TABLE 1

Equilibrium binding affinities

All data are presented as mean ± S.E.M. for n repeats, performed in duplicate.

Compound	α_1A-Adrenergic Receptor			α_1B-Adrenergic Receptor			α_1D-Adrenergic Receptor			5-HT_1A Receptor
Compound	pK_i	n	K_i (nM)	pK_i	n	K_i (nM)	pK_i	n	K_i (nM)	pK_i	n	K_i (nM)
Phentolamine	8.4 ± 0.06^{^c}	6	4	7.8 ± 0.2^{^c}	6	14	7.7 ± 0.06^{^c}	6	19	ND
Serotonin	ND			ND			ND			9.0 ± 0.06	6	1
9-aminoacridine	6.6 ± 0.03	3	250	5.6 ± 0.05	3	2600	5.7 ± 0.1	3	1900	<4
C2 bis(9-aminoacridine)	5.7 ± 0.1^{^c}	3	1900	6.6 ± 0.2^{^c}	3	250	5.9 ± 0.09	3	1400	<4
C3 bis(9-aminoacridine)	6.2 ± 0.09	3	700	6.4 ± 0.2^{^b}	3	430	5.9 ± 0.06	3	1200	4.8 ± 0.2	3	18,000
C4 bis(9-aminoacridine)	7.7 ± 0.2^{^c}	3	21	6.7 ± 0.1^{^c}	3	210	6.2 ± 0.03	3	650	5.5 ± 0.1	3	3000
C5 bis(9-aminoacridine)	7.5 ± 0.1^{^c}	3	33	7.0 ± 0.2^{^c}	3	94	6.4 ± 0.05^{^a}	3	360	5.8 ± 0.07	3	1800
C6 bis(9-aminoacridine)	7.2 ± 0.08	3	58	7.0 ± 0.1^{^c}	3	110	6.7 ± 0.07^{^c}	3	220	6.5 ± 0.05	3	340
C7 bis(9-aminoacridine)	6.9 ± 0.06	3	120	7.0 ± 0.2^{^c}	3	110	6.7 ± 0.09^{^c}	3	230	6.2 ± 0.09	3	620
C9 bis(9-aminoacridine)	6.6 ± 0.08	3	270	6.9 ± 0.2^{^c}	3	130	6.5 ± 0.1^{^a}	3	330	5.7 ± 0.2	3	1800
C10 bis(9-aminoacridine)	6.5 ± 0.07	3	290	6.8 ± 0.1^{^c}	3	150	6.4 ± 0.1^{^a}	3	370	6.0 ± 0.05	3	930
C12 bis(9-aminoacridine)	6.4 ± 0.2	3	400	6.9 ± 0.09^{^c}	3	120	5.8 ± 0.06	3	1600	6.0 ± 0.09	3	950
Tacrine	5.7 ± 0.06^{^c}	3	1900	4.7 ± 0.2^{^c}	3	19,000	5.2 ± 0.2	3	6400	ND

K_i, calculated concentration of ligand required to occupy 50% of unoccupied receptors, derived from pK_i; ND, not determined; pK_i, negative log of apparent affinity calculated according to the Cheng-Prusoff equation (Cheng and Prusoff, 1973).
↵^a P < 0.05 compared with 9-aminoacridine, not determined for 5-HT_1A receptor.
↵^b P < 0.01 compared with 9-aminoacridine, not determined for 5-HT_1A receptor.
↵^c P < 0.001 compared with 9-aminoacridine, not determined for 5-HT_1A receptor.