HIGH-RESOLUTION LOCALIZATION OF ENDOTHELIN RECEPTORS IN RAT RENAL MEDULLA

The cellular localization of endothelin receptors in the inner medulla of the rat kidney was investigated by using high resolution light and electron microscopic autoradiography, with the microwave irradiation fixation methods. Kidney slices were incubated with I-125-endothelin-1 alone or with selective ligands for the endothelin ET(B) and/or ET(A) receptors for light microscopic autoradiography. At the microscopic l evel, I-125-endothelin-1 was found to bind specifically to the glomeru li, arterioles and peritubular spaces in the cortex and vasa recta and surrounding tissues in the inner medulla. These bindings were also ob served when the tissue slices were incubated in the presence of IRL162 0 (ET(B) receptor agonist) or 97-139 (ET(A) receptor antagonist). Elec tron microscopic autoradiogra phy using I-125-endothelin-1 in the inne r medulla revealed silver grains over endothelial cells of the vasa re cta and interstitial and collecting duct cells. No grains were detecte d over inner lining cells of the thin limbs of Henle's loop. These int erstitial cells contained abundant microorganelles and lipid droplets, and had extensive cytoplasmic processes that closely related to the b asement membranes of the vasa recta and loop of Henle. These findings demonstrate that type 1 interstitial cells are also primary sites for endorhelin receptors as well as endothelial cells of the vasa recta an d collecting duct cells in the inner medulla.