Biophysical and Pharmacological Characterisation of Native Human NaV1.8 Channels from Isolated Dorsal Root Ganglia (DRG)

Abstract

NaV1.8 is a tetrodotoxin resistant (TTX-r) sodium channel expressed in sensory neurones that has a depolarised activation threshold, slow inactivation kinetics and a recovers rapidly from inactivation compared to tetrodotoxin sensitive (TTX-s) channels (Cummins & Waxman 1997; Akopian et al., 1996). These biophysical properties mean that NaV1.8 contributes to both electrogenesis and the maintenance of repetitive firing of action potentials (Blair & Bean 2002; Renganathan et al., 2001; Waxman et al., 2001). The expression and biophysical properties of NaV1.8 can be modulated by ongoing nociceptive input and findings in the literature strongly support a key role for NaV1.8 in pain signalling (England et al., 1996; Roza et al., 2003; Kerr et al., 2001; Coward et al., 2000; Akopian et al., 1999). The selective NaV1.8 antagonist A803467 has provided further evidence for a role of NaV1.8 in nociceptive sensory input (Jarvis et al., 2007) however characterisation and pharmacology of native NaV1.8 currents has been shown using cells isolated from non human species. We have characterised NaV1.8 currents recorded from TTX-r channels in human DRG and shown that they can be inhibited by a selective modulator of TTX-r current, A803467. Isolated currents had a V1/2 inactivation of −35 mV and a V1/2 of activation of −10 mV. Action potentials evoked by increasing current injections were inhibited by TTX and by the selective NaV1.8 modulator A803467 which abolished repetitive firing. Furthermore, we have compared the biophysical properties of the native channel with those of recombinantly expressed human NaV1.8 channel. This work not only provides a means by which we can assess the biophysics and pharmacological modulation of native human NaV1.8 currents, but will also help us to understand the role of the channel in human pain signalling.