Localization of glucose-6-phosphatase activity and carbohydrates in boar caput epididymal principal cells

Unidentified tubulovesicular profiles have been reported in the apical cytoplasm of boar caput epididymal principal cells in addition to vesicles considered to be involved in endocytosis and secretion. The main aim of the present study was to clarify the character of these organelles and to differentiate them from the endocytic apparatus. Glucose-6-phosphatase (G6Pase) activity was determined as the reporter enzyme of the endoplasmic reticulum (ER) and phosphotungstic acid was used to visualize carbohydrate moieties in both the proximal and distal caput. Phosphotungstic acid revealed the glycocalyx of the endocytic apparatus, which was similar in both regions studied, and also stained specific granules of the proximal caput. Glucose-6-phosphatase showed the tubulovesicular profiles to be sparsely granulated ER that was poorly developed in the proximal caput and very abundant in the apical cytoplasm of the distal caput principal cells. The function of such large amounts of sparsely granulated ER with corresponding G6Pase activity in caput epididymal principal cells is unknown.