CELLULAR-DISTRIBUTION OF I-125 ENDOTHELIN-1 BINDING IN RAT-KIDNEY FOLLOWING IN-VIVO LABELING

Endothelin-1 (ET-1) receptors have previously been demonstrated in the rat kidney by in vitro autoradiography and in cultured renal cell lin es by radioreceptor assay, but the precise cellular localization of th ese receptors under in vivo conditions remains to be deter mined. We p erformed electron microscopic autoradiography on rat kidney following intravenous administration of I-125-labeled ET-1. In vivo autoradiogra phs revealed binding pat terns identical to those previously demonstra ted following in vitro labeling. Light microscopic autoradiography sho wed that silver grains occurred exclusively overlaying glomeruli and p eritubular capillaries in the cortex, inner stripe of the outer medull a, and the inner medulla. At the electron microscopic level, ET-1 bind ing was specifically localized to the fenestrated endothelium of glome rular and peritubular capillaries, and to a lesser extent to the vasa recta. No significant grains were seen on mesangial or visceral epithe lial cells; nor were any seen on the cells of proximal tubule, the thi ck and thin limbs of the loop of Henle, the medullary collecting ducts , and renal interstitial cells. These results indicate that the endoth elial cells of glomerular and peritubular capillaries are the primary target for the circulating ET-1 in the rat kidney and suggest an autoc rine and/or paracrine function of locally synthesized ET-1 in vivo in both physiological and pathophysiological states.