Correlation of the electrophysiological profiles and sodium channel transcripts of individual rat dorsal root ganglia neurons.

Olivier Thériault ,Mohamed Chahine

doi:10.3389/fncel.2014.00285

Abstract

Voltage gated sodium channels (Nav channels) play an important role in nociceptive transmission. They are intimately tied to the genesis and transmission of neuronal firing. Five different isoforms (Nav1.3, Nav1.6, Nav1.7, Nav1.8, and Nav1.9) have been linked to nociceptive responses. A change in the biophysical properties of these channels or in their expression levels occurs in different pathological pain states. However, the precise involvement of the isoforms in the genesis and transmission of nociceptive responses is unknown. The aim of the present study was to investigate the synergy between the different populations of Nav channels that give individual neurons a unique electrophysical profile. We used the patch-clamp technique in the whole-cell configuration to record Nav currents and action potentials from acutely dissociated small diameter DRG neurons (<30 μm) from adult rats. We also performed single cell qPCR on the same neurons. Our results revealed that there is a strong correlation between Nav currents and mRNA transcripts in individual neurons. A cluster analysis showed that subgroups formed by Nav channel transcripts by mRNA quantification have different biophysical properties. In addition, the firing frequency of the neurons was not affected by the relative populations of Nav channel. The synergy between populations of Nav channel in individual small diameter DRG neurons gives each neuron a unique electrophysiological profile. The Nav channel remodeling that occurs in different pathological pain states may be responsible for the sensitization of the neurons.

Highlights

Voltage gated sodium channels (Nav channels) play an important role in nociceptive transmission and are intimately tied to the genesis and transmission of neuronal action potentials
We evaluated the efficiency of the qPCR by generating standard curves over a wide range of mRNA copies using serial dilutions of known concentrations of cDNA (Supplement Figure 2A)
One concern with qPCR is that the amount of amplified mRNA is not proportional to the amount of functional protein (Greenbaum et al, 2003; Maier et al, 2009)

Summary

Introduction

Voltage gated sodium channels (Nav channels) play an important role in nociceptive transmission and are intimately tied to the genesis and transmission of neuronal action potentials. The slow closed-state inactivation of Nav1.7 is thought to play an important role in the amplification of subthreshold depolarization and initiate AP firing in neurons (Blair and Bean, 2002; Cummins et al, 2007). The fast recuperation from the inactivated state of Nav1.8 is thought to sustain the relatively high frequency firing of small DRG neurons (Cummins and Waxman, 1997; Renganathan et al, 2001) while the current induced by the hyperpolarized activation of Nav1.9 could modulate the membrane voltage and alter the neuronal excitability (Herzog et al, 2001)

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