Abstract
We studied the localization and physiological functions of the transient receptor potential (TRP) channels TRPV1 (TRP vanilloid 1) and TRPV4 (TRP vanilloid 4) in the mouse bladder, because both channels are thought to be mechanosensors for bladder distention. RT-PCR specifically amplified TRPV4 transcripts from the urothelial cells, whereas TRPV1 transcripts were barely detectable. ISH experiments showed that TRPV4 transcripts were abundantly expressed in the urothelium, whereas TRPV1 transcripts were not detectable in the urothelial cells. Immunoblotting and IHC studies showed that TRPV4 proteins were mainly localized at the basal plasma membrane domains of the basal urothelial cells. In contrast, TRPV1-immunoreactivities were found not in the urothelial cells but in the nerve fibers that innervate the urinary bladder. In Ca(2+)-imaging experiments, 4alpha-phorbol 12,13-didecanoate, a TRPV4 agonist, and hypotonic stimuli induced significant increases in intracellular calcium ion concentration ([Ca(2+)](i)) in isolated urothelial cells, whereas capsaicin, a TRPV1 agonist, showed no marked effect on the cells. These findings raise the possibility that, in mouse urothelial cells, TRPV4 may contribute to the detection of increases in intravesical pressure related to the micturition reflex.