title: Analgesic α-conotoxins Vc1.1 and RgIA inhibit N-type calcium channels in sensory neurons of α9 nicotinic receptor knockout mice.
abstract: Alpha-conotoxins Vc1.1 and RgIA are peptides from the venom of marine Conus snails that are currently in development as a treatment for neuropathic pain. We have reported previously that the alpha9alpha10 nicotinic acetylcholine receptor (nAChR) selective-conotoxins Vc1.1 and RgIA potently and selectively inhibit high voltage-activated (HVA) N-type calcium channel currents in dissociated neurons from rat dorsal root ganglia (DRG). Our data indicated that Vc1.1 does not interact directly with N-type Ca(2+) channels but inhibits them via GABA(B) receptor activation. The present study investigated Vc1.1 and RgIA inhibition of N-type Ca(2+) channels currents in DRG neurons of wild-type and alpha9 knockout (KO) mice to determine if the alpha9 nAChR was necessary for inhibition of the Ca(2+) channel current. Application of Vc1.1 (100 nM) inhibited N-type Ca(2+) channel currents to 69.2 +/- 3.5% of control in DRG neurons isolated from wild-type mice. In >70% of DRG neurons isolated from the alpha9 KO mice, both Vc1.1 and RgIA selectively inhibited N-type Ca(2+) channel currents with an IC(50) of 24.6 nM and 22.4 nM, respectively. The GABA(B) receptor antagonist CGP55845 (1 microM) antagonized the effect of Vc1.1 and RgIA on the N-type calcium channels in alpha9 KO mice. RT-PCR and western blot analysis confirmed the absence of the alpha9 nAChR in mice carrying a null mutation for the nAChR alpha9 gene. These results demonstrate that the inhibition of N-type Ca(2+) channel channels by Vc1.1 and RgIA is not mediated by the expression of alpha9alpha10 nAChRs in DRG neurons.
authors.affiliation: Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.
authors.forename: Brid
authors.initials: B
authors.lastname: Callaghan
authors.forename: David J
authors.initials: DJ
authors.lastname: Adams
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000187:drug effects*; D020916:Conotoxins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists / Q000494:pharmacology; D058788:GABA-B Receptor Antagonists; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D010721:Phosphinic Acids / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D018080:Receptors, GABA-B / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000172:deficiency* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D000700:Analgesics; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; C402445:Chrna9 protein, mouse; D020916:Conotoxins; D018756:GABA Antagonists; D058788:GABA-B Receptor Antagonists; D010721:Phosphinic Acids; D011412:Propanolamines; D018080:Receptors, GABA-B; D011978:Receptors, Nicotinic; C510079:conotoxin alpha-RgIA, Conus regius; C085075:CGP 55845A; C507383:alpha-conotoxin Vc1.1