Multiple gating processes associated with the distal end of the S6 segment of domain II in the Nav channels

Voltage-gated sodium (Nav) channels are transmembrane proteins that play crucial roles in the initiation and propagation of action potentials (APs) in excitable tissues such as the heart, muscles, and nerves. The distal ends of the four domain S6 segments of Nav channels contain hydrophobic residues, which form an intracellular gate. This gate allows Nav channels to control ion flux in excitable cells by opening and closing. However, the mechanism of the distal end of Domain II (DII) S6 segment in channel gating remains unclear. In this study, using whole-cell patch clamp recording, we systematically investigated the biophysical characteristics of various mutants L811 site (located at the distal end of the DII S6 segment) of Nav1.9 and the corresponding L796P mutant of Nav1.4. We found that the mutations significantly shifted the activation and inactivation curves, slowed the fast inactivation, accelerated the slow inactivation and use-dependent slow inactivation, and L811P altered the ion selectivity of the channel. Therefore, our findings suggest that the distal end of the DII S6 segment in Nav channels plays a pivotal role in regulating multiple gating processes.