ULTRASTRUCTURAL IMMUNOGOLD LOCALIZATION OF OSTEOPONTIN IN HUMAN GALLBLADDER EPITHELIAL-CELLS

We used a post-embedding ultrastructural immunogold method to localize osteopontin in human gallbladder epithelial cells. This glycoprotein, originally described in bone but recently found to have a much wider distribution in many epithelia and in some mesenchymal cells, was pres ent in the filamentous glycocalyx, small apical cytoplasmic smooth mem brane-bound vesicles, large membrane-bound cytoplasmic granules, and i n portions of the Golgi complex in gallbladder columnar epithelial ail s. These findings suggest that newly synthesized osteopontin is packag ed in Golgi-derived granules that release their contents by classical exocytosis from the cell surface. At least a portion of secreted osteo pontin remains on the cell surface, where it becomes integrated into t he filamentous glycocalyx coating the luminal surface of gallbladder e pithelial cells.