Endocytosis in absorptive cells of cultured human small-intestinal tissue: effect of cytochalasin B and D

The effect of cytochalasin B (CB) and cytochalasin D (CD) on the endocytotic uptake of horseradish peroxidase (HRP) by intestinal absorptive cells was investigated by morphometric methods. The results showed that CD inhibited endocytosis considerably, and without any detrimental side-effects. CB had hardly any effect on the endocytosis of HRP, but caused a significant decrease in the number of apical vesicles and tubules involved in the transport of cell-coat glycoproteins from the Golgi apparatus to the brush border. Electron-microscopic autoradiographic analysis of the effect of CD showed that although endocytosis is inhibited significantly by the drug, the amount of radiolabelled cell-coat material entering the lysosome-like bodies was unaltered compared with control cultures. These observations support our hypothesis that the cell-coat glycoproteins of the absorptive cells enter the lysosome-like bodies by a crinophagic rather than by an exocytotic-endocytotic mechanism.