Changes in distribution of chloride ions in embryonic chicken retinal pigment epithelium

Changes in the distribution pattern of chloride ions were studied in the embryonic chicken retinal pigment epithelium (RPE), chloride ions being deposited as silver chloride (AgCl) in the RPE and observed by electron microscope. Before the 7th day after fertilization, the chloride ions did not accumulate anywhere in the tissue. From the 8th day, the chloride ions accumulated in the cytoplasm and the intercellular space, first in the posterior fundus RPE and later in the anterior fundus RPE. Melanin pigment granules and apical microvilli of the RPE developed from the posterior fundus toward the anterior fundus in parallel with the changes in the distribution pattern of chloride ions. These results suggest that the chloride ion transport function of the RPE appears first in the posterior fundus on the 8th day after fertilization and thereafter the development of the chloride ion transport moves to the anterior fundus. This development of the transport function appears to progress in parallel with the morphological development of the RPE cells.