The formation of disulfide bridges is a classical approach used to study 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, Cu²⁺(1,10-phenanthroline)₃ (CuPhen). 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. 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 Cu²⁺ ions. Our results indicate an use- and voltage-dependent binding and unbinding of CuPhen, reminiscent of the lidocaine quaternary derivative QX-314 and the neurotoxin batrachotoxin. 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.