IGF-I receptor binding, autophosphorylation, and kinase activity in kidney and muscle of acutely uremic rats.

Following acute tubular necrosis (ATN), kidney plasma membrane insulin-like growth factor-I (IGF-I) receptor number increases markedly, although IGF-I receptor mRNA levels do not change. To determine whether this increase could represent a redistribution of intracellular receptors and whether receptor function is intact in acute uremia, rats with ATN of 2 days duration and pair-fed controls were studied. Skeletal muscle receptor binding was unchanged. In contrast, binding to receptors in solubilized cortex and isolated cortical plasma membranes increased significantly due to an increase in receptor number. However, the increase in membrane binding was threefold greater than the increase in solubilized cortex binding. This indicates that the increase in total cellular IGF-I receptors can only account for a minor portion of the increase in abundance of plasma membrane receptors number and is consistent with a redistribution of receptors from an intracellular to a membrane location as the major mechanism. Autophosphorylation and receptor kinase activity were unaffected by the uremia (blood urea nitrogen of approximately 198 mg/dl). Since these early steps of IGF-I receptor signaling are intact early in acute uremia, it is likely that at this time in the course of the disease the increase in receptor number will heighten the sensitivity to IGF-I and may thus favor its participation in renal repair.