Effros R M, Mason G R, Hukkanen J, Silverman P
Harbor-UCLA Medical Center, Torrance 90509.
J Appl Physiol (1985). 1989 Feb;66(2):906-19. doi: 10.1152/jappl.1989.66.2.906.
The hypothesis that fluid reabsorption from the air spaces is mediated at least in part by active transport of Na+ was investigated in six sets of experiments conducted in isolated fluid-filled rat lungs. Fluid reabsorption was monitored by following the changes in the air space concentration of labeled albumin. We found that incorporation of bicarbonate rather than a nonvolatile buffer (N-2-hydroxy-ethylpiperazine-N'-2-ethanesulfonic acid) in the air space solution more than doubled the rate of fluid reabsorption. Addition of 10(-4) M amiloride to the air space solution reduced the rate of fluid reabsorption over a 2-h experiment from 1.2 +/- 0.1 to 0.7 +/- 0.1 ml and decreased reabsorption of both labeled and unlabeled Na+ from the air spaces. To show that Na+ could be reabsorbed from the air spaces even if the concentrations of Na+ in the perfusate increased above those in the air space, mannitol (150 mM) was added to the perfusate and air space solutions and the concentrations of Na+ and Cl- were reduced to 90 and 60 mM, respectively. Mannitol diffuses across the pulmonary epithelium very slowly, and it osmotically restrained the movement of water out of the air spaces. Na+ concentrations in the perfusate increased by 10 +/- 2 mM, but concentrations in the air space remained unchanged. Despite an increasingly unfavorable concentration gradient for Na+, 0.2 mmol Na+ and 0.6 ml water were reabsorbed from the air spaces in 2 h. Ouabain (10(-4) M) did not appear to slow fluid reabsorption in the presence of mannitol, but it reduced K+ secretion into the air spaces and increased K+ appearance in the perfusate in a manner consistent with inhibition of Na+-K+-adenosinetriphosphatase at the basolateral surface of the epithelial cells. Fluid reabsorption was not altered when the lungs were exposed to a hypotonic solution (185 mM), but secretion of K+ into the air spaces was accelerated and K+ was lost from the perfusate. These experiments are consistent with active Na+ transport from the air spaces.
在六组对分离的充满液体的大鼠肺进行的实验中，研究了肺泡腔液体重吸收至少部分由Na⁺主动转运介导的假说。通过追踪标记白蛋白在肺泡腔浓度的变化来监测液体重吸收。我们发现，在肺泡腔溶液中加入碳酸氢盐而非非挥发性缓冲剂（N-2-羟乙基哌嗪-N'-2-乙磺酸），可使液体重吸收率增加一倍多。在2小时的实验中，向肺泡腔溶液中加入10⁻⁴M氨氯吡脒，使液体重吸收率从1.2±0.1降至0.7±0.1ml，并减少了肺泡腔中标记和未标记Na⁺的重吸收。为了表明即使灌注液中Na⁺浓度高于肺泡腔中的浓度，Na⁺仍可从肺泡腔重吸收，向灌注液和肺泡腔溶液中加入甘露醇（150mM），并将Na⁺和Cl⁻浓度分别降至90和60mM。甘露醇跨肺上皮扩散非常缓慢，它通过渗透作用抑制水从肺泡腔流出。灌注液中Na⁺浓度增加了10±2mM，但肺泡腔中的浓度保持不变。尽管Na⁺的浓度梯度越来越不利于其转运，但在2小时内仍有0.
