The T type calcium channel CaV3.2 regulates bladder afferent responses to mechanical stimuli.

The bladder wall is innervated by a complex network of afferent nerves that detect bladder stretch during filling. Sensory signals, generated in response to distension, are relayed to the spinal cord and brain to evoke physiological and painful sensations and regulate urine storage and voiding. Hyperexcitability of these sensory pathways is a key component in the development of chronic bladder hypersensitivity disorders including interstitial cystitis/bladder pain syndrome and overactive bladder syndrome. Despite this, the full array of ion channels that regulate bladder afferent responses to mechanical stimuli have yet to be determined. Here we investigated the role of low-voltage activated T-type calcium (CaV3) channels in regulating bladder afferent responses to distension. Using single-cell reverse-transcription polymerase chain reaction and immunofluorescence we revealed ubiquitous expression of CaV3.2, but not CaV3.1 or CaV3.3 in individual bladder-innervating dorsal root ganglia (DRG) neurons. In an ex vivo bladder-nerve recording preparation pharmacological inhibition of CaV3.2 with TTA-A2 and ABT-639, selective blockers of T-type calcium channels, dose-dependently attenuated bladder afferent responses to distension in the absence of changes to muscle compliance. Further evaluation revealed CaV3.2 blockers significantly inhibited both low- and high-threshold afferents, decreasing peak responses to distension, and delaying activation thresholds, thereby attenuating bladder afferent responses to both physiological and noxious distension. Nocifensive visceromotor responses to noxious bladder distension in-vivo were also significantly reduced by inhibition of CaV3 with TTA-A2. Together these data provide evidence of a major role for CaV3.2 in regulating bladder afferent responses to bladder distension and nociceptive signalling to the spinal cord.