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Nicholas A Delamere, Amritlal Mandal, Mohammad Shahidullah; The influence of TRPV4 ion channel blockade on lens water content.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6403. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In previous studies we reported detection of TRPV4 ion channels in porcine lens epithelium but not fibers. Activation of TRPV4 has been implicated in a mechanism that activates Na,K-ATPase activity in the epithelium in response to swelling of the lens fiber mass. Active transport by the epithelium plays a critical role in ion homeostasis for the entire lens cell mass. Because water homeostasis and ion homeostasis are linked, we tested the possible impact of TRPV4 channel blockade on lens water content.
Na,K-ATPase activity was measured by quantifying ouabain-sensitive ATP hydrolysis. Water content was measured by drying the lens for 40h to completely remove water, then determining the difference between wet and dry weight. Dried lenses were digested in 30% nitric acid and sodium content was measured by atomic absorption spectrophotometry.
After 5 min, Na,K-ATPase activity was increased by 64.1±3.7% (n=6) in the epithelium removed from intact porcine lenses subjected to a swelling challenge by deposit of 5 μl hyperosmotic mannitol solution into the posterior fiber mass. Na,K-ATPase activity in the epithelium also was increased (93.0±5.0%; n=6) in lenses exposed to a TRPV4 agonist GSK1016790A (10nM). The TRPV4 antagonist HC067047 (10 μM) prevented the Na,K-ATPase responses. Porcine as well as rat lenses exposed to 10 μM HC067047 in isosmotic Krebs solution for 90 min displayed a significant net weight gain. HC-treated rat lenses showed an average weight gain of 2.2±0.2 mg (n=4) compared to 0.2±.01 mg (n=11) in control lenses. The sodium content of HC067047-treated rat lenses was 72.2±10.4 (n=3) compared to 42.4±2.8 (n=9) μmoles/gm dry weight in control lenses.
The findings are consistent with a role for TRPV4 in the mechanism that regulates Na,K-ATPase activity in the lens epithelium. At steady state, intermittent TRPV4 activation may contribute to fine tuning of Na,K-ATPase activity. On the basis of these studies we suggest that Na,K-ATPase regulation, in turn, influences lens water homeostasis.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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