Emory Univ. Renal Division, Atlanta, GA 30322, USA.
Am J Physiol Renal Physiol. 2013 Jan 1;304(1):F103-11. doi: 10.1152/ajprenal.00385.2012. Epub 2012 Nov 7.
The regulation of the inner medullary collecting duct (IMCD) urea transporters (UT-A1, UT-A3) and aquaporin-2 (AQP2) and their interactions in diabetic animals is unknown. We investigated whether the urine concentrating defect in diabetic animals was a function of AQP2, the UT-As, or both transporters. UT-A1/UT-A3 knockout (UT-A1/A3 KO) mice produce dilute urine. We gave wild-type (WT) and UT-A1/A3 KO mice vasopressin via minipump for 7 days. In WT mice, vasopressin increased urine osmolality from 3,000 to 4,550 mosmol/kgH(2)O. In contrast, urine osmolality was low (800 mosmol/kgH(2)O) in the UT-A1/A3 KOs and remained low following vasopressin. Surprisingly, AQP2 protein abundance increased in UT-A1/A3 KO (114%) and WT (92%) mice. To define the role of UT-A1 and UT-A3 in the diabetic responses, WT and UT-A1/A3 KO mice were injected with streptozotocin (STZ). UT-A1/A3 KO mice showed only 40% survival at 7 days post-STZ injection compared with 70% in WT. AQP2 did not increase in the diabetic UT-A1/A3 KO mice compared with a 133% increase in WT diabetic mice. Biotinylation studies in rat IMCDs showed that membrane accumulation of UT-A1 increased by 68% in response to vasopressin in control rats but was unchanged by vasopressin in diabetic rat IMCDs. We conclude that, even with increased AQP2, UT-A1/UT-A3 is essential to optimal urine concentration. Furthermore, UT-A1 may be maximally membrane associated in diabetic rat inner medulla, making additional stimulation by vasopressin ineffective.
内髓集合管 (IMCD) 尿素转运体 (UT-A1、UT-A3) 和水通道蛋白-2 (AQP2) 的调节及其在糖尿病动物中的相互作用尚不清楚。我们研究了糖尿病动物的尿浓缩缺陷是否是 AQP2、UT-As 或这两种转运体的功能。UT-A1/UT-A3 敲除 (UT-A1/A3 KO) 小鼠产生稀释的尿液。我们通过微泵给野生型 (WT) 和 UT-A1/A3 KO 小鼠给予加压素 7 天。在 WT 小鼠中，加压素使尿液渗透压从 3000 增加到 4550 mosmol/kgH(2)O。相比之下，UT-A1/A3 KO 中的尿液渗透压较低 (800 mosmol/kgH(2)O)，并且在加压素后仍保持较低水平。令人惊讶的是，AQP2 蛋白丰度在 UT-A1/A3 KO (114%) 和 WT (92%) 小鼠中增加。为了确定 UT-A1 和 UT-A3 在糖尿病反应中的作用，我们给 WT 和 UT-A1/A3 KO 小鼠注射链脲佐菌素 (STZ)。与 WT 相比，UT-A1/A3 KO 小鼠在 STZ 注射后 7 天仅存活 40%。与 WT 糖尿病小鼠的 133%增加相比，糖尿病 UT-A1/A3 KO 小鼠中的 AQP2 没有增加。在大鼠 IMCD 中的生物素标记研究表明，在对照大鼠中，加压素使 UT-A1 的膜积累增加了 68%，但在糖尿病大鼠 IMCD 中加压素没有改变。我们的结论是，即使 AQP2 增加，UT-A1/UT-A3 对于最佳尿浓缩也是必不可少的。此外，UT-A1 在内髓质中可能与膜最大程度相关联，使得加压素的额外刺激无效。
