Tetrodotoxin-sensitive voltage-gated sodium channels regulate bladder afferent responses to distension

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a prevalent, chronic bladder disorder that negatively impacts the quality of life for; 5% of the western population. Hypersensitivity of mechanosensory afferents embedded within the bladder wall is considered a key component in mediating IC/BPS symptoms. Bladder infusion of voltage-gated sodium (Na-v) channel blockers show clinical efficacy in treating IC/BPS symptoms; however, the current repertoire of Na-v channels expressed by and contributing to bladder afferent function is unknown. We used single-cell reverse-transcription polymerase chain reaction of retrogradely traced bladder-innervating dorsal root ganglia (DRG) neurons to determine the expression profile of Na-v channels, and patch-clamp recordings to characterise the contribution of tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na-v channels to total sodium current and neuronal excitability. Wedetermined the TTX-S and TTX-R contribution to mechanosensitive bladder afferent responses ex vivo and spinal dorsal horn activation in vivo. Single-cell reverse-transcription polymerase chain reaction of bladder-innervating DRG neurons revealed significant heterogeneity in Na-v channel coexpression patterns. However, TTX-S Na-v channels contribute the vast majority of the total sodium current density and regulate the neuronal excitability of bladder DRG neurons. Furthermore, TTX-S Na-v channels mediate almost all bladder afferent responses to distension. In vivo intrabladder infusion of TTX significantly reduces activation of dorsal horn neurons within the spinal cord to bladder distension. These data provide the first comprehensive analysis of Na-v channel expression within sensory afferents innervating the bladder. They also demonstrate an essential role for TTX-S Na-v channel regulation of bladder-innervating DRG neuroexcitability, bladder afferent responses to distension, and nociceptive signalling to the spinal cord.