The TRPV4 cation channel mediates stretch-evoked Ca2+ influx and ATP release in primary urothelial cell cultures

Abstract

Transient receptor potential channels have recently been implicated in physiological functions in a urogenital system. In this study, we investigated the role of transient receptor potential vanilloid 4 (TRPV4) channels in a stretch sensing mechanism in mouse primary urothelial cell cultures. The selective TRPV4 agonist, 4phorbol 12,13-didecanoate (4PDD) evoked Ca2+ influx in wild-type (WT) urothelial cells, but not in TRPV4-deficient (TRPV4KO) cells. We established a cell-stretch system to investigate stretch-evoked changes in intracellular Ca2+ concentration and ATP release. Stretch stimulation evoked intracellular Ca2+ increases in a stretch speed- and distance-dependent manner in WT and TRPV4KO cells. In TRPV4KO urothelial cells, however, the intracellular Ca2+ increase in response to stretch stimulation was significantly attenuated compared with that in WT cells. Stretch-evoked Ca2+ increases in WT urothelium were partially reduced in the presence of ruthenium red, a broad TRP channel blocker, whereas that in TRPV4KO cells did not show such reduction. Potent ATP release occurred following stretch stimulation or 4PDD administration in WT urothelial cells, which was dramatically suppressed in TRPV4KO cells. Stretch-dependent ATP release was almost completely eliminated in the presence of ruthenium red or in the absence of extracellular Ca2+. These results suggest that TRPV4 senses distension of the bladder urothelium, which is converted to an ATP signal in the micturition reflex pathway during urine storage. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.