Chou C L, Ma T, Yang B, Knepper M A, Verkman A S
Laboratory of Kidney and Electrolyte Metabolism, National Institutes of Health, Bethesda, Maryland 20892-1603, USA.
Am J Physiol. 1998 Feb;274(2):C549-54. doi: 10.1152/ajpcell.1998.274.2.C549.
Aquaporin (AQP)-3 and AQP4 water channels are expressed at the basolateral membrane of mammalian collecting duct epithelium. To determine the contribution of AQP4 to water permeability in the initial inner medullary collecting duct (IMCD), osmotic water permeability (Pf) was compared in isolated perfused IMCD segments from wild-type and AQP4 knockout mice. The AQP4 knockout mice were previously found to have normal gross appearance, survival, growth, and kidney morphology and a mild urinary concentrating defect (T. Ma, B. Yang, A. Gillespie, E. J. Carlson, C. J. Epstein, and A. S. Verkman, J. Clin. Invest. 100: 957-962, 1997). Transepithelial Pf was measured in microdissected IMCDs after 18-48 h of water deprivation and in the presence of 0.1 nM arginine vasopressin (to make basolateral Pf rate limiting). Pf values (37 degrees C; means +/- SE in cm/s x 10(-3)) were 56.0 +/- 8.5 for wild-type mice (n = 5) and 13.1 +/- 3.7 for knockout mice (n = 6) (P < 0.001). Northern blot analysis of kidney showed that transcript expression of AQP1, AQP2, AQP3, and AQP6 were not affected by AQP4 deletion. Immunoblot analysis indicated no differences in protein expression of AQP1, AQP2, or AQP3, and immunoperoxidase showed no differences in staining patterns. Coexpression of AQP3 and AQP4 in Xenopus laevis oocytes showed additive water permeabilities, suggesting that AQP4 deletion does not affect AQP3 function. These results indicate that AQP4 is responsible for the majority of basolateral membrane water movement in IMCD but that its deletion is associated with a very mild defect in urinary concentrating ability.
水通道蛋白（AQP）-3和AQP4水通道表达于哺乳动物集合管上皮细胞的基底外侧膜。为了确定AQP4对初始髓质内层集合管（IMCD）水通透性的作用，比较了野生型和AQP4基因敲除小鼠分离灌注的IMCD节段的渗透水通透性（Pf）。先前发现AQP4基因敲除小鼠外观、存活、生长及肾脏形态正常，但有轻度尿浓缩缺陷（T.马、B.杨、A.吉莱斯皮、E.J.卡尔森、C.J.爱泼斯坦和A.S.韦克曼，《临床研究杂志》100:957 - 962，1997）。在禁水18 - 48小时后且存在0.1 nM精氨酸加压素（使基底外侧Pf成为限速因素）的情况下，对显微解剖的IMCD测量跨上皮Pf。Pf值（37℃；单位为cm/s×10⁻³，均值±标准误）野生型小鼠（n = 5）为56.0±8.5，基因敲除小鼠（n = 6）为13.1±3.7（P < 0.001）。肾脏的Northern印迹分析表明，AQP1、AQP2、AQP3和AQP6的转录本表达不受AQP4缺失的影响。免疫印迹分析表明AQP1、AQP2或AQP3的蛋白表达无差异，免疫过氧化物酶染色显示染色模式无差异。AQP3和AQP4在非洲爪蟾卵母细胞中的共表达显示水通透性具有加和性，提示AQP4缺失不影响AQP3功能。这些结果表明，AQP4是IMCD基底外侧膜大部分水转运的原因，但其缺失与尿浓缩能力的非常轻微缺陷有关。
