IP sub(3) sensitizes TRPV4 channel to the mechano- and osmotransducing messenger 5'-6'-epoxyeicosatrienoic acid

Mechanical and osmotic sensitivity of the transient receptor potential vanilloid 4 (TRPV4) channel depends on phospholipase A sub(2) (PLA sub(2)) activation and the subsequent production of the arachidonic acid metabolites, epoxyeicosatrienoic acid (EET). We show that both high viscous loading and hypotonicity stimuli in native ciliated epithelial cells use PLA sub(2)-EET as the primary pathway to activate TRPV4. Under conditions of low PLA sub(2) activation, both also use extracellular ATP-mediated activation of phospholipase C (PLC)-inositol trisphosphate (IP sub(3)) signaling to support TRPV4 gating. IP sub(3), without being an agonist itself, sensitizes TRPV4 to EET in epithelial ciliated cells and cells heterologously expressing TRPV4, an effect inhibited by the IP sub(3) receptor antagonist xestospongin C. Coimmunoprecipitation assays indicated a physical interaction between TRPV4 and IP sub(3) receptor 3. Collectively, our study suggests a functional coupling between plasma membrane TRPV4 channels and intracellular store Ca super(2+) channels required to initiate and maintain the oscillatory Ca super(2+) signal triggered by high viscosity and hypotonic stimuli that do not reach a threshold level of PLA sub(2) activation.