Renal cortical endosomes participate in the degradation of insulin.

It has long been thought that metabolism of insulin by kidney proximal tubule cells takes place only in lysosomes. But previous studies with the perfused rat kidney and a proximal tubule-like cultured kidney cell line suggested that insulin degradation occurred in a nonlysosomal compartment. In this study we show that endosomes isolated from rat kidney cortex degrade insulin and that this process is ATP and pH dependent.