Internalization of large macromolecules in human Chang liver cells by extracellular ATP

The home of all intermediary metabolism and the cytoskeleton, viz. the cytosol, appears inaccessible to large macromolecules in the living state without severe perturbations. ATP-induced cytosolic penetration due to poration which allow passage of < 1000 mol. wt. particles have been cited. We report here that at similar milli-molar dosage levels of ATP, internalization of 2,000,000 mol. wt dextran particles as well as 0.92 micron and 2.17 microns latex beads could be demonstrated. At ultrastructural level, the internalized beads were seen distributed in 2 sites on the cytoplasm of the cell, viz. (a) inside vacuoles and (b) outside vacuoles, in the cytosol. The vacuolar distribution suggests endocytic entry, while the cytosolic distribution suggests a cellular sorting process where the boundary of the bead is processed or sorted out of the membrane-recycling pathway.