Mechanism of bicarbonate exit across basolateral membrane of rabbit proximal straight tubule.
Mechanism of bicarbonate exit across basolateral membrane of rabbit proximal straight tubule.
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碳酸氢根穿过兔近端直小管基底外侧膜的排出机制。
DOI：
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发表时间：
1987
影响因子：
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通讯作者：
J. Takeuchi
中科院分区：
文献类型：
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作者：
S. Sasaki;T. Shiigai;N. Yoshiyama;J. Takeuchi
为了阐明HCO3-（或相关碱）跨基底外侧膜运输的机制，体外灌注兔近端直管，并用双管离子选择微电极测量细胞内pH （pHi）和Na+活性（aiNa）。在恒定PCO2下，将浴液HCO3-从25 mM降低到5 mM，基底侧膜电位（Vbl）去极化，并降低pHi。在溶液中加入1 mM的4-乙酰氨基-4′-异硫氰基二苯乙烯-2,2′-二磺酸（SITS）可以抑制这些变化。用胆碱完全替代浴Na+也能去极化Vbl和降低pHi，这些变化也被sit抑制。当HCO3-降低时，观察到aiNa的减少。综上所述，这些发现表明HCO3-存在于带Na+和负电荷的基底外侧膜中。电化学驱动力的计算表明，HCO3-/Na+的化学计量量必须大于2才能维持HCO3-的外排。异乙硫酸盐去极化Vbl逐渐完全取代Cl-， pHi略有增加，表明存在与Cl（-）相关的HCO3-退出机制。在没有Cl-的情况下，降低HCO3-诱导的pHi下降速率略有降低（20%）。因此，与Cl（-）相关的HCO3-运输相对于总基底侧HCO3-排出的重要性较小。因此，这些数据表明，大部分HCO3-通过HCO3-/ HCO3-的流变共转运机制离开基底侧膜，HCO3-/Na+的化学计量量大于2。
To clarify the mechanism(s) of HCO3- (or related base) transport across the basolateral membrane, rabbit proximal straight tubules were perfused in vitro, and intracellular pH (pHi) and Na+ activity (aiNa) were measured by double-barreled ion-selective microelectrodes. Lowering bath HCO3- from 25 to 5 mM at constant PCO2 depolarized basolateral membrane potential (Vbl), and reduced pHi. Most of these changes were inhibited by adding 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to the bath. Total replacement of bath Na+ with choline also depolarized Vbl and reduced pHi, and these changes were also inhibited by SITS. Reduction in aiNa was observed when bath HCO3- was lowered. Taken together, these findings suggest that HCO3- exists the basolateral membrane with Na+ and negative charge. Calculation of the electrochemical driving forces suggests that the stoichiometry of HCO3-/Na+ must be larger than two for maintaining HCO3- efflux. Total replacement of bath Cl- with isethionate depolarized Vbl gradually and increased pHi slightly, implying the existence of a Cl(-)-related HCO3- exit mechanism. The rate of decrease in pHi induced by lowering bath HCO3- was slightly reduced (20%) by the absence of bath Cl-. Therefore, the importance of Cl(-)-related HCO3- transport is small relative to total basolateral HCO3- exit. Accordingly, these data suggest that most of HCO3- exits the basolateral membrane through the rheogenic Na+/HCO3- cotransport mechanism with a stoichiometry of HCO3-/Na+ of more than two.