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Na+/HCO3-共转运体的电生理学原理

陈历明, 刘梅，刘颖

华中科技大学生命科学与技术学院生物物理学及分子生理学系，分子生物物理学教育部重点实验室，武汉 430074

摘要

离子通道或离子转运体介导的离子跨膜运输是细胞中两种重要的离子跨膜运输方式。与离子通道介导的被动运输不同，离子转运体介导的离子跨膜转运是一种主动运输方式，具有多种独特的生物学特性。本文以Na+/HCO3-共转运体(Na+/HCO3- cotransporter, NBC)为例，对离子转运体的物理化学和电生理学基本原理及其特性进行分析与介绍。从本质上说，离子转运体是一种酶，本文首先从酶促反应的角度，对NBC介导的离子跨膜运输过程进行分析，介绍了离子转运体的化学计量比、表征离子转运效率的转换数及与此相关的离子转运体的运输通量等。本文进一步从热力学的角度对NBC介导Na+和HCO3-跨膜运输的电生理学原理进行了较为详细的分析。通过热力学分析，本文阐释了NBC依据化学计量比决定其离子转运方向的原理。最后，本文对NBC化学计量比的实验测定和化学计量比的生理学意义，即NBC不同工作模式与其在特定组织中的具体生理学过程的关系，进行了讨论。

关键词： 离子转运体; 酸碱平衡; 碳酸氢根转运体; 离子通道; 电生理学; 电压钳; 化学计量比; 转换数

Electrophysiology principles of Na+/HCO3- cotransporters

CHEN Li-Ming, LIU Mei

Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science &； Technology School of Life Science &

Abstract

Ion channels and transporters represent two major types of pathways of transmembrane transport for ions. Distinct from ion channels which conduct passive ionic diffusion, ion transporters mediate active transport of ions. In the perspective of biochemistry, ion transporters are enzymes that catalyze the movement of ions across the plasma membrane. In the present review, we selected the Na+/HCO3- cotransporter (NBC) as an example to analyze the key biochemical and biophysical properties of ion transporters, including stoichiometry, turnover number and transport capacity. Moreover, we provided an analysis of the electrophysiological principles of NBC based on the laws of thermodynamics. Based on the thermodynamical analysis, we showed how the stoichiometry of an NBC determines the direction of its ion transport. Finally, we reviewed the methodology for experimental determination of the stoichiometry of NBC, as well as the physiological significance of the stoichiometry of NBCs in specific tissues.

Key words: bicarbonate transporter; acid-base balance; ion transporter; ion channel; electrophysiology; electrochemistry; voltage clamp; stoichiometry

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引用本文：

陈历明, 刘梅，刘颖. Na+/HCO3-共转运体的电生理学原理[J]. 生理学报 2016; 68 (3): 323-334.

CHEN Li-Ming, LIU Mei. Electrophysiology principles of Na+/HCO3- cotransporters. Acta Physiol Sin 2016; 68 (3): 323-334 (in Chinese with English abstract).