Comparison of parameters describing M4 mAChR allosteric interactions analyzed with different allosteric models

M4 mAChR LY2033298 interactions with ACh in guanosine 5′-O-(3-[35S]thio)triphosphate binding assays were analyzed with the original operational model of agonism and allosterism (eq. 3) or the operational model of allosterism with cooperative agonist binding (eq. 4) to determine agonist or modulator affinity, agonist or modulator efficacy, cooperativity, transducer or binding slopes, and maximum system response. Values obtained from fitting eqs. 3 and 4 to the data were identical; therefore, they are only presented in a single column.

ParameterACh vs. LY2033298 (eqs. 3 and 4)a
pKA [KA (µM)]6.0 (1.0)b
pKB [KB (µM)]5.9 ± 0.3 (1.3)
Log τA (τA)0.9 ± 0.1 (7.9)
Log τB (τB)0.5 ± 0.2 (3.2)
Log αβ (αβ)0.7 ± 0.3 (5.0)
Em (% ACh maximum)112 ± 5.0
  • Dfd, degrees of freedom denominator; Dfn, degrees of freedom numerator; Em, maximum system response; Log αβ (αβ), cooperativity; Log τA (τA), agonist efficacy; Log τB (τA), modulator efficacy; n, transducer or binding slope; pKA (KA), agonist affinity; pKB (KB), modulator affinity.

  • a Data analyzed are from Leach et al. (2010).

  • b The pKA value was fixed to that determined in radioligand binding assays (Leach et al., 2010).

  • c An F test determined that data were fitted best when the transducer or binding slopes were not different from unity. The F data used to test the hypothesis that n differed from 1 were the following: eq. 3 P = 0.5766, F [(Dfn, Dfd) 0.3129 (1, 172)]; and eq. 4 P = 0.4541, F [(Dfn, Dfd) 0.5629 (1, 172)].