TABLE 2

Ternary complex model binding parameters for various allosteric modulators against [3H]NMS at human M2 mAChRs expressed in CHO cell membranes


Modulator

log KBa

Log αb

log(KB/α)c
Observedd
Calculatede
Gallamine −6.03 ± 0.02 −1.15 ± 0.08 (0.07) −4.54 ± 0.15 −4.88 ± 0.08
Alcuronium −5.92 ± 0.05 1.01 ± 0.10 (10.23) −6.61 ± 0.08 −6.93 ± 0.11
C7/3-phth
−6.75 ± 0.02
−0.98 ± 0.01 (0.10)
−5.56 ± 0.11
−5.75 ± 0.04
  • a Logarithm of the equilibrium dissociation constant for the allosteric modulator at the free receptor, determined from a nonequilibrium binding assay using nonlinear regression according to eqs. 6 through 9 under Materials and Methods. Values represent the mean ± standard error of the mean of six experiments conducted in triplicate.

  • b Logarithm of the cooperativity factor. Antilogarithm (geometric mean) is given in parentheses. All other details as in footnote a.

  • c Logarithm of the equilibrium dissociation constant for the allosteric modulator at the [3H]NMS-occupied receptor.

  • d Determined from dissociation kinetic experiments using nonlinear regression according to eq. 5 under Materials and Methods. The value of the slope factor, nH, was not significantly different from unity and was constrained as such, under which condition EC50 = KB/α. Values represent the mean ± standard error of the mean of three experiments conducted in duplicate.

  • e Calculated by dividing the dissociation constant of the modulator at the free receptor by the cooperativity factor determined for each individual nonequilibrium binding assay.