TRPV1 enhances the afferent response to P2X receptor activation in the mouse urinary bladder

Both TRPV1 and P2X receptors present on bladder sensory nerve fibres have been implicated in mechanosensation during bladder filling. The aim of this study was to determine possible interactions between these receptors in modulating afferent nerve activity. In wildtype (TRPV1(+/+)) and TRPV1 knockout (TRPV1(-/-)) mice, bladder afferent nerve activity, intravesical pressure, and luminal ATP and acetylcholine levels were determined and also intracellular calcium responses of dissociated pelvic DRG neurones and primary mouse urothelial cells (PMUCs). Bladder afferent nerve responses to the purinergic agonist alpha beta Methylene-ATP were depressed in TRPV1(-/-) mice (p <= 0.001) and also in TRPV1(+/+) mice treated with the TRPV1-antagonist capsazepine (10 mu M; p <= 0.001). These effects were independent of changes in bladder compliance or contractility. Responses of DRG neuron to alpha beta Methylene-ATP (30 mu M) were unchanged in the TRPV1(-/-) mice, but the proportion of responsive neurones was reduced (p <= 0.01). Although the TRPV1 agonist capsaicin (1 mu M) did not evoke intracellular responses in PMUCs from TRPV1(+/+) mice, luminal ATP levels were reduced in the TRPV1(-/-) mice (p <= 0.001) compared to wildtype. TRPV1 modulates P2X mediated afferent responses and provides a mechanistic basis for the decrease in sensory symptoms observed following resiniferatoxin and capsaicin treatment for lower urinary tract symptoms.