Uptake of pullulan in cultured rat liver parenchymal cells

Uptake of pullulan, including a binding process followed by internalization, was examined in cultured rat liver parenchymal cells. A tyramine derivative of pullulan was labeled with [I-125]iodine and used as a ligand. Pullulan bound to the cell surface was released by EDTA treatment, indicating that pullulan binding requires Ca2+ and a contribution from the asialoglycoprotein receptor. Binding of pullulan reached a steady state and internalization represented a biphasic mode, which included first- and zero-order processes in the initial stage and after 20 min incubation, respectively. The uptake of pullulan could be estimated by a similar model for intracellular disposition of asialofetuin. Kinetic parameters of pullulan constituting both binding and internalization were below those found for asialofetuin. These results suggest that pullulan is taken up by liver parenchymal cells via the asialoglycoprotein receptor; however, uptake availability is lower than that of asialofetuin.