Insulin processing by cultured hepatocytes.

The chloroquine-sensitive and chloroquine-insensitive steps in insulin degradation by cultured hepatocytes have been explored by employing low temperature to retard processing. Under standard conditions (90 min association and 60 min dissociation) chloroquine inhibited insulin degradation at 15 degrees C but not at 37 degrees C. However, if the association and dissociation periods were short so that only early degradation was examined, marked inhibition of insulin degradation by chloroquine could also be observed at 37 degrees C. This inhibitory effect was observed only during the first 15 min, being masked by increased insulin degradation subsequently. An increase in slowly dissociable insulin, as well as a twofold increase in volume density of multivesicular bodies (MVB), occurred in the presence of chloroquine at both 37 and 15 degrees C. Rapid insulin processing from the slowly dissociable compartment at 37 degrees C masked chloroquine's effect on insulin processing under usual conditions at that temperature. At physiological temperature the chloroquine-sensitive step is not obligatory for insulin degradation by hepatocytes.