Cellular distribution of 125I-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 lines by radioreceptor assay, but the precise cellular localization of these receptors under in vivo conditions remains to be determined. We performed electron microscopic autoradiography on rat kidney following intravenous administration of 125I-labeled ET-1. In vivo autoradiographs revealed binding patterns identical to those previously demonstrated following in vitro labeling. Light microscopic autoradiography showed that silver grains occurred exclusively overlaying glomeruli and peritubular capillaries in the cortex, inner stripe of the outer medulla, and the inner medulla. At the electron microscopic level, ET-1 binding was specifically localized to the fenestrated endothelium of glomerular and peritubular capillaries, and to a lesser extent to the vasa recta. No significant grains were seen on mesangial or visceral epithelial cells; nor were any seen on the cells of proximal tubule, the thick and thin limbs of the loop of Henle, the medullary collecting ducts, and renal interstitial cells. These results indicate that the endothelial cells of glomerular and peritubular capillaries are the primary target for the circulating ET-1 in the rat kidney and suggest an autocrine and/or paracrine function of locally synthesized ET-1 in vivo in both physiological and pathophysiological states.