THE SHAPE AND DISTRIBUTION OF LYSOSOMES AND ENDOCYTOSIS IN THE CILIARY EPITHELIAL-CELLS OF RATS

The shape and distribution of lysosomes in the ciliary epithelium of rat eyes were examined by electron microscopy combined with acid phosphatase (ACPase) cytochemistry and three-dimensional observation of 2 mum-thick sections. ACPase activity was cytochemically localized in lysosomes and trans Golgi cisternae in the non-pigmented epithelial (NPE) and pigmented epithelial (PE) cells. In NPE cells, it was shown three-dimensionally, that most lysosomes had an elongate form, up to 5 mum in length, and a diameter of 70-100 nm. These elongate lysosomes (nematolysosomes) were predominantly located in the basal region of the cells. In contrast, PE cells had spherical lysosomes distributed at random throughout the cytoplasm. However, no nematolysosomes were seen in the PE cells. When the isolated ciliary processes were incubated in a medium containing horseradish peroxidase (HRP), HRP was incorporated into the nematolysosome-like structures by pinocytosis from the basal surface of the NPE cells. These findings suggest that nematolysosomes are associated with the pinocytotic activity of NPE cells. The pinocytosis-nematolysosomal route may be involved in the uptake and degradation of macromolecules from the aqueous humor in the posterior chamber.