Cu 2+(1,10 phenanthroline) 3 is an open-channel blocker of the human skeletal muscle sodium channel

Abstract

1 The formation of disulfide bridges is a classical approach used to study the mobility, proximity and distances of residues in a variety of proteins, including ligand- and voltage-gated ion channels. We performed patch-clamp studies to investigate the interaction of a pair of cysteines introduced into the human skeletal muscle voltage-gated Na + channel (hNa v1.4) using the oxidation catalyst, Cu 2+(1,10- phenanthroline) 3 (CuPhen). 2 Our experiments resulted in a surprising finding, a reversible current inhibition of the mutant I1160C/L1482C containing two cysteines in the D3/and D4/S4-S5 loops, subjected to oxidative cross-linking in the presence of CuPhen. 3 We report here that CuPhen is an open channel blocker of both mutant and wild-type (WT) hNa v1.4 channels, however, for WT channels a more than 10-fold higher concentration was needed to induce the same effect. Moreover, 1,10-phenanthroline was capable of blocking Na + channels in the absence of Cu 2+ ions. Our results indicate a use- and voltage-dependent binding and unbinding of CuPhen, reminiscent of the lidocaine quaternary derivative QX-314 and the neurotoxin batrachotoxin. 4 Care should be taken when using CuPhen as an oxidizing reagent in cross-linking experiments, since it may directly affect channel activity. Our results identify CuPhen (and phenantroline) as a novel use-dependent inhibitor of Na + channels, a mechanism that is shared by drugs widely used in the treatment of epilepsy, neuropathic pain, cardiac arrhythmia and myotonia. We hypothesize that I1160C in D3/S4-S5 and the corresponding L1482C mutation in D4/S4-S5 could allosterically affect a binding site located in the inner pore region of the channel. © 2006 Nature Publishing Group All rights reserved.