Selective Interaction of Local Anesthetics with a Peptide Derived from the Voltage-Gated Na + Channel

Sodium channels are concentrated in axons and muscle and have an overall architecture similar to those of K + and Ca 2+ channels consisting of α and β subunits. The α-subunit (260 kDa) is composed of four homologous domains (I-IV), each containing six transmembrane segments (S1-S6). Recently, many authors, using site-directed mutagenesis, have shown that IV/S4-S5 loop is a good candidate for being involved in Na + channel inactivation process, and, therefore, a possible site of local anesthetics (LA) interaction. In this work, we used NMR to study the interaction of two Las , namely, benzocaine (BZC) and lidocaine (LDC), with a fragment of IV/S4-S5 loop, comprising residues 1466-1486, KGIRTLLFALMMSLPALFNIG-NH 2 (Chan1). DOSY experiments provide evidence for a possible formation of a complex between LAs and Chan1. TOCSY and 15 N-HSQC experiments have been used to monitor the change of the chemical shift of αCH, NH and 15 N of Chan1 upon increasing addition of LAs up to 2 mM. For LDC, no significant changes were observed. By contrast, in the case of BZC, changes of αCH and 15 N chemical shift for the residues in the region L 10 -S 13 were detected. Overall, our data show that the interaction of the local anesthetics with Na + channel seems to be specific for BZC, which is able to perturb some structural features of Chan1 and is non-specific for LDC. This distinct behavior is most likely associated with the physico-chemical properties of BZC, which is neutral and more hydrophobic than LDC .