Na(V)1.8 channels are expressed in large, as well as small, diameter sensory afferent neurons

Sensory neurons in the dorsal root ganglia (DRG) express a subset of voltage dependent sodium channels (Na(V)) including Na(V)1.1, 1.6, 1.7, 1.8 and 1.9. Previous work supported preferential localization of Na(V)1.8 channels to small-medium diameter, nociceptive afferent neurons. However, we recently published evidence that Na(V)1.8 was the dominant Na(V) channel expressed in the somas of small, medium and large diameter muscle afferent neurons, which is consistent with other reports. Here, we extend those results to show that Na(V)1.8 expression is not correlated with afferent neuron diameter. Using immunocytochemistry, we found Na(V)1.8 expression in ~50% of sensory afferent neurons with diameters ranging from 20 to 70 µm. In addition, electrophysiological analysis shows that the kinetic and inactivation properties of Na(V)1.8 current are invariant with neuron size. These data add further support to the idea that Na(V)1.8 contributes to the electrical excitability of both nociceptive and non-nociceptive sensory neurons.