Chang W, Loretz C A
Department of Biological Sciences, State University of New York, Buffalo 14260.
Am J Physiol. 1993 Jul;265(1 Pt 2):R66-75. doi: 10.1152/ajpregu.1993.265.1.R66.
The columnar cell epithelium of the euryhaline goby (Gillichthys mirabilis) urinary bladder actively absorbs NaCl from the lumen, thereby driving water transport and reducing water loss to the hypertonic external environment. Transcellular transport of Cl- involves apical membrane entry via Na(+)-coupled cotransport driven by the Na+ electrochemical gradient and subsequent basolateral membrane exit. An anion channel in the basolateral cell membrane of columnar epithelial cells was identified using patch-clamp technique. This channel may be one avenue for basolateral Cl- exit from the urinary bladder columnar cell. Single-channel conductance (Gc) of channels in excised, inside-out membrane patches was approximately 75 pS in symmetrical solutions containing 140 mM Cl-. The channel was selective to Cl- over other anions [Cl- > 2-(N-morpholino)ethanesulfonic acid (MES) > F- approximately Br- approximately I- > NO3- approximately SO4(2-)). Channel activity, expressed as the open probability (Po), was voltage dependent in the physiological range of membrane potential, with membrane depolarization increasing Po. Decreasing the pH of the solution bathing the cytoplasmic face of the membrane patch over the range 8.4-6.0 reduced Po. There was no effect of pH on either Gc or ionic selectivity. Radiochloride flux technique was also applied to intact columnar epithelial cell sheets to relate anion channel activity to macroscopic transcellular transport. Serosal exposure to the anion channel blocker diphenylamine-2-carboxylic acid (DPC, 30 microM to 3 mM) reduced and abolished transcellular radiochloride fluxes and net Cl- absorption across short-circuited tissues in a dose-dependent fashion. DPC addition (10 microM to 1 mM) to the solution bathing the cytoplasmic face of excised, inside-out membrane patches reduced Po in a dose-dependent manner and had no effect on Gc. These parallel findings of DPC blockade on intact epithelia and on single anion channels support the notion that this anion channel is a basolateral membrane component of the pathway for Cl- movement in transcellular Cl- absorption.
广盐性虾虎鱼（奇异吉利虾虎鱼）膀胱的柱状上皮细胞能从管腔中主动吸收氯化钠，从而驱动水分运输，并减少向高渗外部环境的水分流失。氯离子的跨细胞运输包括通过由钠离子电化学梯度驱动的钠耦联共转运进入顶端膜，以及随后从基底外侧膜排出。利用膜片钳技术在柱状上皮细胞的基底外侧细胞膜中鉴定出了一种阴离子通道。该通道可能是氯离子从膀胱柱状细胞基底外侧排出的一条途径。在含有140 mM氯离子的对称溶液中，切除的内面向外膜片上通道的单通道电导（Gc）约为75 pS。该通道对氯离子的选择性高于其他阴离子[氯离子＞2-（N-吗啉代）乙磺酸（MES）＞氟离子≈溴离子≈碘离子＞硝酸根离子≈硫酸根离子（2-）]。通道活性以开放概率（Po）表示，在膜电位的生理范围内依赖于电压，膜去极化会增加Po。将膜片细胞质面一侧的溶液pH值在8.4至6.0范围内降低会降低Po。pH值对Gc或离子选择性均无影响。放射性氯离子通量技术也应用于完整的柱状上皮细胞片，以将阴离子通道活性与宏观跨细胞运输联系起来。浆膜侧暴露于阴离子通道阻滞剂二苯胺-2-羧酸（DPC，30 microM至3 mM）会以剂量依赖的方式降低并消除跨细胞放射性氯离子通量以及短路组织中的净氯离子吸收。向切除的内面向外膜片细胞质面一侧的溶液中添加DPC（10 microM至1 mM）会以剂量依赖的方式降低Po，且对Gc无影响。DPC对完整上皮细胞和单个阴离子通道的阻断作用的这些平行发现支持了这样一种观点，即该阴离子通道是跨细胞氯离子吸收中氯离子移动途径的基底外侧膜成分。
