Analgesic α-conotoxins Vc1.1 and Rg1A inhibit N-type calcium channels in sensory neurons of α9 nicotinic receptor knockout mice

Abstract

α-Conotoxins Vc1.1 and Rg1A 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 α9α10 nicotinic acetylcholine receptor (nAChR) selective-conotoxins Vc1.1 and Rg1A 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 Ca2+ channels but inhibits them via GABAB receptor activation. The present study investigated Vc1.1 and Rg1A inhibition of N-type Ca2+ channels currents in DRG neurons of wild-type and α9 knockout (KO) mice to determine if the α9 nAChR was necessary for inhibition of the Ca2+ channel current. Application of Vc1.1 (100 nM) inhibited N-type Ca2+ channel currents to 69.2 ± 3.5% of control in DRG neurons isolated from wild-type mice. In {greater than or equal to >70% of DRG neurons isolated from the α9 KO mice, both Vc1.1 and Rg1A selectively inhibited N-type Ca2+ channel currents with an IC50 of 24.6 nM and 22.4 nM, respectively. The GABAB receptor antagonist CGP55845 (1 μM) antagonized the effect of Vc1.1 and Rg1A on the N-type Ca2+ channels in α9 KO mice. RT-PCR and western blot analysis confirmed the absence of the α9 nAChR in mice carrying a null mutation for the nAChR α9 gene. These results demonstrate that the inhibition of N-type Ca2+ channel channels by Vc1.1 and Rg1A is not mediated by the expression of α9α10 nAChRs in DRG neurons.