Table 1. Human AChR rate and equilibrium constants .

Site	Agonist	f1(s−1)	b1(s−1)	E1	kon(M−1s−1)	koff(s−1)	KdR (μM)	KdR* (nM)
α–ε	ACh	55.8	6,771	8.2 × 10−3	5.2 × 107	3,662	70.8	5.5
	CCh	32.0	7,884	4.05 × 10−3	1.7 × 107	2,236	182	21
	TMA	20.1	10,615	1.9 × 10−3	7.8 × 106	4,448	573	195
	Cho	2.12	12,325	1.72 × 10−4	2.04 × 106	5,884	2,884	10,867
α–δ	ACh	24.3	5,292	4.6 × 10−3	3.6 × 107	4,631	130	18.1
	CCh	10.4	6,830	1.5 × 10−3	8.1 × 106	3,345	413	176
	TMA	7.1	8,540	8.3 × 10−4	4.6 × 106	3,559	773	587
	Cho	1.1	12,950	8.5 × 10−5	1.6 × 106	7,601	4,750	34,697
α–δ	Epi	39.2	20,804	1.94 × 10−3	2.2 × 108	1,674	7.5	2.52
	Ebx	26.9	22,427	1.2 × 10−3	7.4 × 107	3,606	48.7	25.4
	Anx	6.72	23,150	2.9 × 10−4	3.7 × 107	4,273	115	247
	Aza	3.11	31,211	9.9 × 10−5	7.7 × 106	7,195	934	6,053
α–γ	ACh	377	6,658	5.6 × 10−2	2.9 × 108	4,020	13.8	0.02
	CCh	65.4	8,167	8.0 × 10−3	6.9 × 107	7,689	111	1.25
	TMA	23.5	12,071	1.9 × 10−3	2.7 × 107	8,696	322	14.9
	Cho	5.5	13,598	4.1 × 10−4	8.8 × 106	10,456	1,188	230

The active-state equilibrium constant was calculated from the activation thermodynamic cycle (Fig. 1 b) assuming microscopic reversibility, K_dR* = (K_dRE₀/E₁), where E₀ is the unliganded gating equilibrium constant and is equal to 6.6 × 10⁻⁷ (ΔG₀ = 8.4 kcal/mol) in adult-type and 8.6 × 10⁻⁸ (ΔG₀ = 9.6 kcal/mol) in fetal-type AChRs. f₁ and b₁, monoliganded forward and backward gating rate constants (E₁ = f₁/b₁); k_on and k_off, agonist association and dissociation rate constants to a resting receptor (K_dR = k_off/k_on).