Analgesic α-conotoxins modulate GIRK1/2 channels via GABA_Breceptor activation and reduce neuroexcitability

Abstract

Activation of G protein-coupled inwardly rectifying potassium (GIRK or Kir3) channels leads to membrane hyperpolarization and dampening of neuronal excitability. Here we show that the analgesic α-conotoxin Vc1.1 potentiates inwardly rectifying K+ currents (IKir) mediated through native and recombinant GIRK1/2 channels by activation of the G protein-coupled GABAB receptor (GABABR) via a Pertussis toxin (PTX)-sensitive G protein. Recombinant co-expression of human GIRK1/2 subunits and GABABR in HEK293T cells resulted in a Ba2+-sensitive IKir potentiated by baclofen and Vc1.1 which was inhibited by PTX, intracellular GDP-β-S, or the GABABR-selective antagonist CGP 55845. In adult mouse DRG neurons, GABABR-dependent GIRK channel potentiation by Vc1.1 and baclofen hyperpolarizes the cell resting membrane potential with concomitant reduction of excitability consistent with Vc1.1 and baclofen analgesic effects in vivo. This study provides new insight into Vc1.1 as an allosteric agonist for GABABR-mediated potentiation of GIRK channels and may aid in the development of novel non-opioid treatments for chronic pain.

ɑO‐Conotoxin GeXIVA isomers modulate N‐type calcium (CaV2.2) channels and inwardly‐rectifying potassium (GIRK) channels via GABAB receptor activation

“…Taken together, these data confirm that a significant portion of membrane excitability in DRGs is compensated by αO‐GeXIVA[1,3] which was inhibited by the GABA B R antagonist CGP 55845. These results are consistent with the decrease of membrane excitability by baclofen and α‐conotoxin Vc1.1 observed in mouse DRG neurons (Bony et al, 2021).…”

“…GAG, GG, G) were also tested on GABA B R‐coupled Cav2.2 channels in HEK293T cells. The present study shows that αO‐conotoxin GeXIVA inhibits native and recombinant GABA B R‐coupled Cav2.2 channels and potentiates GABA B R‐GIRK1/2 mediated inwardly rectifying K + currents which contribute to reducing excitability in mouse DRG neurons (Bony et al, 2021).…”

“…Interestingly, globular GeXIVA[1,3] also reversibly potentiated I Kir mediated by homomeric GIRK2 channels co‐expressed with GABA B R in HEK293T cells. α‐Conotoxin potentiation of GIRK‐mediated I Kir via GABA B R is a novel emerging field in pain modulation (Bony et al, 2021). The effects of αO‐GeXIVA on Cav2.2 and GIRK1/2 via GABA B R activation exhibit an approximately 10‐fold difference in potency between the signalling pathways similar to that reported previously for Vc1.1 and baclofen (Bony et al, 2021).…”

“…GFP(+ve) HEK293T cells and small to medium diameter (<30 µm) mouse DRG neurons were selected for whole‐cell patch‐clamp recording. As based on the previous studies of a similar nature (Bony et al, 2021), n ≥ 5 cells for each study. For GABA B R‐Cav2.2 measurements, all data points are plotted as % inhibition of baclofen‐sensitive current using the following equation:…”

“…Interestingly, GABA B Rs have also been reported to be activated by analgesic α‐conotoxins that antagonize α9α10 nAChRs (Berecki et al, 2014; Sadeghi et al, 2017, 2018). Inhibition of HVA calcium channels and potentiation of GIRK channel currents in DRG neurons by α‐conotoxins Vc1.1, RgIA, and PeIA attenuates neuronal excitability (Bony et al, 2021; Sadeghi et al, 2017).…”