Figure 1.

Schematic of a Na⁺ channel and drug-binding sites. The four domains of the pore-forming α subunit are shown together with two β sheets (β1 and β2). Each domain is composed of six segments (S1–S6). The pore-lining segments are shown in green (S5–S6), while the voltage-sensitive (S4) segments are shown in yellow. A part of the amino acid sequence in the S4 segments of the fourth domain is shown enlarged in the lower panel. The particular amino acids in positions 1764 and 1771 are shown in blue as they are believed to be involved in the binding of anti-arrhythmic drugs such as lidocaine and flecainide. Adapted from fig. 2 of Schauer & Catterall (2006).