Schnermann J, Chou C L, Ma T, Traynor T, Knepper M A, Verkman A S
Department of Physiology, University of Michigan Medical School, Ann Arbor, MI 48109-0622, USA.
Proc Natl Acad Sci U S A. 1998 Aug 4;95(16):9660-4. doi: 10.1073/pnas.95.16.9660.
To investigate the role of aquaporin-1 (AQP1) water channels in proximal tubule function, in vitro proximal tubule microperfusion and in vivo micropuncture measurements were done on AQP1 knockout mice. The knockout mice were generated by targeted gene disruption and found previously to be unable to concentrate their urine in response to water deprivation. Unanesthetized knockout mice consumed 2.8-fold more fluid than wild-type mice and had lower urine osmolality (505 +/- 40 vs. 1081 +/- 68 milliosmolar). Transepithelial osmotic water permeability (Pf) in isolated microperfused S2 segments of proximal tubule from AQP1 knockout [-/-] mice was 0.033 +/- 0.005 cm/s (SE, n = 6 mice, 37 degreesC), much lower than that of 0.15 +/- 0.03 cm/s (n = 8) in tubules from wild-type [+/+] mice (P < 0.01). In the presence of isosmolar luminal perfusate and bath solutions, spontaneous fluid absorption rates (nl/min/mm tubule length) were 0.31 +/- 0.12 (-/-, n = 5) and 0.64 +/- 0.15 (+/+, n = 8). As determined by free-flow micropuncture, the ratios of tubular fluid-to-plasma concentrations of an impermeant marker TF/P in end proximal tubule fluid were 1.36 +/- 0. 05 (-/-, n = 8 mice [53 tubules]) and 1.95 +/- 0.09 (+/+, n = 7 mice [40 tubules]) (P < 0.001), corresponding to 26 +/- 3% [-/-] and 48 +/- 2% [+/+] absorption of the filtered fluid load. In collections of distal tubule fluid, TF/P were 2.8 +/- 0.3 [-/-] and 4.4 +/- 0.5 [+/+], corresponding to 62 +/- 4% [-/-] and 76 +/- 3% [+/+] absorption (P < 0.02). These data indicate that AQP1 deletion in mice results in decreased transepithelial proximal tubule water permeability and defective fluid absorption. Thus, the high water permeability in proximal tubule of wild-type mice is primarily transcellular, mediated by AQP1 water channels, and required for efficient near-isosmolar fluid absorption.
为研究水通道蛋白-1（AQP1）水通道在近端小管功能中的作用，对AQP1基因敲除小鼠进行了体外近端小管微灌注和体内微穿刺测量。基因敲除小鼠通过靶向基因破坏产生，先前发现其在缺水时无法浓缩尿液。未麻醉的基因敲除小鼠的液体摄入量比野生型小鼠多2.8倍，尿渗透压较低（505±40对1081±68毫渗量）。来自AQP1基因敲除[-/-]小鼠的近端小管分离微灌注S2段的跨上皮渗透水通透性（Pf）为0.033±0.005厘米/秒（标准误，n = 6只小鼠，37℃），远低于野生型[+/+]小鼠小管的0.15±0.03厘米/秒（n = 8）（P < 0.01）。在等渗管腔灌注液和浴液存在的情况下，自发液体吸收率（纳升/分钟/毫米小管长度）分别为0.31±0.12（-/-，n = 5）和0.64±0.15（+/+，n = 8）。通过自由流微穿刺测定，近端小管末端液体中不可渗透标记物的管腔液与血浆浓度之比TF/P分别为1.36±0.05（-/-，n = 8只小鼠[53个小管]）和1.95±0.09（+/+，n = 7只小鼠[40个小管]）（P < 0.001），分别对应于滤过液负荷的26±3%[-/-]和48±2%[+/+]的重吸收。在远端小管液收集物中，TF/P分别为2.8±0.3[-/-]和4.4±0.5[+/+]，分别对应于62±4%[-/-]和76±3%[+/+]的重吸收（P < 0.02）。这些数据表明，小鼠中AQP1的缺失导致近端小管跨上皮水通透性降低和液体重吸收缺陷。因此，野生型小鼠近端小管的高水通透性主要是跨细胞的，由AQP1水通道介导，是有效近等渗液体重吸收所必需的。
