ULTRASTRUCTURAL STUDY OF ENDOCYTOSIS IN PRINCIPAL CELLS OF THE CASTRATED RAT EPIDIDYMIS

Abstract

To trace the pathways of endocytotic vesicles from the luminal surface membranes of the principal cells of the caudal epididymis, horseradish peroxidase (HRP) (M. W. 40, 000) and dextran (M. W, 40.000) were infused into the epididymal lumen of normal and castrated rats. Attention was focused on the dynamic morphology of the Golgi apparatus and two kinds of vesicles of different sizes: large (100-150nm in diameter) and small (less than 50nm in diameter) ones. In principal cells of normal rat epididymis, both HRP and dextran were taken up into large vesicles and then into lysosomes 5-120min after infusion. In these cells of castrated rat epididymis, druing the period from 5 to 60min after infusion, HRP and dextran were first taken up into large vesicles and then into lysosomes and/or the Golgi cisternae and the tracers were absent in small vesicles originated from the Golgi cisternae. Some of the small vesicles containing the tracers, however, were certainly found in areas close to the Golgi cisternae, lysosomes and to the surface membranes 120-180min after infusion. These findings suggest that luminal surface membranes in castrated state are interalized by endocytosis and then fused with the Golgi cisternae in the form of large vesicles, and that small vesicles formed subsequently by pinching off from the Golgi cisternae are in part transported at least to the luminal surface membranes.