Cuppoletti J, Baker A M, Malinowska D H
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0576.
Am J Physiol. 1993 Jun;264(6 Pt 1):C1609-18. doi: 10.1152/ajpcell.1993.264.6.C1609.
HCl secretion across mammalian gastric parietal cell apical membrane may involve Cl- channels. H(+)-K(+)-ATPase-containing membranes isolated from gastric mucosa of histamine-stimulated rabbits were fused to planar lipid bilayers. Channels were recorded with symmetric 800 mM CsCl solutions, pH 7.4. A linear current-voltage (I-V) relationship was obtained, and conductance was 28 +/- 1 pS at 800 mM CsCl. Conductance was 6.9 +/- 2 pS at 150 mM CsCl. Reversal potential was +22 mV with a fivefold cis-trans CsCl concentration gradient, indicating that the channel was anion selective with a discrimination ratio of 6:1 for Cl- over Cs+. Anion selectivity of the channel was I- > Cl- > or = Br- > NO3-, and gluconate was impermeant. Channels obtained at pH 7.4 persisted when pH of medium bathing the trans side of the bilayer (pHtrans) was reduced to pH 3, without a change in conductance, linearity of I-V relationship, or ion selectivity. In contrast, asymmetric reduction of pH of medium bathing the cis side of the bilayer from 7.4 to 3 always resulted in loss of channel activity. At pH 7.4, open probability (Po) of the channel was voltage dependent, i.e., predominantly open at +80 mV but mainly closed at -80 mV. In contrast, with low pHtrans, channel Po at -80 mV was increased 3.5-fold. The Cl- channel was Ca2+ indifferent. In absence of ionophores, ion selectivity for support of H(+)-K(+)-ATPase activity and H+ transport was consistent with that exhibited by the channel and could be limited by substitution with NO3-, whereas maximal H(+)-K(+)-ATPase activity was indifferent to anion present, demonstrating that anion transport can be rate limiting. Cl- channels with similar characteristics (conductance, linear I-V relationship, and ion selectivity) were also present in H(+)-K(+)-ATPase-containing vesicles isolated from resting (cimetidine-treated) gastric mucosa, exhibiting at -80 mV a pH-independent approximately 3.5-fold lower Po than stimulated vesicle channels. At -80 mV, reduction of pHtrans increased Po of both resting and stimulated Cl- channels by five- to sixfold. Changing membrane potential from 0 to -80 mV across stimulated vesicles increased Cl- channel activity an additional 10-fold.(ABSTRACT TRUNCATED AT 400 WORDS)
哺乳动物胃壁细胞顶端膜上的盐酸分泌可能涉及氯离子通道。从组胺刺激的家兔胃黏膜中分离出含有H(+)-K(+)-ATP酶的膜，并将其与平面脂质双层融合。在pH 7.4的对称800 mM氯化铯溶液中记录通道电流。得到了线性电流-电压（I-V）关系，在800 mM氯化铯时电导为28±1 pS。在150 mM氯化铯时电导为6.9±2 pS。在顺式-反式氯化铯浓度梯度为5倍时，反转电位为+22 mV，表明该通道对阴离子具有选择性，对氯离子与铯离子的辨别率为6:1。该通道的阴离子选择性为I-＞Cl-≥Br-＞NO3-，葡萄糖酸盐不能通透。当双层膜反侧的浴液pH（pHtrans）降至pH 3时，在pH 7.4时获得的通道仍然存在，电导、I-V关系的线性度或离子选择性均无变化。相反，将双层膜顺侧的浴液pH从7.4不对称地降至3总是导致通道活性丧失。在pH 7.4时，通道的开放概率（Po）依赖于电压，即在+80 mV时主要开放，而在-80 mV时主要关闭。相反，在低pHtrans时，-80 mV时的通道Po增加了3.5倍。该氯离子通道对钙离子不敏感。在没有离子载体的情况下，支持H(+)-K(+)-ATP酶活性和氢离子转运的离子选择性与通道表现出的一致，并且可能受到用NO3-替代的限制，而最大H(+)-K(+)-ATP酶活性对存在的阴离子不敏感，表明阴离子转运可能是限速因素。从静息（西咪替丁处理）胃黏膜中分离出的含有H(+)-K(+)-ATP酶的囊泡中也存在具有相似特性（电导、线性I-V关系和离子选择性）的氯离子通道，在-80 mV时，其pH非依赖性的Po比受刺激的囊泡通道低约3.5倍。在-80 mV时，降低pHtrans使静息和受刺激的氯离子通道的Po增加了5至6倍。将受刺激囊泡的膜电位从0改变为-80 mV，使氯离子通道活性额外增加了10倍。（摘要截短至400字）
