Localization of binding sites for alpha-rat atrial natriuretic polypeptide in rat kidney

To determine the intrarenal localization of receptors for atrial natriuretic polypeptide (ANP) in the rat, we performed autoradiography and binding assay by using 125I-labeled alpha-rat ANP (alpha-rANP). Autoradiography at the slice and microscopic level in the kidney and binding assay in isolated glomeruli demonstrated that receptors in the renal cortex were distributed mainly in glomeruli. Although dense silver grains were distributed diffusely both in inner medulla and outer stripe of outer medulla, a marked displacement of the grains was observed only in the inner medulla. Autoradiography at the microscopic level also showed that silver grains were distributed in the renal artery, renal pelvis, and inner medullary collecting tubule (IMCT) prepared by the microdissection method, but not in the arcuate artery, interlobular artery, and afferent or efferent arterioles. Specific binding was demonstrated in the isolated glomeruli and the preparation was rich in fragments of IMCT. Apparent binding affinity (Kd) and receptor density (R) for 125I-labeled alpha-rANP in isolated glomeruli and IMCT were Kd = 3.2 and 21 X 10(-9) M, and R = 320 and 420 fmol/mg protein, respectively. These observations suggest that alpha-rANP has a physiological action on glomeruli and possibly on the inner medullary collecting tubules in addition to the renal artery.