目的:肾脏表达水通道蛋白3(AQP3)在尿浓缩机制中起着极其重要的作用.AQP3缺失小鼠表现为尿浓缩功能严重障碍.为阐明这种基因缺失的生理特性和发生机制,我们利用AQP3基因敲除小鼠和野生型小鼠复制急性尿素负荷动物模型,对其作用机制及影响进行研究.方法:对小鼠实施急性尿素负荷,从实验前2 h到尿素负荷后第8 h,每隔2 h收集1次尿样分别检测尿量、尿渗透压及尿素浓度.分离肾脏组织RNA进行实时荧光定量RT-PCR反应.应用Western blotting分析肾组织中尿素转运蛋白(UTs)的变化.结果:给予尿素后4 h左右,2种不同基因型小鼠均有负荷尿素的排泄.尿素负荷后AQP3缺失小鼠尿的渗透压和尿素含量逐渐增高,第 8 h,几乎与野生型小鼠值相等,但尿中非尿素溶质浓度却没有改变.在最后4 h内尿量下降到基础值的1/4.AQP3基因缺失和野生型小鼠尿素负荷显著地上调了UT-A3的表达.结论:AQP3基因缺失并没有直接干扰肾脏对尿素的浓缩功能,但却减弱了对尿中其它溶质浓缩的能力.这种对溶质选择性的反应是由于AQP3对水和尿素转运能力的不同所致.结果表明AQP3对尿中非尿素溶质的浓缩具有特殊作用.%AIM: Aquaporin 3 ( AQP3 ) water channel expressed in the kidney plays a critical role in the urine concentrating mechanism. Mice with AQP3 deletion show a urinary concentrating defect. To better characterize this defect, we studied the influence and mechanism of an acute urea load in conscious AQP3 - null and wild - type mice. METHODS:Urine was collected and assayed every 2 h, from 2 h before (baseline) to 8 h after the urea load. Urine volume, urine osmolality and urea concentration were measured. RNA was isolated from the whole kidney and real - time PCR was carried out using a LightCycler. Total protein of UTs was assayed from kidney tissue by Western blotting. RESULTS: Mice of both genotypes excreted the urea loaded in ～ 4 h with the same time course. Despite their low baseline, the AQP3 - null mice raised their urine osmolality and urea concentration progressively after the urea load to the values almost equal to those in wild - type mice at 8 h. In contrast, urine non - urea solute concentration did not change. Urine volume fell in the last 4 h to about one - fourth of basal values. The urea load strongly upregulated urea transporter UT - A3 expression in both genotype mice. CONCLUSION: These observations show that lack of AQP3 does not interfere with the ability of the kidney to concentrate urea but impairs its ability to concentrate other solutes. This solute - selective response results from the capacity of AQP3 to transport not only water but also urea, suggesting a novel role for AQP3 in non - urea solute concentration in the urine.
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