Figure 2.

Analgesic α‐Ctxs Vc1.1, RgIA and RgIA4 fail to activate heterologously expressed GABA_B receptors. α‐Ctxs have not shown agonist activity in a variety of functional assays designed to measure GABA_B receptor activity. (A) Vc1.1 failed to activate human GABA_B receptors functionally coupled to K_ir (GIRK) channels expressed in Xenopus oocytes. The oocytes were stimulated with 45 mM K⁺ and then pulsed with GABA or GABA + Vc1.1 to stimulate GABA_B receptor activation of K_ir channels. Note that GABA, but not Vc1.1, increased K⁺ currents. Similar results were obtained with RgIA in the same assay. (B) Histogram showing the lack of effect of Vc1.1 and RgIA on K_ir channel activation. (figures in A and B were used with permission of McIntosh et al., 2009). (C) G_i‐coupled cAMP modulation was assessed in CHO cells expressing GABA_B1a/B2 receptors with G_i/o coupling. GABA produced an increase in cAMP response in a concentration‐dependent manner, whereas RgIA4 had no effect at any of the concentrations tested. (D) Cellular dielectric spectroscopy was used to assay changes in electrical impedance using CHO cells expressing human GABA_B1a/B2 receptors during stimulation with the GABA_B receptor agonist 3‐aminopropyl(methyl)phosphonic acid (3‐AMPA). 3‐AMPA produced changes in cellular impedance in a concentration‐dependent manner, whereas RgIA4 had no effect. (Figures in C and D were used with the permission of Romero et al., 2017).