Bafilomycin A1, a specific inhibitor of vacuolar-type H+-ATPases, inhibits the receptor-mediated endocytosis of asialoglycoproteins in isolated rat hepatocytes

Background/Methods: The role of vacuolar type H+-ATPases (v-ATPases) and pH gradient between the endocytic compartments and cytoplasm in the endocytosis of asialoglycoproteins was morphologically investigated in isolated rat hepatocytes using bafilomycin A1, a specific inhibitor of v-ATPases. Results: Fluorescent staining by acridine orange showed that bafilomycin A1 inhibited the acidification of the endocytic compartments. Uptake of gold-conjugated asialofetuin was significantly inhibited by bafilomycin A1. However, bafilomycin A1 did not significantly inhibit uptake of a fluid phase marker, horseradish peroxidase. The number of autophagic vacuoles increased after the bafilomycin A1 treatment. However, materials in the autophagic vacuoles were rapidly degraded after the removal of bafilomycin A1. Conclusions: Results suggest that: (a) v-ATPases are necessary for acidification of the endocytic compartments; (b) the pH gradient between the endocytic compartments and the cytoplasm which is generated by v-ATPases is necessary for the receptor-mediated endocytosis of asialoglycoproteins, and (c) v-ATPases may contribute to the degradation of the materials in autophagic vacuoles.