Prasad G V, Coury L A, Finn F, Zeidel M L
Laboratory of Epithelial Cell Biology, Renal Electrolyte Division, and Protein Purification Laboratory, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
J Biol Chem. 1998 Dec 11;273(50):33123-6. doi: 10.1074/jbc.273.50.33123.
Biological membranes provide selective barriers to a number of molecules and gases. However, the factors that affect permeability to gases remain unclear because of the difficulty of accurately measuring gas movements. To determine the roles of lipid composition and the aquaporin 1 (AQP1) water channel in altering CO2 flux across membranes, we developed a fluorometric assay to measure CO2 entry into vesicles. Maximal CO2 flux was approximately 1000-fold above control values with 0.5 mg/ml carbonic anhydrase. Unilamellar phospholipid vesicles of varying composition gave widely varying water permeabilities but similar CO2 permeabilities at 25 degreesC. When AQP1 purified from human red blood cells was reconstituted into proteoliposomes, however, it increased water and CO2 permeabilities markedly. Both increases were abolished with HgCl2, and the mercurial inhibition was reversible with beta-mercaptoethanol. We conclude that unlike water and small nonelectrolytes, CO2 permeation is not significantly altered by lipid bilayer composition or fluidity. AQP1 clearly serves to increase CO2 permeation, likely through the water pore; under certain circumstances, gas permeation through membranes is protein-mediated.
生物膜对许多分子和气体具有选择性屏障作用。然而，由于准确测量气体运动存在困难，影响气体渗透性的因素仍不明确。为了确定脂质组成和水通道蛋白1（AQP1）水通道在改变跨膜二氧化碳通量中的作用，我们开发了一种荧光测定法来测量二氧化碳进入囊泡的情况。在含有0.5mg/ml碳酸酐酶的情况下，最大二氧化碳通量比对照值高出约1000倍。不同组成的单层磷脂囊泡具有广泛不同的水渗透性，但在25℃时二氧化碳渗透性相似。然而，当从人红细胞中纯化的AQP1重组到蛋白脂质体中时，它显著增加了水和二氧化碳的渗透性。这两种增加都被HgCl2消除，并且汞抑制作用可被β-巯基乙醇逆转。我们得出结论，与水和小的非电解质不同，脂质双层组成或流动性不会显著改变二氧化碳的渗透。AQP1显然有助于增加二氧化碳的渗透，可能是通过水孔；在某些情况下，气体通过膜的渗透是由蛋白质介导的。
