Search

αO‐Conotoxin GeXIVA is a 28 amino acid peptide derived from the venom of the marine snail Conus generalis. The presence of four cysteine residues in the structure of GeXIVA allows it to have three different disulfide isomers, that is, the globular, ribbon or bead isomer. All three isomers are active at α9α10 nicotinic acetylcholine receptors, with the bead isomer, GeXIVA[1,2], being the most potent and exhibiting analgesic activity in animal models of neuropathic pain. The original report of GeXIVA activity failed to observe any effect of the isomers on high voltage‐activated (HVA) calcium channel currents in rat dorsal root ganglion (DRG) neurons. In this study, we report, for the first time, the activity of globular GeXIVA[1,3] at G protein‐coupled GABAB receptors (GABABR) inhibiting HVA N‐type calcium (Cav2.2) channels and reducing membrane excitability in mouse DRG neurons. The inhibition of HVA Ba2+ currents and neuroexcitability by GeXIVA[1,3] was partially reversed by the selective GABABR antagonist CGP 55845. In transfected HEK293T cells co‐expressing human GABABR1 and R2 subunits and Cav2.2 channels, both GeXIVA[1,3] and GeXIVA[1,4] inhibited depolarization‐activated Ba2+ currents mediated by Cav2.2 channels, whereas GeXIVA[1,2] had no effect. The effects of three cyclized GeXIVA[1,4] ribbon isomers were also tested, with cGeXIVA GAG being the most potent at human GABABR‐coupled Cav2.2 channels. Interestingly, globular GeXIVA[1,3] also reversibly potentiated inwardly‐rectifying K+ currents mediated by human GIRK1/2 channels co‐expressed with GABABR in HEK293T cells. This study highlights GABABR as a potentially important receptor target for the activity of αO‐conotoxin GeXIVA to mediate analgesia. [ABSTRACT FROM AUTHOR]

BACKGROUND AND PURPOSE Flupirtine is a non-opioid analgesic that has been in clinical use for more than 20 years. It is characterized as a selective neuronal potassium channel opener (SNEPCO). Nevertheless, its mechanisms of action remain controversial and are the purpose of this study. EXPERIMENTAL APPROACH Effects of flupirtine on native and recombinant voltage- and ligand-gated ion channels were explored in patch-clamp experiments using the following experimental systems: recombinant KIR3 and KV7 channels and α3β4 nicotinic acetylcholine receptors expressed in tsA 201 cells; native voltage-gated Na+, Ca2+, inward rectifier K+, KV7 K+, and TRPV1 channels, as well as GABAA, glycine, and ionotropic glutamate receptors expressed in rat dorsal root ganglion, dorsal horn and hippocampal neurons. KEY RESULTS Therapeutic flupirtine concentrations (≤10 µM) did not affect voltage-gated Na+ or Ca2+ channels, inward rectifier K+ channels, nicotinic acetylcholine receptors, glycine or ionotropic glutamate receptors. Flupirtine shifted the gating of KV7 K+ channels to more negative potentials and the gating of GABAA receptors to lower GABA concentrations. These latter effects were more pronounced in dorsal root ganglion and dorsal horn neurons than in hippocampal neurons. In dorsal root ganglion and dorsal horn neurons, the facilitatory effect of therapeutic flupirtine concentrations on KV7 channels and GABAA receptors was comparable, whereas in hippocampal neurons the effects on KV7 channels were more pronounced. CONCLUSIONS AND IMPLICATIONS These results indicate that flupirtine exerts its analgesic action by acting on both GABAA receptors and KV7 channels. [ABSTRACT FROM AUTHOR]

Pain severely affects the physical and mental health of patients. The need to develop nonopioid analgesic drugs to meet medical demands is urgent. In this study, we designed a truncated analogue of αO-conotoxin, named GeX-2, based on disulfide-bond deletion and sequence truncation. GeX-2 retained the potency of its parent peptide at the human α9α10 nAChR and exhibited potent inhibitory activity at Ca V 2.2 channels via activation of the GABA B receptor (GABA B R). Importantly, GeX-2 significantly alleviated pain in the rat model of chronic constriction injury. The dual inhibition of GeX-2 at both α9α10 nAChRs and Ca V 2.2 channels is speculated to synergistically mediate the potent analgesic effects. Results from site-directed mutagenesis assay and computational modeling suggest that GeX-2 preferentially interacts with the α10(+)α10(-) binding site of α9α10 nAChR and favorably binds to the top region of the GABA B R2 subunit. The study offers vital insights into the molecular action mechanism of GeX-2, demonstrating its potential as a novel nonopioid analgesic.