Abdulnour-Nakhoul Solange, Nakhoul Nazih L, Caymaz-Bor Canan, Orlando Roy C
Department of Medicine, Tulane University School of Medicine, and Veterans Administration Medical Center, New Orleans, Louisiana 70112-2699, USA.
Am J Physiol Gastrointest Liver Physiol. 2002 Apr;282(4):G663-75. doi: 10.1152/ajpgi.00085.2001.
We investigated Cl(-) transport pathways in the apical and basolateral membranes of rabbit esophageal epithelial cells (EEC) using conventional and ion-selective microelectrodes. Intact sections of esophageal epithelium were mounted serosal or luminal side up in a modified Ussing chamber, where transepithelial potential difference and transepithelial resistance could be determined. Microelectrodes were used to measure intracellular Cl(-) activity (a), basolateral or apical membrane potentials (V(mBL) or V(mC)), and the voltage divider ratio. When a basal cell was impaled, V(mBL) was -73 +/- 4.3 mV and a(i)(Cl) was 16.4 +/- 2.1 mM, which were similar in presence or absence of bicarbonate. Removal of serosal Cl(-) caused a transient depolarization of V(mBL) and a decrease in a(i)(Cl) of 6.5 +/- 0.9 mM. The depolarization and the rate of decrease of a(i)(Cl) were inhibited by approximately 60% in the presence of the Cl(-)-channel blocker flufenamate. Serosal bumetanide significantly decreased the rate of change of a(i)(Cl) on removal and readdition of serosal Cl(-). When a luminal cell was impaled, V(mC) was -65 +/- 3.6 mV and a was 16.3 +/- 2.2 mM. Removal of luminal Cl(-) depolarized V(mC) and decreased a by only 2.5 +/- 0.9 mM. Subsequent removal of Cl(-) from the serosal bath decreased a(i)(Cl) in the luminal cell by an additional 6.4 +/- 1.0 mM. A plot of V(mBL) measurements vs. log a(i)(Cl)/log a(o)(Cl) (a(o)(Cl) is the activity of Cl(-) in a luminal or serosal bath) yielded a straight line [slope (S) = 67.8 mV/decade of change in a(i)(Cl)/a(o)(Cl)]. In contrast, V(mC) correlated very poorly with log a/a (S = 18.9 mV/decade of change in a/a). These results indicate that 1) in rabbit EEC, a(i)(Cl) is higher than equilibrium across apical and basolateral membranes, and this process is independent of bicarbonate; 2) the basolateral cell membrane possesses a conductive Cl(-) pathway sensitive to flufenamate; and 3) the apical membrane has limited permeability to Cl(-), which is consistent with the limited capacity for transepithelial Cl(-) transport. Transport of Cl(-) at the basolateral membrane is likely the dominant pathway for regulation of intracellular Cl(-).
我们使用传统微电极和离子选择性微电极研究了兔食管上皮细胞（EEC）顶膜和基底外侧膜中的氯离子（Cl⁻）转运途径。将食管上皮的完整切片以浆膜面或腔面向上的方式安装在改良的Ussing室中，在此可测定跨上皮电位差和跨上皮电阻。使用微电极测量细胞内Cl⁻活性（a）、基底外侧或顶膜电位（V(mBL)或V(mC)）以及分压器比率。当刺入一个基底细胞时，V(mBL)为-73±4.3 mV，a(i)(Cl)为16.4±2.1 mM，在有无碳酸氢盐存在时相似。去除浆膜侧的Cl⁻导致V(mBL)短暂去极化，a(i)(Cl)降低了-6.5±0.9 mM。在Cl⁻通道阻滞剂氟芬那酸存在的情况下，去极化和a(i)(Cl)的降低速率被抑制了约60%。浆膜侧布美他尼显著降低了去除和重新添加浆膜侧Cl⁻时a(i)(Cl)的变化速率。当刺入一个腔面细胞时，V(mC)为-65±3.6 mV，a为16.3±2.2 mM。去除腔面的Cl⁻使V(mC)去极化，a仅降低了-2.5±0.9 mM。随后从浆膜浴中去除Cl⁻使腔面细胞中的a(i)(Cl)又额外降低了-6.4±1.0 mM。V(mBL)测量值与log a(i)(Cl)/log a(o)(Cl)（a(o)(Cl)是腔面或浆膜浴中Cl⁻的活性）的关系图得到一条直线[斜率（S）= 67.8 mV/（a(i)(Cl)/a(o)(Cl)每变化一个数量级）]。相比之下，V(mC)与log a/a的相关性非常差（S = 18.9 mV/（a/a每变化一个数量级））。这些结果表明：1）在兔EEC中，a(i)(Cl)高于顶膜和基底外侧膜的平衡值，且该过程与碳酸氢盐无关；2）基底外侧细胞膜具有对氟芬那酸敏感的传导性Cl⁻途径；3）顶膜对Cl⁻的通透性有限，这与跨上皮Cl⁻转运能力有限一致。基底外侧膜上的Cl⁻转运可能是调节细胞内Cl⁻的主要途径。
