Age-dependent changes in resistivity and electrolytes related to lens development and growth in the rat.

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.