Functional TRPV4 channels and an absence of capsaicin-evoked currents in freshly-isolated, guinea-pig urothelial cells

Abstract

Previously we have shown that the transient receptor potential vanilloid 4 (TRPV4) channel regulates urinary bladder function, and that TRPV4 is expressed in both smooth muscle and urothelial cell types within the bladder wall (Thorneloe et al. 2008). Urothelial cells have also been suggested to express TRPV1 channels (Birder et al., 2001). Therefore, we enzymatically isolated guinea-pig urothelial cells in an attempt to record TRPV4 and TRPV1-mediated currents. The identity of the isolated cells was confirmed by quantitative PCR for the urothelial marker uroplakin 1A. Whole-cell patch-clamp recordings with the TRPV4 agonist, GSK1016790A, activated urothelial currents with an EC50 of 11 nM that were completely inhibited by the TRPV4 inhibitor ruthenium red (5 µM). Urothelial currents were also activated by challenge with hypotonic extracellular solution (220 mOsm) known to activate TRPV4 channels. However, the TRPV1 agonist capsaicin, which activated TRPV1 currents in HEK cells expressing TRPV1, was unable to evoke current in these freshly-isolated guinea-pig urothelial cells. We demonstrate that TRPV4 channels are functionally expressed at the plasma membrane of freshly-isolated, guinea-pig urothelial cells, further supporting the important role of TRPV4 in urinary bladder physiology.