Analysis of cardiac mitochondrial Na+-Ca2+ exchanger kinetics with a biophysical model of mitochondrial Ca2+ handing suggests a 3: 1 stoichiometry
Analysis of cardiac mitochondrial Na+-Ca2+ exchanger kinetics with a biophysical model of mitochondrial Ca2+ handing suggests a 3: 1 stoichiometry
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DOI：
10.1113/jphysiol.2008.151977
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发表时间：
2008-07-01
影响因子：
5.5
通讯作者：
Beard, Daniel A.
中科院分区：
文献类型：
--
作者：
Dash, Ranjan K.;Beard, Daniel A.
钙离子是一种关键离子，介导细胞质和线粒体之间的信号通路，调节线粒体能量代谢。为了获得对线粒体Ca2+调控的定量生物物理理解，我们通过将线粒体Ca2+单转运体（CU）、Na+-Ca2+交换器（NCE）和Na+-H+交换器（NHE）的动力学模型整合到现有的线粒体氧化磷酸化计算模型中，建立了线粒体Ca2+处理和生物能量学的热力学平衡模型。基于纯化线粒体中测量的通量率的独立数据集，开发了CU、NCE和NHE的动力学通量表达式，并分别进行了参数化。虽然现有数据支持心脏和肝脏线粒体中CU总体活性的广泛可能值，但即使在最高估计值下，通过CU的Ca2+电流对线粒体膜电位没有显着影响。然后，该集成模型用于分析线粒体CU和NCE控制的线粒体Ca2+动态和稳态的其他数据。我们用两种不同的模型（一种是2:1的化学计量，另一种是3:1的NCE化学计量）分析了从兔心脏纯化的呼吸线粒体中添加不同水平的Na+ （CU被阻断）的无基质[Ca2+]的时间过程数据，支持了NCE的化学计量为3:1的电生假设。通过模拟另一个独立的数据集来进一步验证这一假设，该数据集关于纯化大鼠心脏呼吸线粒体中游离基质[Ca2+]的稳态变化，表明只有1:1的化学计量模型预测与数据一致。基于这些分析，我们认为线粒体NCE具有电致性，其化学计量比为3:1。
Calcium is a key ion and is known to mediate signalling pathways between cytosol and mitochondria and modulate mitochondrial energy metabolism. To gain a quantitative, biophysical understanding of mitochondrial Ca2+ regulation, we developed a thermodynamically balanced model of mitochondrial Ca2+ handling and bioenergetics by integrating kinetic models of mitochondrial Ca2+ uniporter (CU), Na+-Ca2+ exchanger (NCE), and Na+-H+ exchanger (NHE) into an existing computational model of mitochondrial oxidative phosphorylation. Kinetic flux expressions for the CU, NCE and NHE were developed and individually parameterized based on independent data sets on flux rates measured in purified mitochondria. While available data support a wide range of possible values for the overall activity of the CU in cardiac and liver mitochondria, even at the highest estimated values, the Ca2+ current through the CU does not have a significant effect on mitochondrial membrane potential. This integrated model was then used to analyse additional data on the dynamics and steady-states of mitochondrial Ca2+ governed by mitochondrial CU and NCE. Our analysis of the data on the time course of matrix free [Ca2+] in respiring mitochondria purified from rabbit heart with addition of different levels of Na+ to the external buffer medium (with the CU blocked) with two separate models - one with a 2: 1 stoichiometry and the other with a 3: 1 stoichiometry for the NCE - supports the hypothesis that the NCE is electrogenic with a stoichiometry of 3: 1. This hypothesis was further tested by simulating an additional independent data set on the steady-state variations of matrix free [Ca2+] with respect to the variations in external free [Ca2+] in purified respiring mitochondria from rat heart to show that only the 3: 1 stoichiometry model predictions are consistent with the data. Based on these analyses, it is concluded that the mitochondrial NCE is electrogenic with a stoichiometry of 3: 1.