The effect of zinc on the stiffness of chicken lenses

Abstract

Aims/Purpose: Aquaporins are specialized water channels. A volume change through permeable aquaporins may be necessary for the lens' ability to change shape during accommodation1. This study aimed to determine the effects of zinc2, an agonist that increases aquaporin 0 (AQP0) permeability in oocytes, on the biomechanics of chicken lenses.Methods: White Leghorn chickens (Gallus gallus domesticus, N = 6) were sacrificed at 14 days of age. Both eyes were enucleated and lenses were dissected in Tyrode's solution (TS). One lens from each bird was treated with zinc chloride (80 μg/mL in TS for 15 min, at room temperature; RT), while the other lens (control lens) was incubated in TS (15 min, RT). Lenses were compressed (CellScale Micro Tester G2) to test their biomechanical integrity. For each lens, force‐compression data were generated by the MicroTester G2 software (ver. 1.0.0.1) and fit to a three‐parameter exponential curve with the equation y = y0 + aebx; the unitless b‐coefficient of the exponential equation was used to assess stiffness as it describes how rapidly the force increases as the compression distance increases. B‐coefficients from each curve were extracted and the effects of zinc treated versus control lenses were analysed using a paired t‐test.Results: The b‐coefficient value for zinc‐treated lenses averaged to 4.2 ± 0.8 while the mean value for control lenses was significantly (p = 0.01) lower at 3.2 ± 0.5, indicating that zinc‐treated lenses were stiffer.Conclusions: The compression data show a zinc‐associated increase in lens stiffness. AQP0 typically plays a role in allowing water to enter, but not exit, the lens, therefore zinc may have led to an increase in water content, resulting in stiffer lenses. However, water permeability was not measured in this study, therefore the AQP0‐associated mechanism of lens stiffening cannot be confirmed. Further study is needed to determine zinc's action on the biomechanics of the lens.References1. Gerometta R, Candia OA. A decrease in the permeability of aquaporin zero as a possible cause for presbyopia. Medical Hypotheses. 2016 Jan 1;86:132–4.2. Németh‐Cahalan KL, Kalman K, Froger A, Hall JE. Zinc modulation of water permeability reveals that aquaporin 0 functions as a cooperative tetramer. The Journal of general physiology. 2007 Nov;130(5):457–64.