Binding of insulin-like growth factor-I by glomerular endothelial and epithelial cells: Further evidence for IGF-I action in the renal glomerulus

The renal glomerulus is both a site of action and synthesis of IGF-I. We previously demonstrated the presence of IGF-I receptor and synthesis in glomerular mesangial cells. In this study we investigated the presence of specific IGF-I receptors on mouse glomerular endothelial and epithelial cells in culture. [¹²⁵I]IGF-I specifically bound to the cell surface of both cell types. Maximum specific binding, 0.141 B F for endothelial cells and 0.301 B F for epithelial cells, was obtained at 22°C after 150 min incubation. The estimated K_d values were 2.25×10^-9 for endothelial cells and 1.5×10^-9 for epithelial cells. Cross-linking studies showed a single band of radioactivity with an estimated mol wt of 145K, consistent with the α-subunit of the IGF-I receptor. Radiolabelled IGF-I was not degraded by either cell types. These findings suggest a possible paracrine action of IGF-I in the renal glomerulus.