Schematic representation of the BLM setup and the structure of prokaryotic Na<sub>v</sub>.

<p>(A) The BLM sample chamber and the amplifier. The reference electrode is connected to the <i>trans</i> chamber through a salt bridge and the command electrode is connected to the <i>cis</i> chamber. (B) Top-view of the structure of a full-length prokaryotic Na<sub>v</sub>. The four monomers, highlighted in different colors, assemble along each other to form the ionic conducting pore in the center of the tetrameric structure. Picture is generated based on the X-ray crystal structure of Na<sub>v</sub>Rh (PDB ID 4DXW) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188861#pone.0188861.ref007" target="_blank">7</a>]. (C) Side-view of the same structure in (B). (D) Schematic illustration comparing the structure of eukaryotic and prokaryotic Na<sub>v</sub>s. The four arginine residues on S4 that are responsible for the voltage sensing are denoted by “+” signs. N and C denote the N- and C- termini, respectively.</p>