Volume sensing in the transient receptor potential vanilloid 4 ion channel is cell type–specific and mediated by an N-terminal volume-sensing domain

Abstract

Many retinal diseases are associated with pathological cell swelling, but the underlying etiology remains to be established. A key component of the volume-sensitive machinery, the transient receptor potential vanilloid 4 (TRPV4) ion channel, may represent a sensor and transducer of cell swelling, but the molecular link between the swelling and TRPV4 activation is unresolved. Here, our results from experiments using electrophysiology, cell volumetric measurements, and fluorescence imaging conducted in murine retinal cells and <i>Xenopus</i> oocytes indicated that cell swelling in the physiological range activated TRPV4 in Müller glia and <i>Xenopus</i> oocytes, but required phospholipase A₂ (PLA₂) activity exclusively in Müller cells. Volume-dependent TRPV4 gating was independent of cytoskeletal rearrangements and phosphorylation. Our findings also revealed that TRPV4-mediated transduction of volume changes is dependent by its N terminus, more specifically by its distal-most part. We conclude that the volume sensitivity and function of TRPV4 <i>in situ</i> depend critically on its functional and cell type-specific interactions.