Ultrastructural studies on lysosomes in retinal Müller cells of streptozotocin-diabetic rats

Four Wistar inbred rats made diabetic by an injection of streptozotocin and four control rats were killed after an experimental period of 12 months. Eye tissues were prepared for examination and detection of acid phosphatase (AcPase) by electron microscopy. In the retina of control animals, the Müller cell cytoplasm had a small number of highly electron-dense bodies. AcPase reaction products were seen on these dense bodies and on Golgi lamellae of Müller cells. In the diabetic rat retina, a greater number of these lysosome-like bodies were seen, especially in cell processes adjacent to capillaries and in those at the vitreoretinal interface. Increased deposits of AcPase reaction products were detected on Golgi lamellae, smooth endoplasmic reticulum, and highly electron-dense bodies. The functional significance of a marked increase in lysosomal enzymes within Müller cells is uncertain. The phenomenon may occur in order to eliminate cellular debris derived from necrotic pericytes and to digest excessive glycogen accumulated in the retina under diabetic conditions.