Segmental distribution of epidermal growth factor binding sites in rabbit nephron

The kidney possesses epidermal growth factor (EGF) receptors and is a major site of synthesis for the EGF precursor, prepro-EGF. To examine the segmental localization of EGF receptors in the rabbit kidney, we characterized 125I-labeled EGF binding to micro-dissected rabbit nephron segments. Specific binding constituted 70-80% of total binding and was saturable with an apparent Kd of 8 nM. Kinetic studies (0 degrees C) revealed an association t1/2 of 20.7 min and a dissociation t1/2 of 27 min. Competition studies revealed that 125I-EGF binding was inhibited by unlabeled EGF or its homologue transforming growth factor-alpha, but not by parathyroid hormone or insulin. Mapping studies showed specific 125I-EGF binding (attomoles per centimeter) was highest in proximal straight tubules, followed by proximal convoluted tubules, cortical collecting ducts, inner medullary collecting ducts, outer medullary collecting ducts, and distal convoluted tubules. Specific binding to glomeruli was also observed. Interestingly, no specific binding of 125I-EGF to thick ascending limbs, a site of EGF precursor synthesis, was observed. These studies suggest potential sites of action for EGF in the rabbit kidney.