Characterization of beta-adrenergic receptors in DiFi and HT-29 cells

The beta-adrenergic receptors present in two human colorectal adenocarcinoma cell lines were characterized by measuring specific binding of [¹²⁵I]-cyanopindolol (CYP). Whole. cultured, DiFi (derived from a familial adenomatous polyposis [FAP] patient) and HT-29 cells were used in radioligand binding assays. Scatchard analysis of specific ¹²⁵I-CYP binding gave K(DS)of 38.6 ± 5.7 pM in DiFi cells and 54 ± 9.1 pM in HT-29 cells. However, binding site density (B(max)) in the DiFi cells was greater than that in HT-29 cell.s. In DiFi cells, the kinetically determined K(D) was similar to that calculated from Scatchard analysis. Studies in DiFi cells of the displacement of specific ¹²⁵I-CYP binding by nonselective (propranolol), beta₁-selective (metoprolol and atenolol), and beta₂-selective (ICI 118-551) antagonists revealed only a single class of beta₂-adrenergic receptors. This provides the first evidence that colorectal adenocarcinoma cell lines contain beta-adrenergic receptors and shows that only beta₂-adrenergic receptors are present in DiFi cells. Mechanisms possibly affecting beta-adrenergic-receptor expression in such cells are discussed in relation to colon carcinogenesis.