Kubota S, Kani K, Kitasato H
Department of Ophthalmology, Shiga University of Medical Science, Ohtsu, Japan.
Jpn J Ophthalmol. 1998 Jan-Feb;42(1):12-21. doi: 10.1016/s0021-5155(97)00111-1.
Regulation of fluid flow through corneal stroma was investigated in the bullfrog. Corneal specimens were mounted by clamping their limbal sclera between the two chambers of a Ussing-type chamber. The epithelial surface was covered with Ringer's solution, while the endothelial surface was superfused with Ringer's solution at various pressures ranging from 0-60 mm Hg. At 0 mm Hg, the cornea swelled, while at 10 mm Hg the corneal thickness remained unchanged. Further elevation of the hydrostatic pressure of the endothelial superfusion solution caused a decrease in corneal thickness, suggesting that the hydrostatic pressure in the in vivo frog corneal stroma is about 10 mm Hg. At 10 mm Hg of endothelial superfusion pressure, piercing the epithelial cell layer with a 30-gauge needle caused only slight corneal swelling. Removing glucose from the epithelial perfusion solution induced a slowly progressing increase in corneal thickness. Iodoacetate did not interfere with the swelling of the pierced cornea after the removal of glucose from the epithelial perfusion solution. To examine the possibility that the interstitial fluid flows across the stroma-scleral boundary, corneal specimens having unclamped sclera were incubated in Ringer's solution containing 3 mmol/L dextran of various molecular weights ranging from 8800-162,000, and the volume of the preparation was monitored by sequential measurement of the weight. In the presence of dextran with a molecular weight higher than 70,000, the corneal volume decreased at the beginning of incubation, and after reaching the minimal volume it slowly increased, indicating that the stroma-scleral boundary is permeable to dextran of even a molecular weight of 162,000, although dextran molecules diffuse much more slowly than water, and the concentration of unfilterable solutes in the stroma is lower than 3 mmol/L. In experiments using the Ussing-type chamber at 10 mm Hg of endothelial superfusion pressure, a decrease of NaCl in the superfusing solution to 1/2 caused rapid corneal swelling followed by slow recovery. Adding NaCl to the 1/2 NaCl Ringer's solution caused a further corneal thinning in a concentration-dependent manner. The same extent of decrease in corneal thickness as induced by adding NaCl was achieved by the same concentration of glucose as of NaCl, implying that the value of the reflection coefficient of the endothelial cell layer to either Na+ or Cl- is about half that of glucose. Our results show that even a small difference in the concentration of low molecular weight solutes (e.g., Na+ and Cl-) exerts a force that draws water from the cornea.
对牛蛙角膜基质中液体流动的调节进行了研究。通过将角膜标本的角膜缘巩膜夹在Ussing型小室的两个腔室之间来进行固定。上皮表面覆盖林格氏液，而内皮表面则在0 - 60 mmHg的不同压力下用林格氏液进行灌流。在0 mmHg时，角膜肿胀，而在10 mmHg时角膜厚度保持不变。进一步提高内皮灌流液的静水压力会导致角膜厚度减小，这表明蛙体内角膜基质中的静水压力约为10 mmHg。在内皮灌流压力为10 mmHg时，用30号针头刺穿上皮细胞层仅引起轻微的角膜肿胀。从上皮灌流液中去除葡萄糖会导致角膜厚度缓慢增加。在上皮灌流液中去除葡萄糖后，碘乙酸并不影响被刺穿角膜的肿胀。为了研究间质液是否会穿过基质 - 巩膜边界，将巩膜未夹紧的角膜标本置于含有分子量从8800 - 162,000不等的3 mmol/L右旋糖酐的林格氏液中孵育，并通过连续测量重量来监测标本的体积。在存在分子量高于70,000的右旋糖酐的情况下，孵育开始时角膜体积减小，达到最小体积后又缓慢增加，这表明即使是分子量为162,000的右旋糖酐也能透过基质 - 巩膜边界，尽管右旋糖酐分子的扩散速度比水慢得多，且基质中不可滤过溶质的浓度低于3 mmol/L。在内皮灌流压力为10 mmHg的Ussing型小室实验中，将灌流液中的NaCl浓度降至1/2会导致角膜迅速肿胀，随后缓慢恢复。向1/2 NaCl林格氏液中添加NaCl会以浓度依赖的方式导致角膜进一步变薄。与添加NaCl引起的角膜厚度减小程度相同的情况，由与NaCl浓度相同的葡萄糖实现，这意味着内皮细胞层对Na⁺或Cl⁻的反射系数值约为葡萄糖的一半。我们的结果表明，即使低分子量溶质（如Na⁺和Cl⁻）浓度的微小差异也会产生从角膜吸水的力。
