title: Novel mechanism of voltage-gated N-type (Cav2.2) calcium channel inhibition revealed through α-conotoxin Vc1.1 activation of the GABA(B) receptor.
abstract: Neuronal voltage-gated N-type (Cav2.2) calcium channels are expressed throughout the nervous system and regulate neurotransmitter release and hence synaptic transmission. They are predominantly modulated via G protein-coupled receptor activated pathways, and the well characterized Gβγ subunits inhibit Cav2.2 currents. Analgesic α-conotoxin Vc1.1, a peptide from predatory marine cone snail venom, inhibits Cav2.2 channels by activating pertussis toxin-sensitive Gi/o proteins via the GABAB receptor (GABA(B)R) and potently suppresses pain in rat models. Using a heterologous GABA(B)R expression system, electrophysiology, and mutagenesis, we showed α-conotoxin Vc1.1 modulates Cav2.2 via a different pathway from that of the GABA(B)R agonists GABA and baclofen. In contrast to GABA and baclofen, Vc1.1 changes Cav2.2 channel kinetics by increasing the rate of activation and shifting its half-maximum inactivation to a more hyperpolarized potential. We then systematically truncated the GABA(B)(1a) C terminus and discovered that removing the proximal carboxyl terminus of the GABA(B)(1a) subunit significantly reduced Vc1.1 inhibition of Cav2.2 currents. We propose a novel mechanism by which Vc1.1 activates GABA(B)R and requires the GABA(B)(1a) proximal carboxyl terminus domain to inhibit Cav2.2 channels. These findings provide important insights into how GABA(B)Rs mediate Cav2.2 channel inhibition and alter nociceptive transmission.
authors.affiliation: Health Innovations Research Institute, RMIT University, Melbourne, Victoria, Australia (T.G.H., H.C., D.J.A.); and Peptide Biology Laboratories, The Salk Institute for Biological Studies, La Jolla, California (P.A.S.).
authors.forename: Thuan G
authors.initials: TG
authors.lastname: Huynh
authors.affiliation: Health Innovations Research Institute, RMIT University, Melbourne, Victoria, Australia (T.G.H., H.C., D.J.A.); and Peptide Biology Laboratories, The Salk Institute for Biological Studies, La Jolla, California (P.A.S.).
authors.forename: Hartmut
authors.initials: H
authors.lastname: Cuny
authors.affiliation: Health Innovations Research Institute, RMIT University, Melbourne, Victoria, Australia (T.G.H., H.C., D.J.A.); and Peptide Biology Laboratories, The Salk Institute for Biological Studies, La Jolla, California (P.A.S.).
authors.forename: Paul A
authors.initials: PA
authors.lastname: Slesinger
authors.affiliation: Health Innovations Research Institute, RMIT University, Melbourne, Victoria, Australia (T.G.H., H.C., D.J.A.); and Peptide Biology Laboratories, The Salk Institute for Biological Studies, La Jolla, California (P.A.S.).
authors.forename: David J
authors.identifier: http://orcid.org/0000-0002-7030-2288
authors.initials: DJ
authors.lastname: Adams
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism* / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000378:metabolism*; D020916:Conotoxins / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D017354:Point Mutation / Q000502:physiology; D051381:Rats; D018080:Receptors, GABA-B / Q000378:metabolism*
chemical_list: C503279:Cacna1b protein, rat; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D020916:Conotoxins; D018080:Receptors, GABA-B; C507383:alpha-conotoxin Vc1.1