Table 4

Effect of amiloride analogues on antagonist dissociation from the α_2A-adrenergic receptor

Antagonist	Amiloride analogue	n	k₋₁	k₋₂	Fold increase	logαK_X	logα_obs
			min⁻¹		k₋₂/k₋₁
Yohimbine		14	0.034 ± 0.001
	Amiloride	2	0.030 ± 0.001	0.060 ± 0.002	2.02 ± 0.01	2.12 ± 0.02	−2.40 ± 0.02
	DMA	3	0.035 ± 0.002	0.184 ± 0.005	5.3 ± 0.2	2.36 ± 0.03	−3.08 ± 0.03
	EPA^4-a	3	0.031 ± 0.001	4.8 ± 0.6	155 ± 22	1.75 ± 0.07	−4.02 ± 0.09
	MBA	2	0.032 ± 0.001	3.3 ± 0.1	101 ± 2	2.09 ± 0.03	−4.15 ± 0.03
	HMA	4	0.028 ± 0.003	3.7 ± 0.1	138 ± 15	2.47 ± 0.02	−4.21 ± 0.02
Rauwolscine		5	0.023 ± 0.001
	DMA	2	0.021 ± 0.001	0.135 ± 0.003	6.30 ± 0.05	2.27 ± 0.05	−3.17 ± 0.05
	HMA	3	0.025 ± 0.004	1.33 ± 0.03	57 ± 10	2.63 ± 0.03	−4.05 ± 0.03
RX821002		3	0.083 ± 0.002
	DMA	2	0.076 ± 0.001	0.54 ± 0.05	7.1 ± 0.8	2.07 ± 0.07	−3.37 ± 0.07

The experiments were performed at 20°, as described in the legend of Fig. 4. k₋₁ and k₋₂ are the dissociation constants for the dissociation of the antagonist from the unoccupied and the amiloride-occupied receptor, respectively (Fig. 1). The logα_obs is the difference between the log affinity of the amiloride analogue at the antagonist-occupied receptor (logαK_X) and the log affinity at the unoccupied receptor (logK_i, Table 3). Values are mean ± standard error of n experiments.

↵4-a The DPM from three experiments were converted to B_t/B_o; then, the combined data fitted. The error values quoted are the standard errors from the fit.