Inactivation properties of sodium channel Nav1.8 maintain action potential amplitude in small DRG neurons in the context of depolarizationReportar como inadecuado

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Molecular Pain

, 3:12

First Online: 31 May 2007Received: 17 May 2007Accepted: 31 May 2007


BackgroundSmall neurons of the dorsal root ganglion DRG express five of the nine known voltage-gated sodium channels. Each channel has unique biophysical characteristics which determine how it contributes to the generation of action potentials AP. To better understand how AP amplitude is maintained in nociceptive DRG neurons and their centrally projecting axons, which are subjected to depolarization within the dorsal horn, we investigated the dependence of AP amplitude on membrane potential, and how that dependence is altered by the presence or absence of sodium channel Nav1.8.

ResultsIn small neurons cultured from wild type WT adult mouse DRG, AP amplitude decreases as the membrane potential is depolarized from -90 mV to -30 mV. The decrease in amplitude is best fit by two Boltzmann equations, having V1-2 values of -73 and -37 mV. These values are similar to the V1-2 values for steady-state fast inactivation of tetrodotoxin-sensitive TTX-s sodium channels, and the tetrodotoxin-resistant TTX-r Nav1.8 sodium channel, respectively. Addition of TTX eliminates the more hyperpolarized V1-2 component and leads to increasing AP amplitude for holding potentials of -90 to -60 mV. This increase is substantially reduced by the addition of potassium channel blockers. In neurons from Nav1.8- mice, the voltage-dependent decrease in AP amplitude is characterized by a single Boltzmann equation with a V1-2 value of -55 mV, suggesting a shift in the steady-state fast inactivation properties of TTX-s sodium channels. Transfection of Nav1.8- DRG neurons with DNA encoding Nav1.8 results in a membrane potential-dependent decrease in AP amplitude that recapitulates WT properties.

ConclusionWe conclude that the presence of Nav1.8 allows AP amplitude to be maintained in DRG neurons and their centrally projecting axons even when depolarized within the dorsal horn.

Electronic supplementary materialThe online version of this article doi:10.1186-1744-8069-3-12 contains supplementary material, which is available to authorized users.

T Patrick Harty and Stephen G Waxman contributed equally to this work.

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Autor: T Patrick Harty - Stephen G Waxman


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