Figure 3.

Affinities of the antagonist Bantag-1 for BB₂ receptor gain-of-affinity BB2 chimeric receptors and BB₃ receptor expressed in CHOP cells. The diagrams of the chimeric receptors formed are shown at the top. The chimeras BB₂ receptors were formed by replacing each of the extracellular domains of BB₂ receptor one at a time by the comparable BB₃* receptor extracellular domain as described in Material and Methods. The different concentrations of Bantag-1 were incubated with 50 pM ¹²⁵I- [D-Tyr⁶, β-Ala¹¹, Phe¹³, Nle¹⁴]Bn- (6–14) for 60 minutes at 21°C in 300 μl of binding buffer with (e1-BB₃) BB₂ cells (0.6 x 10⁶ cells/ml), (e2-BB₃) BB₂ cells (2 x 10⁶ cells/ml), (eC3-BB₃) BB₂ cells (1.4 x 10⁶ cells/ml) or BB₂ receptor cells (7.0 x 10⁶ cells/ml), and the saturable binding was determined as described under Materials and Methods. The results are expressed as the percentage of saturable binding without unlabeled peptide added (percentage control). The results are the mean and S.E.M. from at least three separate experiments and in each experiment the data points were determined in duplicated. The arrow indicates large change in affinity from the wild type BB₂ receptor. Abbreviations: see Fig. 1 legend.