Table 2

Agonist binding affinities of receptors formed by wild type and mutant neuronal nAChR subunits

Ligand	β2	N55S	V56I	T59K	E63T	T59D	β4
K _D, pM (n _H)
[³H]Epibatidine	4.7 ± 0.4	4.4 ± 0.3^2-170	7.8 ± 0.7^2-150 ^2-170	7.7 ± 0.4^2-160 ^2-170	6.0 ± 0.4^2-170	4.8 ± 0.7^2-170	50 ± 5^2-165
	(1.1 ± 0.2)	(1.0 ± 0.1)	(1.1 ± 0.1)	(1.0 ± 0.1)	(1.1 ± 0.1)	(1.0 ± 0.1)	(1.2 ± 0.1)
K _I, nM (n _H)
Acetylcholine	0.8 ± 0.2	2.6 ± 0.2^2-150 ^2-151	2.9 ± 0.2^2-150 ^2-151	6.1 ± 0.4^2-160 ^2-164	3.2 ± 0.1^2-160 ^2-151	3.5 ± 0.3^2-150 ^2-151	65 ± 12^2-150
	(0.7 ± 0.1)	(1.1 ± 0.1)	(1.1 ± 0.1)	(1.0 ± 0.1)	(1.0 ± 0.1)	(0.9 ± 0.1)	(0.6 ± 0.1)
Nicotine	0.37 ± .04	1.4 ± 0.1^2-150 ^2-164	1.5 ± 0.1^2-160 ^2-164	2.6 ± 0.2^2-160 ^2-170	1.4 ± 0.1^2-150 ^2-164	2.5 ± 0.2^2-160 ^2-164	43 ± 3^2-160
	(0.9 ± 0.1)	(1.1 ± 0.1)	(1.1 ± 0.1)	(1.1 ± 0.1)	(1.1 ± 0.1)	(1.0 ± 0.1)	(1.0 ± 0.1)
DMPP	4.6 ± 0.3	5.8 ± 0.8^2-164	6.9 ± 0.5^2-151	6.9 ± 0.7^2-151	8.1 ± 0.9^2-164	3.5 ± 0.2^2-151	735 ± 80^2-150
	(0.9 ± 0.1)	(1.0 ± 0.1)	(0.96 ± 0.06)	(0.9 ± 0.1)	(1.2 ± 0.1)	(1.0 ± 0.1)	(1.0 ± 0.1)

K_D values for [³H]epibatidine were taken from the fit data in Fig. 3. K_I values for acetylcholine, DMPP, and nicotine were calculated from the IC₅₀values determined in competition assays, as described underExperimental Procedures. All mutations are made in the β2 subunit. All β subunits are coexpressed with α2.

Statistically significant differences from β2 containing receptors:
↵2-150 p < 0.05,
↵2-160 p < 0.01,
↵2-165 p < 0.001. Statistically significant differences from β4 containing receptors:
↵2-151 p < 0.05,
↵2-164 p < 0.01,
↵2-170 p < 0.001.