TABLE 3 The ratio of the log KB value for CGP12177 (as an antagonist of cimaterol; thus, at the high-affinity conformation) and log EC50 value for CGP12177 (as an agonist of the secondary low-affinity conformation) for responses seen at the β1-WT and β1-TM chimeric receptors (data taken from Table 2)
The ratios of the affinity for antagonists at the two conformations (i.e., log KB for antagonism of cimaterol at high-affinity site/log KB for antagonism of CGP12177 at low-affinity site) were determined. This table examines the ratio of the affinities of ligands at the two conformations of the β1-adrenoceptor and thus allows for differences in absolute affinity. For example, ICI118551 has a higher affinity at the β1-TM7 receptor (Table 2) than the β1-WT receptor; however, the ratio of the affinity in the presence of cimaterol and CGP 12177 is similar to that at the WT receptor, suggesting that although the β1-TM7 mutation alters the affinity of ICI118551, it does not alter the secondary conformation. The most consistent change is seen with the β1-TM4 mutation, where the ratios are all nearly 0, suggesting no difference in affinity (i.e., no secondary conformation).