We modeled the relaxation dynamics of (lipid) vesicles upon osmotic upshift, taking into account volume variation, chemical reaction kinetics, and passive transport across the membrane. We focused on the relaxation kinetics upon addition of impermeable osmolytes such as KCl and membrane-permeable solutes such as weak acids. We studied the effect of the most relevant physical parameters on the dynamic behavior of the system, as well as on the relaxation rates. We observe that 1) the dynamic complexity of the relaxation kinetics depends on the number of permeable species; 2) the permeability coefficients (P) and the weak acid strength (pKa-values) determine the dynamic behavior of the system; 3) the vesicle size does not affect the dynamics, but only the relaxation rates of the system; and 4) heterogeneities in the vesicle size provoke stretching of the relaxation curves. The model was successfully benchmarked for determining permeability coefficients by fitting of our experimental relaxation curves and by comparison of the data with literature values (in this issue of Biophysical Journal). To describe the dynamics of yeast cells upon osmotic upshift, we extended the model to account for turgor pressure and nonosmotic volume.

中文翻译：

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渗透压升高时囊泡动力学的物理化学模型


我们模拟了渗透压升高时（脂质）囊泡的松弛动力学，考虑了体积变化、化学反应动力学和跨膜被动运输。我们重点研究了添加不可渗透的渗透剂（例如 KCl）和膜渗透性溶质（例如弱酸）时的弛豫动力学。我们研究了最相关的物理参数对系统动态行为以及弛豫率的影响。我们观察到：1）弛豫动力学的动态复杂性取决于可渗透物质的数量； 2）渗透系数（P）和弱酸强度（pKa值）决定系统的动态行为； 3）囊泡大小不影响动力学，只影响系统的弛豫率； 4) 囊泡大小的异质性引起弛豫曲线的拉伸。通过拟合我们的实验松弛曲线并将数据与文献值（在本期《生物物理学杂志》中）进行比较，该模型成功地确定了渗透系数的基准。为了描述渗透压升高时酵母细胞的动力学，我们扩展了模型以考虑膨胀压和非渗透体积。