Effect of expressing the water channel aquaporin-1 on the CO2 permeability of Xenopus oocytes
Effect of expressing the water channel aquaporin-1 on the CO2 permeability of Xenopus oocytes
复制标题
DOI：
10.1152/ajpcell.1998.274.2.c543
复制
发表时间：
1998-02-01
影响因子：
5.5
通讯作者：
Boron, WF
中科院分区：
文献类型：
--
作者：
Nakhoul, NL;Davis, BA;Boron, WF
人们普遍认为，二氧化碳等气体通过溶解在膜脂中而穿过细胞膜。管道或气孔在天然气运输中的作用从未被证明。在这里，我们问水通道水通道蛋白-1(AQP1)的表达是否增强了非洲爪哇卵母细胞的二氧化碳通透性。我们通过注射AQP1cRNA在非洲爪哇卵母细胞中表达了AQP1，并用微电极监测了在胞外溶液中添加1.5%CO2/10 mMHCO3-或从胞外溶液中去除CO2所产生的胞内pH(pH(I))的变化。卵母细胞通常具有无法检测到的低水平碳酸氢酶(CA)，这消除了二氧化碳水合反应作为限速步骤的作用。我们发现，在低CA卵母细胞中，表达水通道蛋白1与注入水相比，对CO_2诱导的pH(I)变化没有明显的影响：添加CO_2使pH(I)在对照卵母细胞中以平均11.3×10~(-4)pH单位/S的速度下降，在表达水通道蛋白1的卵母细胞中以13.3×10~(-4)pH单位/S的平均初始速率下降。当我们向卵母细胞注入水，并在几天后注入CA，这些水/CA卵母细胞的pH(I)变化比水注入卵母细胞快四倍以上(酸化速率，53×10~(-4)pH单位/S)。乙氧唑胺(Etx；10 mU M)可显著减缓pH(I)的变化(16.5×10~(-4)pH单位/S)。当我们向卵母细胞注射AQP1CRNA和CA时，这些AQP1/CA卵母细胞的pH(I)变化比水/CA卵母细胞快40%(75×10~(-4)pH单位/S)，ETX显著降低了这一速率(14.7×10~(-4)pH单位/S)。因此，在CA存在的情况下，AQP1的表达显著增加了卵母细胞膜的CO2通透性。可能的解释包括：1)AQP1的表达改变了细胞膜的脂质组成，2)AQP1的表达导致了天然气体通道的过度表达，和/或3)AQP1起到了二氧化碳渗透通道的作用。即使AQP1应该调节二氧化碳通量，这种二氧化碳移动是否在数量上是重要的仍有待确定。
It is generally accepted that gases such as CO2 cross cell membranes by dissolving in the membrane lipid. No role for channels or pores in gas transport has ever been demonstrated. Here we ask whether expression of the water channel aquaporin-1 (AQP1) enhances the CO2 permeability of Xenopus oocytes. We expressed AQP1 in Xenopus oocytes by injecting AQP1 cRNA, and we assessed CO2 permeability by using microelectrodes to monitor the changes in intracellular pH (pH(i)) produced by adding 1.5% CO2/10 mM HCO3- to (or removing it from) the extracellular solution. Oocytes normally have an undetectably low level of carbonic anhydrase (CA), which eliminates the CO2 hydration reaction as a rate-limiting step. We found that expressing AQP1 (vs. injecting water) had no measurable effect on the rate of CO2-induced pH(i) changes in such low-CA oocytes: adding CO2 caused pH(i) to fall at a mean initial rate of 11.3 x 10(-4) pH units/s in control oocytes and 13.3 x 10(-4) pH units/s in oocytes expressing AQP1. When we injected oocytes with water, and a few days later with CA, the CO2-induced pH(i) changes in these water/CA oocytes were more than fourfold faster than in water-injected oocytes (acidification rate, 53 x 10(-4) pH units/s). Ethoxzolamide (ETX; 10 mu M), a membrane-permeant CA inhibitor, greatly slowed the pH(i) changes (16.5 x 10(-4) pH units/s). When we injected oocytes with AQP1 cRNA and then CA, the CO2-induced pH(i) changes in these AQP1/CA oocytes were similar to 40% faster than in the water/CA oocytes (75 x 10(-4) pH units/s), and ETX reduced the rates substantially (14.7 x 10(-4) pH units/s). Thus, in the presence of CA, AQP1 expression significantly increases the CO2 permeability of oocyte membranes. Possible explanations include 1) AQP1 expression alters the lipid composition of the cell membrane, 2) AQP1 expression causes overexpression of a native gas channel, and/or 3) AQP1 acts as a channel through which CO2 can permeate. Even if AQP1 should mediate a CO2 flux, it would remain to be determined whether this CO2 movement is quantitatively important.