5-Hydroxytryptamine_1A receptor binding activity of bisbenzyltetrahydroisoquinoline alkaloids from Popowia odoardi

Figures & data

Figure 1.  (A) Saturation curve for the 5-hydroxytryptamine_1A receptor with [³H]8-OH-DPAT as the radioligand. Receptor membrane (35 μg protein/well) was incubated with increasing concentrations of [³H]8-OH-DPAT (0–10 nM) at 25°C for 90 min. The binding was fitted to the two-site binding model. The Rosenthal plot is shown as the inset of the saturation binding curve. (B) Time course of association of [³H]8-OH-DPAT to the 5-hydroxytryptamine_1A receptor. Receptor membrane (35 μg protein/well) was incubated with [³H]8-OH-DPAT (0.2 nM) at 25°C for different time periods (0–180 min). Each data point is expressed as mean ± SD (n = 3).

Figure 2.  Chemical structures of compounds isolated from P. odoardi as competitive inhibitors on [³H]8-OH-DPAT binding to 5-hydroxytryptamine_1A receptor.

Figure 3.  Competitive inhibition on the binding of [³H]8-OH-DPAT to the 5-hydroxytryptamine_1A receptor by O-methyldauricine and popisidine. Receptor membrane (35 μg protein/well) was incubated with [³H]8-OH-DPAT (0.4 nM) in the presence of O-methyldauricine and popisidine at 25°C for 90 min. Each data point is expressed as mean ± SD (n = 3).

Figure 4.  Chemical structures of asimilobine, nornuciferine and annonaine (aporphine alkaloids).

Table 1.  K_i values obtained from the competition experiments with standard unlabelled ligands on 5-HT_1A receptor binding activity with [³H]8-OH-DPAT as the radioligand.

Unlabelled ligand	Pharmacological action	Ki (M)
8-OH-DPAT	5-HT1A receptor agonist	0.2 × 10^−9, 1.34 × 10^−8 *
Buspirone	5-HT1A receptor agonist	1.46 × 10^−9, 2.69 × 10^−8 *
5-HT	5-HT receptor agonist	3.25 × 10^−9, 3.94 × 10^−6 *
Propanolol	5-HT1A receptor antagonist	1.37 × 10^−7 **

The values shown were the mean of three independent experiments; (±)-8-OH-DPAT = (±)-8-hydroxy-2-(di-n-propylamino)-tetralin; 5- HT = 5-hydroxytryptamine; *The data were fitted to a two-site competition curve giving inhibition constants for high-affinity (K_i(H)) and low affinity (K_i(L)) sites; **The data were fitted to a one-site competition curve.