Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlarska 5, 83334 Bratislava, Slovak Republic.
Eur Biophys J. 2013 Sep;42(9):709-20. doi: 10.1007/s00249-013-0920-2. Epub 2013 Aug 1.
Physiological and pathological functions of mitochondria are highly dependent on the properties and regulation of mitochondrial ion channels. There is still no clear understanding of the molecular identity, regulation, and properties of anion mitochondrial channels. The inner membrane anion channel (IMAC) was assumed to be equivalent to mitochondrial centum picosiemens (mCS). However, the different properties of IMAC and mCS channels challenges this opinion. In our study, we characterized the single-channel anion selectivity and pH regulation of chloride channels from purified cardiac mitochondria. We observed that channel conductance decreased in the order: Cl⁻ > Br⁻ > I⁻ > chlorate ≈ formate > acetate, and that gluconate did not permeate under control conditions. The selectivity sequence was Br⁻ ≥ chlorate ≥ I⁻ ≥ Cl⁻ ≥ formate ≈ acetate. Measurement of the concentration dependence of chloride conductance revealed altered channel gating kinetics, which was demonstrated by prolonged mean open time value with increasing chloride concentration. The observed mitochondrial chloride channels were in many respects similar to those of mCS, but not those of IMAC. Surprisingly, we observed that acidic pH increased channel conductance and that an increase of pH from 7.4 to 8.5 reduced it. The gluconate current appeared and gradually increased when pH decreased from pH 7.0 to 5.6. Our results indicate that pH regulates the channel pore diameter in such a way that dilation increases with more acidic pH. We assume this newly observed pH-dependent anion channel property may be involved in pH regulation of anion distribution in different mitochondrial compartments.
线粒体的生理和病理功能高度依赖于线粒体离子通道的特性和调节。目前对于阴离子线粒体通道的分子身份、调节和特性仍没有明确的认识。人们曾假设内膜阴离子通道（IMAC）等同于线粒体毫西门子（mCS）。然而，IMAC 和 mCS 通道的不同特性对这一观点提出了挑战。在我们的研究中，我们对纯化的心脏线粒体中的氯离子通道的单通道阴离子选择性和 pH 调节进行了表征。我们观察到通道电导按以下顺序降低：Cl⁻ > Br⁻ > I⁻ > 氯酸根 ≈ 甲酸盐 > 乙酸盐，而在对照条件下，葡萄糖酸盐不能渗透。选择性序列为 Br⁻ ≥ 氯酸根 ≥ I⁻ ≥ Cl⁻ ≥ 甲酸盐 ≈ 乙酸盐。氯离子电导的浓度依赖性测量揭示了改变的通道门控动力学，这表现为随着氯离子浓度的增加，平均开放时间值延长。观察到的线粒体氯离子通道在许多方面与 mCS 相似，但与 IMAC 不同。令人惊讶的是，我们观察到酸性 pH 增加了通道电导，而 pH 从 7.4 增加到 8.5 则降低了电导。当 pH 从 7.0 降低到 5.6 时，葡萄糖酸盐电流出现并逐渐增加。我们的结果表明，pH 通过使通道孔径扩大的方式调节通道，随着 pH 变得更酸性，通道孔径增大。我们假设这种新观察到的 pH 依赖性阴离子通道特性可能参与不同线粒体隔室中阴离子分布的 pH 调节。
