Table 2. M₂R Binding Characteristics of [³H]44 and [³H]64.

	saturation-binding	binding kinetics
radioligand	Kd [nM]a	Kd(kin) [nM]b	kon [min–1 nM–1]c	koff [min–1]d, t1/2 [min]d
[3H]44	1.0 ± 0.2	0.20 ± 0.03	0.078 ± 0.015	0.015 ± 0.001, 47 ± 3
[3H]64	0.081 ± 0.022	0.072 ± 0.002	0.31 ± 0.01	0.022 ± 0.002, 35 ± 1

^aDissociation constant determined by saturation binding at CHO-hM₂R cell homogenates; mean ± SEM from at least three independent experiments (performed in triplicate).

^bKinetically derived dissociation constant ± propagated error [K_d(kin) = k_off/k_on].

^cAssociation rate constant ± propagated error, calculated from k_obs (nonlinear regression), k_off (nonlinear regression), and the applied radioligand concentration (cf. Radioligand Binding).

^dDissociation rate constant (nonlinear regression, two ([³H]44)- or three ([³H]64)-parameter equation describing a monophasic decline) and half-life; mean ± SEM from three independent experiments (performed in triplicate).