Interaction of SNX482 with Domains III and IV Inhibits Activation Gating of α1E (CaV2.3) Calcium Channels

Abstract

We have investigated the action of SNX482, a toxin isolated from the venom of the tarantula Hysterocrates gigas, on voltage-dependent calcium channels expressed in tsa-201 cells. Upon application of 200 nM SNX482, R-type alpha(1E) calcium channels underwent rapid and complete inhibition, which was only poorly reversible upon washout. However, upon application of strong membrane depolarizations, rapid and complete recovery from inhibition was obtained. Tail current analysis revealed that SNX482 mediated an approximately 70 mV depolarizing shift in half-activation potential, suggesting that the toxin inhibits alpha(1E) calcium channels by preventing their activation. Experiments involving chimeric channels combining structural features of alpha(1E) and alpha(1C) subunits indicated that the presence of the domain III and IV of alpha(1E) is a prerequisite for a strong gating inhibition. In contrast, L-type alpha(1C) channels underwent incomplete inhibition at saturating concentrations of SNX482 that was paralleled by a small shift in half-activation potential and which could be rapidly reversed, suggesting a less pronounced effect of the toxin on L-type calcium channel gating. We conclude that SNX482 does not exhibit unequivocal specificity for R-type channels, but highly effectively antagonizes their activation.

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

“…Ca V 2.3 channel inhibitors could potentially have a beneficial effect in seizure disorders and as pain therapeutics ; however, these channels do not have a particularly rich pharmacology and selective small organic inhibitors of Ca V 2.3 channels are lacking . They are inhibited by the spider toxin SNX-482 (Newcomb et al, 1998); however, this toxin also targets Ca V 1.2 LTCCs (Bourinet et al, 2001) and A-type K + currents (Kimm and Bean, 2014) and is thus not selective.…”

“…It too produces poorly reversible inhibition, unless the membrane is repetitively depolarized-an action that allows the voltage sensors of the channel to dislodge the bound toxin . Several other spider toxins fall into the category of gating inhibitors, including a-grammotoxin SIA, a peptide that is isolated from the venom of the tarantula Grammostola spatulata and inhibits both Ca V 2.2 and Ca V 2.1 channels (Lampe et al, 1993;McDonough et al, 1997), and the Ca V 2.3 channel blocker SNX-482 from the tarantula Hysterocrates gigas (Bourinet et al, 2001).…”

Four Novel Tarantula Toxins as Selective Modulators of Voltage-Gated Sodium Channel Subtypes

“…One of the characteristics of gating modifier toxins is that whereas they mediate complete inhibition of all inward currents, outward currents can still be observed despite the presence of the toxin (McDonough et al, 1997;Bourinet et al, 2001). CcoTx2 (50 nM) apparently changes the voltage dependence of gating of Na v 1.2/␤ 1 , so channels do not open in response to the moderate depolarizations that evoke inward current through unblocked channels (Fig.…”

Developmental Biology of Neoplastic Growth

“…These residues are part of the voltage sensor of the channel, a crucial region that is also the target for spider gating modifier toxins interacting with the S3C helix of Kv2 and Kv4 channels (Diochot et al 1999;Swartz and MacKinnon 1997;Wang et al 2004). Studies performed on mutated K + , Na + , and Ca 2+ channels with spider toxins suggest a conserved binding motif for gating modifier toxins within the S3C region of the voltage-sensing domain of these channels (Bourinet et al 2001;Li-Smerin and Swartz 1998;Ruta and MacKinnon 2004;Winterfield and Swartz 2000). This could also be the case for sea anemone gating modifier toxins.…”