Abstract
Purpose :
Aquaporins are specialized water channels. They are thought to act as part of the ionic current radiator model that brings ions and water in the lens at the anterior and posterior poles, before being pumped out at the equator. A volume change resulting from water flow through the aquaporins may be necessary for the lens' ability to change shape during accommodation; Gerometta et al. (2007) showed that radially stretched lenses from which water was allowed to leave but not allowed to re-enter, could not be restored to their previous shapes. The purpose of this study was to determine the effects of zinc, an agonist that increases aquaporin 0 (AQP0) permeability in oocytes, on the biomechanics of chicken lenses.
Methods :
Hatchling white leghorn chickens (Gallus gallus domesticus, N=6) were purchased and reared for 14 days before being sacrificed. Both eyes were enucleated and immersed in oxygenated Tyrode’s solution (TS). Lenses were dissected out and one lens from each bird was treated with zinc chloride (80 μg/ml in TS for 15 min, RT), while the other lens (control lens) was incubated in TS (15 min, RT). Lenses were then rinsed (fresh TS) before being compressed (CellScale Micro Tester G2) to test their biomechanical integrity. For each lens, force-compression data for were generated by the MicroTester G2 software (ver. 1.0.0.1) and fit to a three-parameter exponential curve with the equation equation y=y0 + aebx; the unitless b-coefficient of the exponential equation describes the relationship of how rapidly the force increases as the compression distance increases, with higher numerical values representing steeper curves and therefore stiffer lenses. B-coefficients from each curve were extracted and the effects of zinc-treated vs control lenses were analysed using a paired t-test.
Results :
The b-coefficient value for zinc-treated lenses averaged to 5.9 ± 1.3 (range:1.9 to 8.4) while the mean value for control lenses was significantly (p = 0.0263) higher at 7.5 ± 1.9 (range: 4.8 to 9.7), indicating that in zinc-treated lenses were softer.
Conclusions :
The compression data showing that treatment with zinc led to softer lenses suggests that, as in oocytes, zinc may also be an agonist of AQP0 in the lens, and also act to increase in water permeability. However, as water permeability was not measured, this mechanism of lens softening cannot be confirmed. Further study is needed to determine zinc's action on the biomechanics of the lens.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.