LOCALIZATION OF EPIDERMAL GROWTH-FACTOR (EGF) BINDING-SITES ON ANTILUMINAL PLASMA-MEMBRANE OF RAT-KIDNEY - AUTORADIOGRAPHIC STUDY USING NONFILTERING PERFUSED RAT-KIDNEY

We previously demonstrated that the specific binding of EGF to the antiluminal plasma membrane was a prerequisite step for the renal uptake of EGF. In the present study, the localization of I-125-EGF binding sites on the antiluminal plasma membrane was investigated by tissue sampling and X-ray autoradiography in the nonfiltering kidney. The binding of I-125-EGF was recognized over the whole kidney and was highest in the inner medulla followed by the cortex and outer medulla. The binding of I-125-EGF in the nonfiltering kidney was completely inhibited in the presence of 20 nM unlabeled EGF, suggesting specific binding of I-125-EGF to its receptor. Further, we used a histologic tissue staining method to confirm the location of the I-125-EGF binding sites. Binding of I-125-EGF was demonstrated on the proximal straight tubules (PST), cortical collecting ducts (CCD), inner medullary collecting ducts (IMCD), and thin limb of Henle in the inner medulla (IMTLH). We found that the binding of I-125-EGF was high in the IMTLH. In addition, we determined the grain density both on the cell surface membrane and in the intracellular space of the proximal straight tubules, where the grain density on the antiluminal plasma membrane was approximately 50% that in the intracellular space at 20 min after the start I-125-EGF perfusion, suggesting the internalization of I-125-EGF from the antiluminal plasma membrane to the intracellular compartment. In conclusion, the binding sites of I-125-EGF, which were accessible from the antiluminal side, were broadly distributed over the whole kidney and were most dense around the IMTLH.