Aims: 

Voltage gated ion channels consist of an ion conducting central pore, several gates and voltage sensors. In the voltage-gated Na channel the central pore is believed to be lined by the S6 segments of all four domains, which may contain the activation and inactivation gates. The voltage sensors extend radially from the central pore axis. We sought to investigate a possible electrostatic coupling of the permeation pathway to the voltage sensors.

Methods: 

A critical residue within the putative selectivity filter of the rNav1.4 channel, K1237 was replaced by the negatively charged glutamate (K1237E). The constructs were expressed in Xenopus laevis oocytes and studied by means of the two electrode voltage clamp technique. Results:

In K1237E the midpoint of fast inactivation (V05) was shifted to the hyperpolarized direction relative to wild-type (-60 ± 13 vs. -47 ± 11 mV, n = 6, P < 0.01). Such shift is consistent with an electrostatic bias on the voltage-sensors by the introduced negative charge in the outer vestibule. Furthermore, we generated serial replacements by cysteines of 16 residues in the domain IV-S6 segment. These mutations generated inconsistent changes of V05. However, when these mutations were combined with the K1237E mutation, V05 was shifted to more negative values in all but one double mutants, irrespective of the direction and the amount of shift produced by the single S6 mutation (mean shift = -13 ± 5 mV).

Conclusion: 

The pore of the voltage-gated Na channel is electrostatically coupled to the voltage sensor for fast inactivation.

Support: Austrian Science Fund P17509-B11.