Bladder afferent sensitivity in wild-type and TRPV1 knockout mice.

Rodolfo Testa

Rodolfo Testa

Rodolfo Testa

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In knockout mice lacking the transient receptor potential vanilloid 1 (TRPV1) ion channel, in vitro low-threshold bladder afferents were shown to be attenuated during distension of the bladder with no changes in the pressure/volume relationship, while high threshold afferent sensitivity was unchanged, suggesting that these channels are involved in normal bladder function.

The ‘‘vanilloid’’ receptor TRPV1 is a non-specific ion channel activated by capsaicin, heat, protons, and endogenous ligands.

In the lower urinary tract (LUT), it is expressed in various structures, including the mucosa and the muscular layer, in non-neuronal structures, such as the urothelium and interstitial cells, as well as on detrusor myocytes. Despite increasing knowledge about the structure, properties, and distribution of the TRPV1 receptor, its functional role in the normal LUT has not been yet established. TRPV1 receptor may have a defined role in pain perception, control of bladder reflex activity in pathological states, and in cellular differentiation. TRPV1 has been involved in the regulation of the frequency of bladder reflex contractions, either through direct excitation of sensory fibers or through the urothelial cells' or interstitial cells' afferent fiber signaling pathway, including release of mediators from the urothelium {1}. A previously published paper {2} demonstrated that inhibition of TRPV1 in isolated rat bladder significantly reduced the volume-evoked rise in contractile amplitude, suggesting an involvement of TRPV1 in the activity induced by stretch. Liu et al. {3} reported that the symptoms of sensory urgency were associated with the increased expression of TRPV1 mRNA in the trigonal mucosa, and that TRPV1 may play a role in sensory urgency and premature first bladder sensation on filling. Our knowledge about the functional role of TRPV1 receptors in the LUT, and on endogenous activators of these receptors is incomplete and further research is needed; nevertheless, the present paper may represent a leap in our understanding of their importance.