Molecular and functional characterization of the electroneutral Na/HCO3 cotransporter NBCn1 in rat hippocampal neurons
Molecular and functional characterization of the electroneutral Na/HCO3 cotransporter NBCn1 in rat hippocampal neurons
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DOI：
10.1074/jbc.m408646200
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发表时间：
2005-05-06
影响因子：
4.8
通讯作者：
Choi, IY
中科院分区：
文献类型：
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作者：
Cooper, DS;Saxena, NC;Choi, IY
我们研究了存在于大鼠海马神经元中的电中性钠/碳酸氢盐协同转运蛋白（NBCn 1）的分子和电生理特性。通过PCR，在成年神经元中发现了胞质N端结构域缺失123个氨基酸的缺失变体（NBCn 1-E）。在胚胎神经元中检测到先前表征的NBCn 1-B，其不具有缺失。在非洲爪蟾卵母细胞中，NBCn 1-E提高细胞内的pH值在HCO 3的存在下，而不显着影响膜电位。尽管有这种电中性共转运活性，转运蛋白介导的稳态电流使静息电位正移近30 mV。稳态电流的平均反转电位为-21.2 mV，接近静息电位-21.4 mV。当浓度超过10 mM时，当外部Na+浓度增加10倍时，逆转电位移动26 mV。K+、Mg 2+、Ca 2+或Cl-不影响转运蛋白介导的电流活性。在人胚肾细胞中稳定表达NBCn 1-E也诱发了一种内向电流，与假转染对照组相比，该电流使静息电位更加积极。在胚胎海马神经元的原代培养中，NBCn 1蛋白定位于体树突和突触。NBCn 1蛋白与突触后密度蛋白PSD-95部分共定位。单细胞PCR结果显示NBCn 1 mRNA在GABA能神经元和非GABA能神经元均有表达。我们提出，NBCn 1在海马神经元可能会影响神经元的活动，通过调节当地的pH值以及稳态内向电流在突触。
We examined molecular and electrophysiological properties of the electroneutral sodium/bicarbonate cotransporter (NBCn1) that is present in rat hippocampal neurons. By PCR, a deletion variant (NBCn1-E) that lacks 123 amino acids in the cytoplasmic N-terminal domain was found in adult neurons. The previously characterized NBCn1-B, which does not have the deletion, was detected in embryonic neurons. In Xenopus oocytes, NBCn1-E raised the intracellular pH in the presence of HCO3 without significantly affecting the membrane potential. Despite this electroneutral cotransport activity, the transporter mediated a steady-state current that positively shifted the resting potential by almost 30 mV. The mean reversal potential of the steady-state current was - 21.2 mV, close to the resting potential of - 21.4 mV. The reversal potential shifted 26 mV in response to a 10-fold increase of external Na+ for concentrations above 10 mM. The current activity mediated by the transporter was unaffected by K+, Mg2+, Ca2+, or Cl-. Stable expression of NBCn1-E in human embryonic kidney cells also evoked an inward current that shifted the resting potentials more positive compared with the sham-transfected controls. In primary cultures of embryonic hippocampal neurons, the NBCn1 protein was localized in somatodendrites and synapses. NBCn1 protein was partially colocalized with the postsynaptic density protein PSD-95. Single-cell PCR showed that NBCn1 mRNA expression was present in both gamma-aminobutyric acid ( GABA) ergic and non-GABAergic neurons. We propose that NBCn1 in hippocampal neurons may affect neuronal activity by regulating local pH as well as steady-state inward currents at synapses.