TABLE 3

Quantification of Embedded Image affinity and efficacy for CaSR-Ca2+i mobilization using the operational model of agonism

Embedded Image concentration-response curves were generated at the WT receptor following overnight incubation of cells with or without 100 ng/ml tetracycline to induce receptor expression. For N-terminally truncated CaSRs, Embedded Image and Embedded Image concentration-response curves were generated upon induction of expression with 100 ng/ml tetracycline, where Embedded Image is a partial agonist and Embedded Image is a full agonist. The Black-Leff model (eq. 1) or the cooperative agonist operational model (eq. 2) was fitted to data to determine agonist affinity, efficacy, and transducer or binding slope.

ParameterWTN-terminally truncated CaSR
eq. 1eq. 2eq. 1eq. 2
pKA [KA (mM)]3.7 ± 0.3 (0.2)3.0 ± 0.1 (1.0)2.3 ± 0.2 (5.0)2.3 ± 0.2 (5.0)
Log τA (τA)100 ng/ml tet: 0.2 ± 0.1 (1.6) 0 tet: −0.01 ± 0.01 (1.0)100 ng/ml tet: 1.2 ± 0.2 (16) 0 tet: −0.1 ± 0.1 (0.8)0.2 ± 0.1 (1.6)0.2 ± 0.1 (1.6)
n6.0 ± 3.0a2.0 ± 0.3a1.0b1.0b
  • Dfd, degrees of freedom denominator; Dfn, degrees of freedom numerator; Log τA (τA), efficacy; n, transducer or binding slope; pKA (KA), agonist affinity; tet, tetracycline.

  • a An F test determined that data were fitted best when the binding or transducer slopes were different from unity. The F data used to test the hypothesis that n differed from 1 were the following: eq. 1 P < 0.0001, F [(Dfn, Dfd) 48.57 (1, 74)]; and eq. 2 P < 0.0001, F [(Dfn, Dfd) 45.78 (1, 74)].

  • b An F test determined that data were fitted best when the binding or transducer slopes were not different from unity. The F data used to test the hypothesis that n differed from 1 were the following: eq. 1 P < 0.2282, F [(Dfn, Dfd) 1.470 (1, 101)]; and eq. 2 P < 0.5332, F [(Dfn, Dfd) 0.3910 (1, 101)].