ROLE OF ACTIVE POTASSIUM-TRANSPORT IN THE REGULATION OF CYTOPLASMIC PH BY NONANIMAL CELLS
ROLE OF ACTIVE POTASSIUM-TRANSPORT IN THE REGULATION OF CYTOPLASMIC PH BY NONANIMAL CELLS
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DOI：
10.1073/pnas.84.9.2737
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发表时间：
1987-05-01
影响因子：
11.1
通讯作者：
SLAYMAN, CL
中科院分区：
文献类型：
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作者：
BLATT, MR;SLAYMAN, CL
脉孢菌中的高亲和性钾吸收通过与质子共输而发生[Km（表观）= 15 μ M，pH 5.8]，其中大的向内梯度（约0.5 μ M）为质子的共输。400 mV）由质膜的H+-挤压ATP酶产生。两个转运系统并行运行，产生K+与细胞质H+的1：1净交换。由于这种交换可以在细胞质pH（pHi）调节中发挥作用，因此在酸胁迫期间检查了K+-H+同向转运体和H+泵的协调功能。通过注射和暴露于细胞外渗透性弱酸来施加细胞质酸负荷。多管微电极被用来监测膜电位（Vm），pHi，和电流-电压（I-V）特性的细胞。H+泵和K+-H+同向转运体的行为分别通过将全膜I-V曲线拟合到脉孢菌膜的明确动力学模型和通过从在外部存在5-200 μ M K+的情况下获得的I-V曲线中减去在不存在的情况下获得的I-V曲线来解析。质子泵加速几乎与细胞质H+浓度成比例，但从施加的酸负荷pHi恢复依赖于微摩尔K+外。通过共转运体的钾输入导致细胞质根据化学计量（1：1）K+/H+交换的可测量的碱化。钾运输在低pH值下加速，但其方式与其固有的电压敏感性和Vm变化一致，Vm变化是由泵的H+挤出速率增加引起的。因此，对酸胁迫的主要反应取决于H+泵，但K+运输引入了一个重要的动力学“阀”，可以调节净H+输出。
High-affinity potassium uptake in Neurospora occurs by symport with protons [Km (apparent) = 15 .mu.M at pH 5.8], for which a large inward gradient (.apprxeq. 400 mV) is generated by the H+-extruding ATPase of the plasma membrane. Operating in parallel, the two transport systems yield a net 1:1 exchange of K+ for cytoplasmic H+. Since this exchange could play a role in cytoplasmic pH (pHi) regulation, the coordinated functioning of the K+-H+ symport and H+ pump has been examined during acid stress. Cytoplasmic acid loads were imposed by injection and by exposure to to extracellular permeant weak acid. Multibarrelled microelectrodes were used to monitor membrane potential (Vm), pHi, and the current-voltage (I-V) characteristics of the cells. The behaviors of the H+ pump and K+-H+ symport were resolved, respectively, by fitting whole membrane I-V curves to an explicit kinetic model of the Neurospora membrane and by subtracting I-V curves obtained in the absence from those obtained in the presence of 5-200 .mu.M K+ outside. Proton pumping accelerates nearly in proportion with the cytoplasmic H+ concentration, but pHi recovery from imposed acid loads is dependent on micromolar K+ outside. Potassium import via the symport leads to a measurable alkalinization of the cytoplasm in accordance with stoichiometric (1:1) K+/H+ exchange. Potassium transport is accelerated at low pHi, but in a manner consistent with its inherent voltage sensitivity and changes in Vm resulting from an increased rate of H+ extrusion by the pump. The primary response to acid stress thus rests with the H+ pump, but K+ transport introduces an essential kinetic "valve" that can regulate net H+ export.