In eukaryotic cells, the phospholipid cardiolipin (CL) is a crucial component that influences the function and organization of the mitochondrial inner membrane. In this study, we examined its potential role in passive proton transmembrane flux using unilamellar vesicles composed of natural egg phosphatidylcholine (PC) alone or with the inclusion of 18 or 34 mol% CL. A membrane potential was induced by a potassium gradient, and oxonol VI dye was used to monitor membrane potential dissipation resulting from proton transmembrane efflux. Increasing the CL content led to a net increase in proton efflux, which was also dependent on the magnitude of the membrane potential. The same increase in proton efflux was measured in the presence of the equally negatively charged phosphatidylglycerol (PG), indicating that the charge of CL plays a more important role than its structure in this mechanism. When varying the proton membrane permeability (PH) using the protonophore CCCP, we observed that unlike PC liposomes, where a small amount of CCCP was sufficient to achieve maximum flux, a significantly larger amount of protonophore was required in the presence of CL. Conversely, increasing the buffer capacity increased proton flux, indicating that proton availability, rather than membrane permeability, may be the limiting factor for proton leak. Our findings demonstrated that a higher proton content associated with the membrane was correlated with an increasing leak in the presence of CL. Additionally, smaller liposome diameters appeared to favor proton leak. Taken together, our results suggest that the presence of negatively charged CL in a membrane traps protons and increases their leakage, potentially in a manner dependent on membrane curvature. We discuss possible mechanisms and implications of these findings for mitochondrial respiration function.

中文翻译：

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心磷脂在质子跨膜通量和定位中的作用。


在真核细胞中，磷脂心磷脂 （CL） 是影响线粒体内膜功能和组织的关键成分。在这项研究中，我们使用由天然鸡蛋磷脂酰胆碱 （PC） 单独或包含 18 或 34 mol% CL 组成的单层囊泡检查了它在被动质子跨膜通量中的潜在作用。由钾梯度诱导膜电位，并使用 oxonol VI 染料监测质子跨膜外排引起的膜电位耗散。增加 CL 含量导致质子外排净增加，这也取决于膜电位的大小。在同样带负电荷的磷脂酰甘油 （PG） 存在下测量质子外排的相同增加，表明 CL 的电荷在该机制中起着比其结构更重要的作用。当使用质子泳 CCCP 改变质子膜通透性 （PH） 时，我们观察到与 PC 脂质体不同，在 PC 脂质体中，少量的 CCCP 足以达到最大通量，而在 CL 存在的情况下需要明显更多的质子泡。相反，增加缓冲容量会增加质子通量，表明质子可用性，而不是膜通透性， 可能是质子泄漏的限制因素。我们的研究结果表明，在 CL 存在下，与膜相关的较高质子含量与渗漏增加相关。此外，较小的脂质体直径似乎有利于质子渗漏。综上所述，我们的结果表明，膜中存在带负电荷的 CL 会捕获质子并增加其泄漏，可能以某种方式取决于膜曲率。 我们讨论了这些发现对线粒体呼吸功能的可能机制和影响。