Selective silencing of Na V 1.7 decreases excitability and conduction in vagal sensory neurons

• Published in: The Journal of physiology Vol. 589; no. 23; pp. 5663 - 5676
• Main Authors: Muroi, Yukiko, Ru, Fei, Kollarik, Marian, Canning, Brendan J., Hughes, Stephen A., Walsh, Stacey, Sigg, Martin, Carr, Michael J., Undem, Bradley J.
• Format: Journal Article
• Language: English
• Published: 01-12-2011
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2011.215384

Non‐technical summary 
Sodium channels are obligatory for the conduction of action potentials along axons. There are several different sodium channel subtypes expressed in vagal sensory neurons, and it is difficult to pharmacologically block these subtypes selectively. We used virally delivered shRNA to selectively block the production of one of the sodium channel subtypes expressed in vagal sensory neurons, namely Na
V
1.7, and found that by selectively inhibiting the expression of this channel the conduction of action potentials was blocked in the majority of vagal sensory neurons. This study also shows that Na
V
1.7 is required for the elicitation of classical vagal reflexes such as cough.
Abstract 
There has been much information learned in recent years about voltage gated sodium channel (Na
V
) subtypes in somatosensory pain signalling, but much less is known about the role of specific sodium channel subtypes in the vagal sensory system. In this study, we developed a technique using adeno‐associated viruses (AAVs) to directly introduce shRNA against Na
V
1.7 subtype gene into the vagal sensory ganglia of guinea pigs 
in vivo
. Na
V
1.7 gene expression in nodose ganglia was effectively and selectively reduced without influencing the expression of other sodium channel subtype genes including Na
V
1.1, 1.2, 1.3 1.6, 1.8, or 1.9. Using a whole cell patch‐clamp technique, this effect on Na
V
1.7 gene expression coincided with a reduction in tetrodotoxin‐sensitive sodium current, a requirement for much larger depolarizing stimulus to initiate action potentials, and reduction in repetitive action potential discharge. Extracellular recordings in the isolated vagus nerve revealed that the conduction of action potentials in sensory A‐ and C‐fibres in many neurons was effectively abolished after Na
V
1.7 shRNA introduction. Moreover, bilateral Na
V
1.7 shRNA injected animals survived for several months and the vagal reflex behaviour, exemplified by citric acid‐induced coughing, was significantly suppressed. These data indicate that selectively silencing Na
V
1.7 ion channel expression leads to a substantial decrease in neural excitability and conduction block in vagal afferent nerves.