Regional resistivity variations in lens homogenates

Abstract

The response of the lens to changes in the distribution and concentration of electrolytes can be measured by characterizing the changes in resistivity that occur secondary to variations in intracellular composition. Regional intracellular cytoplasmic resistivities of lens fiber cells can be approximated by homogenates isolated from the cortex and nucleus of the lens. The cortical, transitional, and nuclear calf lens homogenate resistivities at physiologic water concentrations were established to be 186.04 +/- 12.79, 297.69 +/- 18.95, and 421.74 +/- 69.64 omega cm respectively. The physiologic water content of the calf lens is 70.25 +/- 0.94% in the cortex and 54.33 +/- 1.28% in the nucleus. These data suggest that the increasing cortico-nuclear resistivity gradient is accompanied by a decreasing electrolyte concentration and a progressive cortico-nuclear dehydration. The corresponding mature bovine cortical and nuclear homogenate resistivities are 204.82 +/- 13.92 and 628.30 +/- 111.81 omega cm. When compared with calf homogenates the mature bovine cortical resistivity is nearly identical; while the elevated nuclear resistivity is attributable to a continual nuclear dehydration that occurs secondary to aging. Resistivity measurements performed on decapsulated lens homogenates reveal a close correspondence between calf and human lenses. Whereas, the elevated resistivity of the mature bovine decapsulated lens homogenate is attributable to a progressively dehydrated nucleus that increases in size with age. Supplementary data gathered from hydration and dehydration experiments performed on cortical and nuclear homogenates were used to characterize anatomical variations in resistivity as a function of total water content. These data indicate that the resistivity of the cortical homogenate is inversely proportional to the electrolyte concentration, whereas the resistivity of the nuclear homogenate is primarily dependent upon the mobilities of the electrolyte species with the highest concentrations. As the water concentration of the nuclear homogenate is increased to non-physiologic levels the resistivity becomes concentration-dependent, and is no longer is no longer dominated by the mobility.