Ionic mechanism of Na+-HCO3- cotransport in rabbit renal basolateral membrane vesicles.
Ionic mechanism of Na+-HCO3- cotransport in rabbit renal basolateral membrane vesicles.
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DOI：
10.1016/s0021-9258(18)51463-0
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发表时间：
1989-11
期刊：
影响因子：
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通讯作者：
M. Soleimani;P. Aronson
中科院分区：
文献类型：
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作者：
M. Soleimani;P. Aronson
HCO 3 −穿过近端小管细胞的基底外侧膜，是通过每Na+3 eq碱的产电共转运发生的。我们已经使用从兔肾皮质分离的基底外侧膜囊泡，以确定通过这一途径运输的离子种类。采用不同pH和pCO 2的介质来评估HCO 3 −和CO 32 −对22 Na转运的独立影响。当[HCO 3-]恒定时[CO 32-]增加时，Na+吸收被刺激，表明存在CO 32-的转运位点。在存在HCO 3 −的情况下，Na+内流被向内的SO 32 −梯度刺激超过3倍。SO 32 −刺激的Na+内流对二苯乙烯敏感，证实它通过Na+-HCO 3 −共转运系统发生。Na+-SO 32 −共转运被证明并发现具有1：1的化学计量。在[HCO 3 −]不变的情况下，增加[CO 32 −]会减少SO 32 −对Na+内流的刺激，这表明SO 32 −和CO 32 −在一个共同的二价阴离子位点上存在竞争。测试的其他二价阴离子，例如SO 42-、草酸根2-和HPO 4（2-），在该位点不发生相互作用。SO 32 −对Na+内流的刺激完全依赖于HCO 3 −（-），并随着[HCO 3 −]的增加而增加，表明存在单独的HCO 3 −位点。最后，我们测试了Na+是否通过离子对形成与CO 32 −相互作用或结合到不同的位点。Na+在与CO 32 −形成离子对时的亲和力低于Li+，但在Na+-HCO 3 −共转运系统中，Na+的亲和力比Li+高5倍以上。此外，当它的抑制作为[Na+]的函数进行了研究，harvestin被发现是一个竞争性抑制剂的Na+流入，表明存在一个独特的阳离子位点。我们的数据与一个模型是一致的，在该模型中，碱通过近端小管细胞基底外侧膜的转运是通过CO 32-、HCO 3-和Na+在不同位点上的1：1：1共转运进行的。
The exit of HCO3−across the basolateral membrane of the proximal tubule cell occurs via the electrogenic cotransport of 3 eq of base per Na+. We have used basolateral membrane vesicles isolated from rabbit renal cortex to identify the ionic species transported via this pathway. Media of varying pH and pCO2 were employed to evaluate the independent effects of HCO3−and CO32−on 22Na transport. Na+ uptake was stimulated when [CO32−] was increased at constant [HCO3−], indicating the existence of a transport site for CO32−. In the presence of HCO3−, Na+ influx was stimulated more than 3-fold by an inward SO32−gradient. SO32−-stimulated Na+ influx was stilbene-sensitive, confirming that it occurs via the Na+-HCO3−cotransport system. Na+-SO32−cotransport was demonstrated and found to have a 1:1 stoichiometry. Increasing [CO32−] at constant [HCO3−] reduced the stimulation of Na+ influx by SO32−, suggesting competition between SO32−and CO32−at a common divalent anion site. Additional divalent anions that were tested, such as SO42−, oxalate2-, and HPO4(2-), did not interact at this site. SO32−stimulation of Na+ influx was absolutely HCO3−(-)dependent and was increased as a function of [HCO3−], indicating the presence of a separate HCO3−site. Lastly, we tested whether Na+ interacts via ion pair formation with CO32−or binds to a distinct site. Na+, which has lower affinity than Li+ for ion pair formation with CO32−, was found to have > 5-fold higher affinity than Li+for the Na+-HCO3−cotransport system. Moreover, when its inhibition was studied as a function of [Na+], harmaline was found to be a competitive inhibitor of Na+ influx, indicating the existence of a distinct cation site. Our data are compatible with a model in which base transport across the basolateral membrane of the proximal tubule cell takes place via 1:1:1 cotransport of CO32−, HCO3−, and Na+on distinct sites.