almost e qual in amount on both the apical and basolateral surfaces of RPE cell s, thus presumably constructing an efficient pathway for glucose trans port from the choriocapillaries to the neural retina through the blood -retinal barrier. These results suggest that in the RPE cells the intr insic basolateral plasma membrane proteins are sorted out at least in three different ways.