Inhibition of Pinocytosis by Cytochalasin B

The influence of Cytochalasin B on the pinocytosis of lysosomal enzymes and on the intracellular accumulation, secretion and uptake of sulfated glycosaminoglycans has been studied in cultivated skin fibroblasts. The uptake of α‐ N ‐acetylglucosaminidase was measured in Sanfilippo B fibroblasts, that of β‐ N ‐acetylhexosaminidase in Sandhoff fibroblasts and that of β‐glucuronidase in fibroblasts from a patient with β‐glucuronidase deficiency. Cytochalasin B reduces drastically the uptake of these glycosidases. For α‐ N ‐acetylglucosaminidase a dose‐response relationship and the time interval between application of the drug and the onset of inhibition of pinocytosis are given. When normal fibroblasts are incubated in the presence of Cytochalasin B the cells become depleted of the intracellular activity of lysosomal hydrolases but not of the cytoplasmic enzyme lactate dehydrogenase. In the medium an increase of β‐ N ‐acetylhexosaminidase activity is measurable. The decrease of the activity of intralysosomal enzymes mirrors their intracellular half‐life time as determined in mutant cell strains. As a consequence of the lowered hydrolase activity excesive amounts of sulfated glycosaminoglycans are accumulated in normal fibroblasts although the pinocytosis of secreted proteoglycans is markedly diminished. The results support the hypothesis that in fibroblasts lysosomal enzymes are primarily secreted and reach thereafter the lysosomes by adsorptive pinocytosis.