Comparative study of a new ultrastructural specialization of the mammalian retinal pigment epithelium: Basal intracytoplasmic tubules

We recently described basal intracytoplasmic tubules that arise from the basal plasma membrane of rat retinal pigment epithelial cells (RPE). They are a previously undescribed ultrastructural specialization of the basal plasma membrane in addition to the well‐known basal folds. This report describes similar tubules in the RPE cells of the rabbit, hamster, and kitten. As in the rat, the tubules in the hamster and kitten ramify singly through the basal cytoplasm and bear no special relationship to any other organelle. In the rabbit, however, stacks of closely apposed tubules frequently abut the large lipid droplets in their RPE cells. Although the function of the tubules is unknown, their occurrence in several different mammals suggests they are involved in the function of RPE cells in general.