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Age-dependent changes in resistivity and electrolytes related to lens development and growth in the rat
B Groth-Vasselli1, S Von Hagen, P N Farnsworth
1New Jersey School of Medicine UMD-NJ, Department of Ophthalmology, Newark 07103.
Insights
Lens development in rats shows distinct maturation periods affecting water, ion concentrations, and resistivity. These changes are crucial for understanding age-related cataract susceptibility.
Area of Science:
- Ophthalmology
- Developmental Biology
- Biophysics
Background:
- Lens development involves complex changes in composition and biophysical properties.
- Understanding these changes is key to addressing age-related eye conditions like cataracts.
Purpose of the Study:
- To investigate the dynamic changes in lens resistivity, water content, and cation concentrations during rat lens development and maturation.
- To correlate these biophysical and compositional changes with different developmental stages.
Main Methods:
- Resistivity measurements of lens homogenates.
- Determination of lens percent water content.
- Analysis of sodium (Na) and potassium (K) cation concentrations at various developmental time points.
Main Results:
- Three distinct neonatal periods (pre-CMP, CMP, post-CMP) were identified, each with unique changes in ion concentration, water content, and resistivity.
- A significant rise in resistivity occurred during the pre-CMP (days 5-12) due to declining ion concentration.
- Unexpectedly, resistivity remained stable during the CMP (days 12-16) despite further ion and water decrease.
- Adult nuclear maturation period (NMP, days 30-100) showed decreased ion and water content, with a corresponding rise in resistivity.
- The K/Na ratio stabilized around 4 by day 100.
- Ion concentration and mobility were identified as key determinants of lens resistivity.
Conclusions:
- Lens development is characterized by complex, stage-specific alterations in composition and resistivity.
- These age-related changes likely influence lens susceptibility to cataract formation.
- The study challenges the 'free-flowing' syncytium model of lens structure.
Abstract:
Alterations in resistivity measurements of lens homogenates, lens percent water and cation concentrations of sodium and potassium show a complex pattern in the Sprague-Dawley rat during lens development and maturation. During the neonatal period, the data provide evidence for three distinct periods: days 5-12, a pre-critical maturation period (pre-CMP), a steep decline in cation concentration and a minimal change in percent water were accompanied by an expected sharp rise in resistivity; days 12-16, critical maturation period (CMP), a further decrease in ion concentration and water was concomitant with the unexpected observation of no significant change in resistivity; and days 16-30, post-CMP, no significant changes were observed for cation concentrations, percent water, or resistivity. From 30 to 100 days, an adult nuclear maturation period (NMP), a decrease in cation concentration and percent water was reflected in a rise in resistivity. A comparison of 100 and 500 day lenses revealed that the concentrations of Na and K, and percent water are essentially unchanged. The K/Na ratio, which had decreased from an initial value of 5.9 at 5 days, stabilized at approximately 4 by day 100. A comparison of the resistivity measured in both lens homogenates and KCl solutions at identical molar strengths revealed that, for the ages studied, ion concentration and ion mobility play important roles in determining this parameter. The underlying cause for age related variations in lens susceptibility to cataractogenic insult is most likely related to complex changes in composition and resistivity which undoubtedly reflect adjustments in molecular organization. The proposition that the lens is a 'free flowing' syncytium of cells appears unwarranted.