Nejsum L N, Kwon T H, Marples D, Flyvbjerg A, Knepper M A, Frøkiaer J, Nielsen S
Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000 Aarhus C., Denmark.
Am J Physiol Renal Physiol. 2001 Apr;280(4):F715-26. doi: 10.1152/ajprenal.2001.280.4.F715.
Diabetes mellitus (DM) is associated with osmotic diuresis and natriuresis. At day 15, rats with DM induced by streptozotocin (n = 13) had severe hyperglycemia (27.1 +/- 0.4 vs. 4.7 +/- 0.1 mM in controls) and had a fivefold increase in water intake (123 +/- 5 vs. 25 +/- 2 ml/day) and urine output. Semiquantitative immunoblotting revealed a significant increase in inner medullary AQP2 (201 +/- 12% of control rats, P < 0.05) and phosphorylated (Ser(256)) AQP2 (p-AQP2) abundance (299 +/- 32%) in DM rats. Also, the abundance of inner medullary AQP3 was markedly increased to 171 +/- 19% of control levels (100 +/- 4%, n = 7, P < 0.05). In contrast, the abundance of whole kidney AQP1 (90 +/- 3%) and inner medullary AQP4 (121 +/- 16%) was unchanged in rats with DM. Immunoelectron microscopy further revealed an increased labeling of AQP2 in the apical plasma membrane of collecting duct principal cells (with less labeling in the intracellular vesicles) of DM rats, indicating enhanced trafficking of AQP2 to the apical plasma membrane. There was a marked increase in urinary sodium excretion in DM. Only Na(+)/H(+) exchanger NHE3 was downregulated (67 +/- 10 vs. 100 +/- 11%) whereas there were no significant changes in abundance of type 2 Na-phosphate cotransporter (128 +/- 6 vs. 100 +/- 10%); the Na-K-2Cl cotransporter (125 +/- 19 vs. 100 +/- 10%); the thiazide-sensitive Na-Cl cotransporter (121 +/- 9 vs. 100 +/- 10%); the alpha(1)-subunit of the Na-K-ATPase (106 +/- 7 vs. 100 +/- 5%); and the proximal tubule Na-HCO(3) cotransporter (98 +/- 16 vs. 100 +/- 7%). In conclusion, DM rats had an increased AQP2, p-AQP2, and AQP3 abundance as well as high AQP2 labeling of the apical plasma membrane, which is likely to represent a vasopressin-mediated compensatory increase in response to the severe polyuria. In contrast, there were no major changes in the abundance of AQP1, AQP4, and several major proximal and distal tubule Na(+) transporters except NHE3 downregulation, which may participate in the increased sodium excretion.
糖尿病（DM）与渗透性利尿和利钠作用相关。在第15天，用链脲佐菌素诱导糖尿病的大鼠（n = 13）出现严重高血糖（27.1±0.4 vs. 对照组4.7±0.1 mM），水摄入量（123±5 vs. 25±2 ml/天）和尿量增加了五倍。半定量免疫印迹显示糖尿病大鼠髓质内AQP2显著增加（为对照大鼠的201±12%，P < 0.05）以及磷酸化（Ser(256)）AQP2（p-AQP2）丰度显著增加（为299±32%）。此外，髓质内AQP3的丰度显著增加至对照水平的171±19%（100±4%，n = 7，P < 0.05）。相比之下，糖尿病大鼠全肾AQP1（90±3%）和髓质内AQP4（121±16%）的丰度未发生变化。免疫电子显微镜进一步显示糖尿病大鼠集合管主细胞顶端质膜上AQP2的标记增加（细胞内囊泡中的标记减少），表明AQP2向顶端质膜的转运增强。糖尿病大鼠尿钠排泄显著增加。仅Na(+)/H(+)交换体NHE3下调（67±10 vs. 100±11%），而2型钠-磷酸盐共转运体（128±6 vs. 100±10%）；Na-K-2Cl共转运体（125±19 vs. 100±10%）；噻嗪类敏感的Na-Cl共转运体（121±9 vs. 100±10%）；Na-K-ATP酶的α(1)亚基（106±7 vs. 100±5%）；以及近端小管Na-HCO(3)共转运体（98±16 vs. 100±7%）的丰度无显著变化。总之，糖尿病大鼠的AQP2、p-AQP2和AQP3丰度增加，以及顶端质膜上AQP2标记较高，这可能代表了抗利尿激素介导的对严重多尿的代偿性增加。相比之下，除NHE3下调外，AQP1、AQP4以及近端和远端小管几种主要的Na(+)转运体的丰度无重大变化，NHE3下调可能参与了钠排泄增加。
