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, 4␣-phorbol 12,13-didecanoate (4␣-PDD) evoked Ca 2؉ influx in wild-type (WT) urothelial cells, but not in TRPV4-deficient (TRPV4KO) cells. We established a cellstretch system to investigate stretch-evoked changes in intracellular Ca 2؉ concentration and ATP release. Stretch stimulation evoked intracellular Ca 2؉ increases in a stretch speed-and distance-dependent manner in WT and TRPV4KO cells. In TRPV4KO urothelial cells, however, the intracellular Ca 2؉ increase in response to stretch stimulation was significantly attenuated compared with that in WT cells. Stretch-evoked Ca 2؉ 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 4␣-PDD 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 Ca 2؉ . 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. Transient receptor potential vanilloid 4 (TRPV4),3 a member of the TRP superfamily of cation channels, is a Ca 2ϩ -permeable channel activated by a wide variety of physical and chemical stimuli (1, 2). TRPV4 was originally viewed as an osmo-or mechano-sensor, because the channel opens in response to hypotonicity-induced cell swelling (3-5) and shear stress (6). Alternatively, TRPV4 can be activated by diverse chemical stimuli such as synthetic phorbol ester 4␣-phorbol 12,13-didecanoate (4␣-PDD) (7), a botanical agent (bisandrographolide A), anandamide metabolites such as arachidonic acid and epoxyeicosatrienoic acids, as well as moderate warmth (Ͼ27°C) (8 -10). TRPV4 is widely expressed throughout the body, including renal epithelium, auditory hair cells, skin keratinocytes, hippocampus neurons, endothelial cells, and urinary bladder epithelium, thereby contributing to numerous physiological processes such as osmoregulation (11, 12), hearing (13), thermal and mechanical hyperalgesia (14, 15), neural activity in the brain (16), skin barrier recovery (17), and cell volume regulation (18). Therefore, the TRPV4 channel is now considered a multimodal transducer in various tissues and cells.Non-neuronal cells within the urinary bladder wall (notably the transitional epithelial cells (urothelial cells)) function as a barrier against ions, solutes, and infection and also participate in the detection of physical and chemical stimuli (19 -21). The urothelium expresses various sensory receptors and channe...

To understand the mechanistic basis of cold temperature stress and the role of the auxin response, we characterized root growth and gravity response of Arabidopsis thaliana after cold stress, finding that 8 to 12 h at 48C inhibited root growth and gravity response by ;50%. The auxin-signaling mutants axr1 and tir1, which show a reduced gravity response, responded to cold treatment like the wild type, suggesting that cold stress affects auxin transport rather than auxin signaling. Consistently, expression analyses of an auxin-responsive marker, IAA2-GUS, and a direct transport assay confirmed that cold inhibits root basipetal (shootward) auxin transport. Microscopy of living cells revealed that trafficking of the auxin efflux carrier PIN2, which acts in basipetal auxin transport, was dramatically reduced by cold. The lateral relocalization of PIN3, which has been suggested to mediate the early phase of root gravity response, was also inhibited by cold stress. Additionally, cold differentially affected various protein trafficking pathways. Furthermore, the inhibition of protein trafficking by cold is independent of cellular actin organization and membrane fluidity. Taken together, these results suggest that the effect of cold stress on auxin is linked to the inhibition of intracellular trafficking of auxin efflux carriers.