Binding of IGF I and IGF I-stimulated phosphorylation in canine renal basolateral membranes.

To characterize the interaction of the renal proximal tubular cell with insulin like growth factor I (IGF I), we measured binding of 125I-IGF I to proximal tubular basolateral membranes from dog kidney and induced IGF I-stimulated phosphorylation of basolateral membranes. Specific binding of 125I-IGF I to basolateral membranes was observed that was half-maximal at between 10(-9) and 10(-8) M IGF I. 125I-IGF I was affinity cross-linked to a 135,000 Mr protein in basolateral membranes that was distinct from the alpha-subunit of the insulin receptor and from the IGF II receptor. IGF I-stimulated phosphorylation of a 92,000 Mr protein was effected in detergent-solubilized membranes incubated with 100 microM [gamma-32P]ATP. The 32P-labeled protein was distinct from the beta-subunit of the insulin receptor, the 32P phosphorylation of which was stimulated by insulin. We conclude that specific receptors for IGF I are present in the basolateral membrane of the renal proximal tubular cell. Physiological actions of IGF I at this nephron site may occur through the binding of this peptide circulating in plasma, to specific basolateral membrane receptors, followed by IGF I stimulated phosphorylation.