Asgeirsson Daniel, Venturoli Daniele, Rippe Bengt, Rippe Catarina
Dept. of Nephrology, Univ. Hospital of Lund, S-211 85 Lund, Sweden.
Am J Physiol Renal Physiol. 2006 Nov;291(5):F1083-9. doi: 10.1152/ajprenal.00488.2005. Epub 2006 May 30.
It is established that the glomerular filter sieves macromolecules based on their size, shape, and charge. Anionic proteins are thus retarded compared with their neutral or cationic counterparts. However, recent studies have indicated that charge effects are small, or even "anomalous," for polysaccharides. We therefore investigated the impact of charge on the glomerular permeability to polysaccharides by comparing sieving coefficients (theta; primary urine-to-plasma concentration ratio) for negatively charged, carboxymethylated (CM) FITC-Ficoll and FITC-dextran with their neutral counterparts. For these probes, theta were determined in anesthetized Wistar rats [269 +/- 2.7 g (+/-SE; n = 36)], whose ureters were cannulated for urine sampling. The glomerular filtration rate was assessed using FITC-inulin. Polysaccharides were constantly infused, and after equilibration, urine was collected and a midpoint plasma sample was taken. Size and concentration determinations of the FITC-labeled polysaccharides were achieved by size-exclusion HPLC (HPSEC). For CM-Ficoll, theta was significantly increased (32 times at 55 A) compared with that of uncharged Ficoll. A small increase in theta for CM-dextran compared with neutral dextran was also observed (1.8 times at 55 A). In conclusion, negatively charged Ficoll relative to neutral Ficoll was found to be markedly hyperpermeable across the glomerular filter. Furthermore, negatively charged Ficoll was observed to be larger on HPSEC compared with its neutral counterpart of the same molecular weight. It is proposed that the introduction of negative charges in the "dendrimeric," cross-linked Ficoll molecule may alter its configuration, so as to make it more extended, and conceivably, more flexible, thereby increasing its glomerular permeability.
已确定肾小球滤过器根据大分子的大小、形状和电荷对其进行筛分。因此，与中性或阳离子蛋白质相比，阴离子蛋白质的通过受到阻碍。然而，最近的研究表明，电荷对多糖的影响很小，甚至是“反常的”。因此，我们通过比较带负电荷的羧甲基化（CM）异硫氰酸荧光素 - 菲可（FITC - Ficoll）和异硫氰酸荧光素 - 葡聚糖与其中性对应物的筛分系数（θ；原尿与血浆浓度比），研究了电荷对肾小球对多糖通透性的影响。对于这些探针，在麻醉的Wistar大鼠（体重269±2.7 g（±标准误；n = 36））中测定θ，其输尿管插管用于尿液采样。使用异硫氰酸荧光素 - 菊粉评估肾小球滤过率。持续输注多糖，平衡后收集尿液并采集血浆中点样本。通过尺寸排阻高效液相色谱（HPSEC）对异硫氰酸荧光素标记的多糖进行大小和浓度测定。对于CM - 菲可，与不带电荷的菲可相比，θ显著增加（在55 Å时增加32倍）。与中性葡聚糖相比，CM - 葡聚糖的θ也有小幅增加（在55 Å时增加1.8倍）。总之，发现带负电荷的菲可比中性菲可在肾小球滤过器中的通透性明显更高。此外，在HPSEC上观察到，带负电荷的菲可比相同分子量的中性对应物更大。有人提出，在“树枝状”交联的菲可分子中引入负电荷可能会改变其构型，使其更伸展，并且可以想象更灵活，从而增加其肾小球通透性。
