The liver parenchymal cells of rainbow trout (Salmo gairdneri) endocytose mannose-terminated glycoproteins

A mannose-terminated glycoprotein,¹²⁵I-invertase, was taken up and degraded by isolated rainbow trout liver cells at 12°C. The uptake was inhibited by EGTA and no degradation occurred in the presence of ammonium ions. The liver cell suspension was fractionated by differential centrifugation in parenchymal and nonparenchymal cells, respectively. The parenchymal liver cells seemed to be the most active cells in uptake of labelled invertase bothin vitro andin vivo. Only negligible amounts of ligand were recovered in the nonparenchymal cells. Internalization of¹²⁵I-invertase at different temperatures was demonstrated indirectly by releasing surface-bound ligand with EGTA. Ligand was internalized even at 0°C in trout liver cells.In vitro uptake of¹²⁵I-invertase was inhibited by excess unlabelled invertase, by mannan and by N-acetylglucosamine.These data suggest that invertase is endocytosed by a mannose-specific pathway by the parenchymal liver cells of rainbow trout.