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This article is part of the supplement: 18th Scientific Symposium of the Austrian Pharmacological Society (APHAR)

Open Access Meeting abstract

A conformational change of the domain IV S6 segment of the voltage-gated sodium channel during inactivation

Vaibhavkumar S Gawali, René Cervenka, Péter Lukács, Xaver Koenig, Lena Rubi, Ágnes K Mike, Karlheinz Hiber and Hannes Todt*

Author Affiliations

Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria

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BMC Pharmacology and Toxicology 2012, 13(Suppl 1):A60  doi:10.1186/2050-6511-13-S1-A60

The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/2050-6511/13/S1/A60


Published:17 September 2012

© 2012 Gawali et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background

In voltage-gated Na+ channels the S6 transmembrane segment of domain IV (DIV-S6) is part of the lining of the inner part of the pore. It is of pivotal importance for inactivation gating. We recently showed that amino acid I1581 of DIV-S6 (rNaV1.4 amino acid numbering) is extraordinarily sensitive to both local and distal mutations suggesting a unique role in coupling of voltage-sensor movements to conformational changes in the pore. To date the only structural information relevant to voltage-gated Na+ channels can be derived from the recently crystallized bacterial channel NaVAb. In this structure the amino acid homologous to I1581 faces the lipid phase and is in close spacial relationship to the voltage-sensing apparatus. If this arrangement holds true for the eukaryotic Na+ channel then site 1581 should not be exposed to bulk solution.

Methods

The following methods were used: site-directed mutagenesis of amino acids in the S6 segment of domain IV of the rNaV1.4 channel; heterologous expression of the constructs in tsA 201 cells and Xenopus laevis oocytes; exploration of the kinetic effects of the mutations and gating sensitivity of the amino acid residue in the S6 segment of domain IV of the rNaV1.4 channel by whole-cell patch clamp and two-electrode voltage clamp technique.

Results

We tested the hypothesis by replacing I1581 by a titrable histidine. In wild-type channels changing the pH of the bulk solution from 7.4 to 8.2 had no effect on the voltage-dependence of fast inactivation. However, in I1581H the same change in pH resulted in a 9.51 ± 1.98 mV hyperpolarizing shift (p < 0.05) of the voltage-dependence of fast inactivation.

Conclusions

The data suggest that during inactivation site 1581 is at least partially exposed to the bulk solution and not completely embedded in the lipid phase. The DIV-S6 segment may undergo a conformational change during inactivation, most likely a rotational movement, which allows access of external protons to site 1581.

Acknowledgements

This study was funded by the Austrian Science Fund FWF (grants P210006-B11 and W1232-B11).