Substrate specificity of the electrogenic sodium/bicarbonate cotransporter NBCe1-A (SLC4A4, variant A) from humans and rabbits
Substrate specificity of the electrogenic sodium/bicarbonate cotransporter NBCe1-A (SLC4A4, variant A) from humans and rabbits
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DOI：
10.1152/ajprenal.00612.2012
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发表时间：
2013-04-01
影响因子：
4.2
通讯作者：
Parker, Mark D.
中科院分区：
文献类型：
--
作者：
Lee, Seong-Ki;Boron, Walter F.;Parker, Mark D.
Lee SK, Boron WF, Parker MD.电致钠/碳酸氢盐共转运体NBCe1-A （SLC4A4，变体A）的底物特异性。[J] .中国生物医学工程学报，2013,31(4):893 - 899。首次发表于2013年1月14日；doi: 10.1152 / ajprenal.00612.2012。在近端小管细胞的基底外膜中，NBCe1-A （SLC4A4，变体A）的Na+:HCO3-化学计量明显为1:3，有助于从肾小球滤液中回收HCO3-，从而防止全身酸中毒。其他人报道nbce1样活性在人、兔和大鼠肾脏制剂中受到锂、亚硫酸盐、草酸盐和缬氨酸的实质性影响。这些数据可以作为NBCe1-A中存在不同Na+和CO32-结合位点的证据，支持1 Na+:1 HCO3-:1 CO32-的模型。在这里，我们通过在爪蟾卵母细胞中表达人或兔NBCe1-A克隆来重新验证这些发现。在卵母细胞中，NBCe1-A表现出1:2的化学计量，可以在五种热力学等效的运输模式中进行操作：1)Na+ + 2 HCO3-的共运输，2)Na+ + CO32-的共运输，3)NaCO3-的运输，4)Na+ + HCO3-交换H+，或5)HCO3-激活的Na+交换2h +。与肾制剂中nbce1样活性的行为相反，我们发现克隆的NBCe1-A仅受Li+的轻微刺激，完全不受亚硫酸盐或草酸盐的影响，仅受盐碱的微弱抑制。这些负面数据并不唯一地支持上述五个模型中的任何一个。此外，我们发现NBCe1-A介导少量不依赖Na+的NO3-转运，并且NBCe1-A在一定程度上受到细胞外苯甲胺的抑制。我们认为肾制剂中nbce1样活性的特征受到尚未确定的肾脏因素的影响。因此，NBCe1的实际离子底物仍有待鉴定。
Lee SK, Boron WF, Parker MD. Substrate specificity of the electrogenic sodium/bicarbonate cotransporter NBCe1-A (SLC4A4, variant A) from humans and rabbits. Am J Physiol Renal Physiol 304: F883-F899, 2013. First published January 14, 2013; doi:10.1152/ajprenal.00612.2012.-In the basolateral membrane of proximal-tubule cells, NBCe1-A (SLC4A4, variant A), operating with an apparent Na+ :HCO3- stoichiometry of 1:3, contributes to the reclamation of HCO3- from the glomerular filtrate, thereby preventing whole body acidosis. Others have reported that NBCe1-like activity in human, rabbit, and rat renal preparations is substantially influenced by lithium, sulfite, oxalate, and harmaline. These data were taken as evidence for the presence of distinct Na+ and CO32- binding sites in NBCe1-A, favoring a model of 1 Na+ : 1 HCO3- :1 CO32-. Here, we reexamine these findings by expressing human or rabbit NBCe1-A clones in Xenopus oocytes. In oocytes, NBCe1-A exhibits a 1: 2 stoichiometry and could operate in one of five thermodynamically equivalent transport modes: 1) cotransport of Na+ + 2 HCO3-, 2) cotransport of Na+ + CO32-, 3) transport of NaCO3-, 4) exchange of Na+ + HCO3- for H+, or 5) HCO3--activated exchange of Na+ for 2 H+. In contrast to the behavior of NBCe1-like activity in renal preparations, we find that cloned NBCe1-A is only slightly stimulated by Li+, not at all influenced by sulfite or oxalate, and only weakly inhibited by harmaline. These negative data do not uniquely support any of the five models above. In addition, we find that NBCe1-A mediates a small amount of Na+-independent NO3- transport and that NBCe1-A is somewhat inhibited by extracellular benzamil. We suggest that the features of NBCe1-like activity in renal preparations are influenced by yet-to-be-identified renal factors. Thus the actual ionic substrates of NBCe1 remain to be identified.