Differential Localizations of the Transient Receptor Potential Channels TRPV4 and TRPV1 in the Mouse Urinary Bladder

Takahiro Yamada ¹, Shinya Ugawa ¹, Takashi Ueda ¹, Yusuke Ishida ¹, Kenji Kajita ¹ and Shoichi Shimada ^1*

¹ Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya, Japan

^* To whom correspondence should be addressed. E-mail: sshimada{at}med.nagoya-cu.ac.jp.

Submitted on May 25, 2008
Accepted on 4 November 2008

	Abstract

We investigated 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 (reverse transcription-polymerase chain reaction) specifically amplified TRPV4 transcripts from the urothelial cells, while TRPV1 transcripts were barely detectable. In situ hybridization experiments revealed that TRPV4 transcripts were abundantly expressed in the urothelia, whereas TRPV1 transcripts were not detectable in the urothelial cells. Immunoblotting and immunohistochemical 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 Ca²⁺-imaging experiments, 4-phorbol 12,13-didecanoate (4-PDD), a TRPV4 agonist, and hypotonic stimuli induced significant increases in the intracellular calcium ion concentration ([Ca²⁺]_i) in isolated urothelial cells, whereas capsaicin, a TRPV1 agonist, displayed 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.

Key Words: urinary bladder, transient receptor potential vanilloid 1, transient receptor potential vanilloid 4, RT–PCR, in situ hybridization, immunohistochemistry, immunoelectron microscopy, calcium imaging, mouse

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