Mitton K P, Hess J L, Bunce G E
Department of Biochemistry and Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg 24061-0308, USA.
Invest Ophthalmol Vis Sci. 1995 Apr;36(5):914-24.
Lenses from selenite-treated animals develop reversible "cold cataract" at a lower temperature than is required for lenses from age-matched control animals. This unexplained, stabilized phase transition is readily observed in intact lenses 36 to 48 hours after treatment and occurs in lenses before the appearance of the irreversible nuclear opacity observed 72 to 96 hours after treatment. The objective of this study was to investigate factors that may be responsible for this difference.
Preweanling rats were injected with sodium selenite. Lens extracellular water volume was measured using 14C-inulin. Free amino acids were analyzed using precolumn derivatization and high performance liquid chromatography. Soluble protein was isolated from lenses of control, and treated animals and temperature-dependent changes in light scattering were measured at 490 nm.
Lens extracellular water was increased by the selenite treatment, with a concurrent 10% decrease in intracellular volume. Solutions of soluble protein from lenses of selenite-treated animals after postinjection hours 24 and 48 had higher critical phase transition temperatures (Tc) compared to similar proteins from control lenses. From 24 to 72 hours after injection, the free amino acid content of the lens increased 42%. Taurine levels were unchanged over the same period. The addition of 7 mM glycine and 7 mM proline to solutions of soluble protein (96 mg ml-1) decreased the phase transition temperature. Taurine (14 mM) had a similar effect. Combining taurine and the glycine plus proline solutions had an additive effect in lowering the Tc.
Increases in free amino acid concentration occur in lenses in response to the stress imposed by a systemic dose of selenite. The altered polyion content in lenses from selenite-treated animals, before nuclear cataract formation, contributes to the greater thermal stability of transparency in these lenses, thus lowering the temperature at which "cold cataract" forms.
经亚硒酸盐处理的动物晶状体在比年龄匹配的对照动物晶状体形成可逆性“冷性白内障”所需温度更低的情况下就会出现这种情况。这种无法解释的、稳定的相变在处理后36至48小时的完整晶状体中很容易观察到，并且发生在处理后72至96小时观察到的不可逆核混浊出现之前的晶状体中。本研究的目的是调查可能导致这种差异的因素。
对断奶前大鼠注射亚硒酸钠。使用14C-菊粉测量晶状体细胞外水体积。使用柱前衍生化和高效液相色谱分析游离氨基酸。从对照动物和处理动物的晶状体中分离可溶性蛋白质，并在490nm处测量光散射的温度依赖性变化。
亚硒酸盐处理使晶状体细胞外水增加，同时细胞内体积减少10%。与对照晶状体的类似蛋白质相比，注射后24小时和48小时经亚硒酸盐处理的动物晶状体的可溶性蛋白质溶液具有更高的临界相变温度（Tc）。注射后24至72小时，晶状体的游离氨基酸含量增加了42%。在此期间牛磺酸水平未发生变化。向可溶性蛋白质溶液（96mg/ml）中添加7mM甘氨酸和7mM脯氨酸可降低相变温度。牛磺酸（14mM）有类似作用。将牛磺酸与甘氨酸加脯氨酸溶液组合在降低Tc方面具有相加作用。
晶状体中游离氨基酸浓度的增加是对全身剂量亚硒酸盐施加的应激的反应。在核性白内障形成之前，经亚硒酸盐处理的动物晶状体中改变的聚离子含量有助于这些晶状体中透明度更高的热稳定性，从而降低“冷性白内障”形成的温度。
