Insulin and Insulin Receptor Uptake into Rat Liver: Chloroquine Action on Receptor Recycling

In the present study, the effect of chloroquine on both insulin and receptor distribution was examined in vivo. Insulin injection (25 nmol/100 g body wt) caused a marked accumulation of both insulin and its receptor in purified hepatic Golgi fractions by 15 min postinjection. Percoll fractionation of parent Golgi fractions resolved two endocytic components of low (ρ = 1.040–1.050) and high (ρ = 1.053–1.064) density in which the relative distribution of insulin binding sites was unaltered by chloroquine. Chloroquine significantly accumulated in the high-density region of the Percoll gradient consistent with this being a low pH compartment. ¹²⁵I-insulin accumulated first in the low-density (1 min) and subsequently in the high-density region (5–10 min) of Percollsubfractionated Golgi fractions. Chloroquine treatment caused marked accumulation of ¹²⁵I-insulin in the highdensity compartment with substantial retention of radiolabel therein at 20 min postinjection. ¹²⁵I-insulin extracted from the Percoll fractions was comparably intact in control and chloroquine-treated rats. These data suggest that the chloroquine-accumulating, high-density compartment of hepatic Golgi fractions is the site of dissociation of internalized insulin-receptor complexes before degradation of the ligand and receptor recycling.