Estradiol-binding sites in rat aortic smooth muscle cells in culture

To determine whether aortic smooth muscle cells possess estradiol receptors or not, an estradiol binding study has been performed in cultured rat aortic smooth muscle cells by using an intact-cell assay. Specific binding for estradiol is shown by the cells, and the binding reaches a plateau after 15 min of incubation at 37°C. The binding curve shows a saturable binding process. Scatchard analysis reveals a single population for estradiol binding with a dissociation constant of 5.0 X 10^-8 M and specific binding sites of 64 fmole per 10⁶ cells (38,500 sites per cell). Molecular specificity shows highly specific binding with estradiol. Among various steroids tested, only testosterone at 10^-5 M competes slightly (9.3%) with the estradiol-specific binding. These data indicate the existence of specific, high-affinity and limited-capacity binding sites for estradiol in rat aortic smooth muscle cells. This accords with the concept that estrogen responsiveness in aortic smooth muscle cells is mediated through the estrogen-receptor binding in the cells.