High resolution localization of angiotensin II receptors in rat renal medulla.

The cellular localization of angiotensin II (Ang II) receptors in the inner stripe of the outer medulla of the rat kidney was investigated by using high resolution light and electron microscopic autoradiography. Fresh tissue blocks from the inner stripe of the outer medulla were incubated with 125I-[Sar1, Ile8] Ang II and prepared for microscopic autoradiography. At the light microscopic level, 125I-[Sar1, Ile8] Ang II was found to penetrate into the tissue and to bind specifically to sites outlining renal tubules and vasa recta bundles. Electron microscopic autoradiography revealed that silver grains were detected over interstitial cells located between the tubules and components of the vasa recta bundles, but no silver grains were detected overlying the cells of the thin descending or thick ascending limbs of the loop of Henle, the collecting ducts, the vasa recta, or other blood vessels. These interstitial cells contained abundant endoplasmic reticulum, microfilaments, occasional lipid droplets and extensive cytoplasmic processes which closely related to the basement membranes of the vasa recta and loops of Henle. The cells therefore closely resemble type 1 interstitial cells. Since Ang II binding sites are absent in the inner medulla, the cells labelled by this technique must be a subset of type 1 interstitial cells, distinct from the typical lipid-laden interstitial cells most abundant in the inner medulla. These findings demonstrate that type 1 interstitial cells are the primary sites for a high density of Ang II receptors located in the inner stripe of the outer medulla.