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Nicholas A Delamere, Amritlal Mandal, Richard Mathias, Junyuan Gao, Mohammad Shahidullah; Lens osmotic homeostasis involves TRPV1 channels as well as TRPV4.. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2091. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The lens response to a hyposmotic (swelling) stimulus involves TRPV4-dependent activation of Na,K-ATPase, the Na-K pump. By studying activation of ERK1/2 and other signaling pathways we showed recently that the response to a hyperosmotic (shrinkage) stimulus involves a different ion channel TRPV1. Here, we present studies to determine how lens ion transport mechanisms respond to TRPV1 activation.
Rb uptake by intact porcine lenses was measured by atomic absorption spectrometry. NKCC1 phosphorylation in lens epithelium was detected by western blot analysis. Changes in surface hydrostatic pressure (HP) in the mouse lens were measured using a microelectrode/manometer system.
In porcine lens, hyperosmotic solution (350 mOsm) as well as capsaicin (100 nM) caused an increase of potassium (Rb) uptake from a control value of 0.62±0.01 (p>0.01, n=5) to 0.94±0.04 (p>0.01, n=5, hyperosmotic) and 0.85±0.04 (p>0.01, n=5, capsaicin) mmoles/kg lens water/10 min. Both responses were abolished either by bumetanide (10 µM) or by the TRPV1 antagonist A889425 (1 µM). Ouabain-sensitive Rb uptake was not altered by hyposmotic solution (control 0.39±0.05 vs hyperosmotic 0.39±0.03, p< 0.85, n=4) mmoles/kg lens water/10 min), indicating no significant change of Na-K pump activity. On the other hand, phosphorylation (activation) of NKCC1 was detectable in the epithelium of lenses exposed to hyperosmotic solution or capsaicin for a little as 2.5 min. Phosphorylated NKCC1 band density was increased from a normalized value of 1 to a value of 1.9±0.13(p<0.001, n=4) by hyperosmotic solution and 1.8±0.10 (p<0.001, n=4) by capsaicin. In mouse lens, both hyperosmotic solution and capsaicin transiently increased HP and the recovery phase was abolished by bumetanide.
The findings point to TRPV1-dependent NKCC1 activation in response to either a hyperosmotic stimulus or capsaicin. There was no evidence of altered Na,K-ATPase activity. Taken together, these and earlier studies suggest lens osmotic homeostasis involves a TRPV1-NKCC1 shrinkage response and an opposing TRPV4-Na,K-ATPase swelling response.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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