Fig. 4. 5-HT is the only biogenic amine that acts as a potent agonist at 5-HT_2βPan and 5-HT_2βPro. (A) Non-transfected parental HEK cells do not show significant IP responses to any of the amines tested. (B) IP release in response to biogenic amines (10^–3 mol l^–1) in cells transiently expressing 5-HT_2βPan. Cells expressing 5-HT_2βPan demonstrate a greater than sixfold increase in IP release in response to 5-HT and a smaller but significant increase in response to dopamine and tyramine. Values are means ± s.e.m., N=3, ^**P<0.001 and ^*P<0.05 versus no drug control. (C) Dose–response curves of 5-HT_2βPan to biogenic amines in IP assay. 5-HT_2βPan responds to 5-HT (squares) with an EC₅₀ of 52 nmol l^–1. Dopamine (DA; circles) and tyramine (Tyr; triangles) activate the receptors only at very high concentrations. Non-transfected HEK cells do not respond to 5-HT (crosses). Values are means ± s.e.m., N=3. (D) IP release in response to biogenic amines (10^–3 mol l^–1) in cells transiently expressing 5-HT_2βPro. IP release is increased more than fourfold in response to 1 mmol l^–1 5-HT in cells expressing 5-HT_2βPro. A smaller but significant increase in response to dopamine is observed. Values are means ± s.e.m., N=3, ^**P<0.001 vs no drug control. (E) Dose–response curves of 5-HT_2βPro to biogenic amines in IP assay. 5-HT_2βPro responds to 5-HT (squares) with an EC₅₀ of 270 nmol l^–1. Dopamine (circles) activates the receptor only at very high concentrations. Non-transfected HEK cells do not respond to 5-HT (crosses). Values are means ± s.e.m., N=3.