Abstract
The TRPV4 Ca(2+)-permeable channel is sensitive to mechanical stimuli. In the current study we have employed immunocytochemical staining in kidney slices and functional assessments (Ca(2+) imaging) in isolated, split-opened, tubule segments to define TRPV4 sites of expression and flow-dependent function in the collecting duct system. Staining patterns revealed strong expression of TRPV4 along the entire collecting duct system with highest levels at the apical (luminal)/subapical region of the principal cells (PCs), the dominant cell type, with more diffuse staining in intercalated cells (ICs). Using fluorescence Ca(2+) imaging and the selective TRPV4 agonist, GSK1016790A, we demonstrated functional TRPV4 channels in PCs and ICs of split-opened cortical collecting ducts and connecting tubules. The agonist was ineffective in inducing a rise in [Ca(2+)](i) in the absence of extracellular Ca(2+) or in tubules from TRPV4-deficient animals. Most importantly, a 10-fold elevation in luminal (apical) fluid flow induced a rapid and sustained influx of Ca(2+) that was abolished by the TRPV channel inhibitor, ruthenium red, or in tubules isolated from TRPV4 deficient animals. We concluded that TRPV4 is highly expressed along the entire collecting duct system where it appears to function as a sensor/transducer of flow-induce mechanical stresses.