The α 2δ auxiliary subunit reduces affinity of ω-conotoxins for recombinant N-type (Ca v2.2) calcium channels

Abstract

The ω-conotoxins from fish-hunting cone snails are potent inhibitors of voltage-gated calcium channels. The ω-conotoxins MVIIA and CVID are selective N-type calcium channel inhibitors with potential in the treatment of chronic pain. The β and α 2δ-1 auxiliary subunits influence the expression and characteristics of the α 1B subunit of N-type channels and are differentially regulated in disease states, including pain. In this study, we examined the influence of these auxiliary subunits on the ability of the ω-conotoxins GVIA, MVIIA, CVID and analogues to inhibit peripheral and central forms of the rat N-type channels. Although the β3 subunit had little influence on the on- and off-rates of ω-conotoxins, co-expression of α 2δ with α 1B significantly reduced on-rates and equilibrium inhibition at both the central and peripheral isoforms of the N-type channels. The α 2δ also enhanced the selectivity of MVIIA, but not CVID, for the central isoform. Similar but less pronounced trends were also observed for N-type channels expressed in human embryonic kidney cells. The influence of α 2δ was not affected by oocyte deglycosylation. The extent of recovery from the ω-conotoxin block was least for GVIA, intermediate for MVIIA, and almost complete for CVID. Application of a hyperpolarizing holding potential (-120 mV) did not significantly enhance the extent of CVID recovery. Interestingly, [R10K]MVIIA and [O10K]GVIA had greater recovery from the block, whereas [K10R]CVID had reduced recovery from the block, indicating that position 10 had an important influence on the extent of ω-conotoxin reversibility. Recovery from CVID block was reduced in the presence of α 2δ in human embryonic kidney cells and in oocytes expressing α 1B-b These results may have implications for the antinociceptive properties of ω-conotosins, given that the α 2δ subunit is up-regulated in certain pain states.