Specific binding of calcitonin to rat liver plasma membranes.

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Abstract
The binding of human calcitonin (CT) [thyroid] was investigated in the plasma membrane fraction obtained from normal rat liver. The liver plasma membrane bound 125I-labeled ([125I]) human CT, with increasing concentrations of the plasma membrane protein from 4.6-80 .mu.g/ml, in a both time- and temperature-dependent manner. Specific binding of [125I] human CT was competitvely inhibited by concentrations of unlabeled homologous hormone more than 0.05 nM. Half-maximal inhibition of specific binding was observed with 0.5 nM human CT. Scatchard analysis of the data suggested the presence of 1 class of binding site with an apparent affinity constant of 4.08 .times. 109 M-1. The binding of human CT was highly specific; half-maximal inhibition of binding was observed with 100 nM synthetic (Asu1,7] eel CT; ACTH had no effect in this system. Specific binding receptor sites for CT are present in the plasma membrane of rat liver, compatible with the CT function in these cells.