TRPV4 in Porcine Lens Epithelium Regulates Hyposmotic Stress‐Induced ATP Release and Na, K‐ATPase Activity

Abstract

In several tissues TRPV4 channels are involved in the response to hyposmotic challenge. Our objective was to detect TRPV4 protein in porcine lens epithelium and its role in hyposmotic stress‐induced ATP release.The Western blot analysis showed presence of TRPV4 in the lens epithelial homogenate. The TRPV4 antagonist RN 1734 (10μM) completely prevented ATP release by lenses exposed to hyposmotic (200 mOsm) solution. Lenses exposed to a TRPV4 agonist, GSK1016790A (GSK), or to hyposmotic solution displayed ATP release and an increased ability of propidium iodide (PI) (MW 668) to enter the epithelium. The increases in PI uptake and ATP release both were abolished by a mixture of agents that block connexin and pannexin hemichannels, 18á‐glycyrrhetinic acid (AGA, 100μM) and probenecid (1mM). An increase in Na, K‐ATPase activity was detected in the epithelium of lenses exposed to GSK in isosmotic solution and the response was prevented by AGA + probenecid. TRPV4 antagonists prevented the activation of Src family kinase and increase of Na, K‐ATPase activity that occurred in the epithelium of lenses exposed to hyposmotic solution.The findings are consistent with hyposmotic shock‐induced TRPV4 channel activation which triggers hemichannel‐mediated ATP release. The results point to a pivotal role for TRPV4 activation as an initial event in a multi‐step response of the lens to hyposmotic stress.