Characterization and quantitative topographical distribution of salmon calcitonin‐binding sites in rat kidney sections

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Abstract
Renal binding sites for labelled salmon calcitonin (sCT) were studied using cryostat sections and autoradiography. Increasing concentrations of unlabelled sCT inhibited 125I‐sCT binding. 125I‐sCT bound to a single site with a K d of 2 nM and a number of sites of 220 protein. Mammalian calcitonins had low affinities and peptides unrelated to CT were devoid of any significant affinity for 125I‐sCT receptors. Auto‐radiograms disclosed a high concentration of 125I‐sCT receptors mainly located in the outer medulla and heterogeneously in the renal cortex. The distribution of specific binding sites is in agreement with the current concepts of renal action of calcitonin.