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Nicholas A Delamere, Mohammad Shahidullah; TRPV4 channels enable the lens epithelium to respond to remote damage in the fiber mass.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3561. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Na,K-ATPase activity is low or absent in lens fiber cells and Na,K-ATPase activity in the epithelium plays a critical role in ion and water homeostasis of the entire lens structure. We know from previous studies that Na,K-ATPase activity in the epithelium is subject to regulation by a TRPV4- and Src family tyrosine kinase-dependent mechanism. Here we tested whether the epithelium is able to increase Na,K-ATPase activity in response to a remote stimulus in the fiber mass.
The posterior pole of the intact pig lens was subjected to localized damage by a 2.5 mm diameter freeze-thaw wound (FT) then the lens was incubated for 2-30 min at 37 oC. At the end of the incubation period the lens epithelium was removed, homogenized and the rate of ouabain-sensitive ATP hydrolysis (Na,K-ATPase activity) measured or TRPV4 protein expression and Src family tyrosine kinase (SFK) activation in the epithelium were examined by a western blot approach. Data were analyzed by a t-test.<br />
Localized freeze-thaw (FT) damage to lens fibers at posterior pole was found to cause SFK activation in the epithelium judged by an increase of pY416 SFK band intensity (treated:control = 4.3±0.8, p=0.001, n=3). The FT maneuver caused Na,K-ATPase activity to almost double (60.0±5.6 vs 33.1±6.3 nmoles ATP hydrolyzed/mg protein/30 min, p=0.001, n=5). The changes occurred within minutes. The lens expresses a mechanosensitive ion channel, TRPV4, and here we examined its distribution. TRPV4 protein was detected in the lens epithelium but not in the fiber cells. A TRPV4 channel antagonist, HC067947 (10 µM) suppressed the SFK phosphorylation response in lenses subjected to the FT maneuver (treated:control = 1.4±0.8, n=3). The FT-induced increase of Na,K-ATPase activity in the epithelium was suppressed in lenses exposed to either HC067947 or the SFK inhibitor PP2 (10 µM).
The findings point to a TRPV4-dependent mechanism that impacts Na,K-ATPase activity in the lens epithelium. The mechanism enables lens epithelial cells to sense remote damage in the fiber mass and respond by activating SFK and increasing Na,K-ATPase activity.
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