van Hoek A N, de Jong M D, van Os C H
Department of Physiology, University of Nijmegen, The Netherlands.
Biochim Biophys Acta. 1990 Dec 14;1030(2):203-10. doi: 10.1016/0005-2736(90)90296-z.
The effects of dimethylsulfoxide, DMSO, and mercurial sulfhydryl reagents have been studied on water and small solute permeability of rat renal brush border membrane vesicles. Water and solute permeability was measured by mixing membrane vesicles with hypertonic solutions in a stopped-flow apparatus and following osmotically-induced changes in vesicular volume via changes in scattered light intensity. The rate constant of the fast osmotic shrinkage is proportional to the osmotic water permeability, while the rate constant of the slow reswelling phase is proportional to the solute permeability. Using mannitol as the osmotic agent, the osmotic shrinkage of rat renal brush border membrane vesicles followed a biphasic time course. 80% of the vesicles shrunk with a rate constant of approx. 50 s-1 and 20% with a rate constant of approx. 2 s-1. DMSO decreased dose-dependently the amplitude of the fast osmotic shrinkage, without affecting its rate constant. In contrast to DMSO, HgCl2 decreased the rate constant but not the amplitude of the fast osmotic shrinkage of renal brush border vesicles. Between 40-50 microM HgCl2, the inhibition of the fast osmotic shrinkage was completed. DMSO and HgCl2 increase the activation energy of water permeation in renal membranes from 3 to 12-15 kcal/mol. DMSO and HgCl2 did not affect the rate constant of the slow osmotic shrinkage of renal membrane vesicles and were also without effect on osmotic shrinkage of small intestinal brush border and pure phospholipid vesicles. In renal brush border membranes, HgCl2 at low concentrations (less than 10 microM) increased by 15-fold the permeability to NaCl and urea but not to mannitol, an effect which precedes the inhibition of water permeability at higher HgCl2 concentrations. The increase in small solute permeability was irreversible while the inhibition of water permeability could be reversed with cysteine and dithiothreitol. We conclude that water and small solute pathways in rat renal brush border membranes are completely separate entities, which are effected differently by DMSO and HgCl2. These pathways for water and solutes must be membrane proteins since neither DMSO nor HgCl2 affect the permeability properties of pure phospholipid vesicles.
已研究了二甲基亚砜（DMSO）和汞巯基试剂对大鼠肾刷状缘膜囊泡水及小分子溶质通透性的影响。通过在停流装置中将膜囊泡与高渗溶液混合，并根据散射光强度的变化跟踪渗透压诱导的囊泡体积变化，来测量水和溶质的通透性。快速渗透收缩的速率常数与渗透水通透性成正比，而缓慢再膨胀阶段的速率常数与溶质通透性成正比。以甘露醇作为渗透剂，大鼠肾刷状缘膜囊泡的渗透收缩呈现双相时间进程。80%的囊泡以约50 s⁻¹的速率常数收缩，20%的囊泡以约2 s⁻¹的速率常数收缩。DMSO剂量依赖性地降低快速渗透收缩的幅度，但不影响其速率常数。与DMSO相反，HgCl₂降低了速率常数，但不影响肾刷状缘囊泡快速渗透收缩的幅度。在40 - 50 μM HgCl₂之间，快速渗透收缩的抑制作用完成。DMSO和HgCl₂将肾膜中水渗透的活化能从3 kcal/mol提高到12 - 15 kcal/mol。DMSO和HgCl₂不影响肾膜囊泡缓慢渗透收缩的速率常数，对小肠刷状缘和纯磷脂囊泡的渗透收缩也无影响。在肾刷状缘膜中，低浓度（小于10 μM）的HgCl₂使对NaCl和尿素的通透性增加15倍，但对甘露醇的通透性无影响，这种作用在较高HgCl₂浓度抑制水通透性之前出现。小分子溶质通透性的增加是不可逆的，而水通透性的抑制可用半胱氨酸和二硫苏糖醇逆转。我们得出结论，大鼠肾刷状缘膜中的水和小分子溶质途径是完全独立的实体，DMSO和HgCl₂对它们的影响不同。这些水和溶质的途径必定是膜蛋白，因为DMSO和HgCl₂都不影响纯磷脂囊泡的通透性特性。
