Department of Cell and Molecular Biology, University of Gothenburg, Medicinaregatan 9C, SE-413 90 Göteborg, Sweden.
Integr Biol (Camb). 2011 Nov;3(11):1120-6. doi: 10.1039/c1ib00027f. Epub 2011 Oct 19.
Cell volume is a biophysical property, which is of great importance for quantitative characterisations of biological processes, such as osmotic adaptation. It also is a crucial parameter in the most common type of mathematical description of cellular behaviour-ordinary differential equation (ODE) models, e.g. the integrative model of the osmotic stress response in baker's yeast (E. Klipp, B. Nordlander, R. Kruger, P. Gennemark and S. Hohmann, Nat. Biotechnol., 2005, 23, 975-982). Until recently only rough estimates of this value were available. In this study we measured the mean volume of more than 300 individual yeast cells (Saccharomyces cerevisiae). We quantitatively characterised the dependence between the relative cell volume and the concentration of osmoticum in the cell surrounding. We also followed the recovery of the cellular volume over time, as well as the influence of increased external osmolarity on the nuclear volume. We found that cell shrinkage caused by shifts in the external osmolarity is proportional to the stress intensity only up to 1000 mM NaCl. At this concentration the yeast cells shrink to approximately 55% of their unstressed volume and this volume is maintained even in the case of further osmolarity increase. We observed that returning to the initial, unstressed volume takes more than 45 minutes for stress concentrations exceeding 100 mM NaCl and that only cells treated with the latter concentration are able to fully regain their initial size within the course of the experiment. We postulate that the cytoplasm plays a protective role for the nucleus by buffering the changes in volume caused by external osmolarity shifts. In conclusion, we quantitatively characterised the dynamics of cell volume changes caused by hyperosmotic stress, providing an accurate description of a biophysical cell property, which is crucial for precise mathematical simulations of cellular processes.
细胞体积是一种生物物理性质，对于定量描述生物学过程（如渗透适应）非常重要。它也是最常见的细胞行为数学描述类型——常微分方程（ODE）模型的关键参数，例如面包酵母渗透胁迫反应的综合模型（E. Klipp、B. Nordlander、R. Kruger、P. Gennemark 和 S. Hohmann，Nat. Biotechnol.，2005，23，975-982）。直到最近，人们只能得到这个值的粗略估计。在这项研究中，我们测量了 300 多个单个酵母细胞（酿酒酵母）的平均体积。我们定量描述了相对细胞体积与细胞周围渗透压之间的关系。我们还跟踪了细胞体积随时间的恢复情况，以及外部渗透压增加对核体积的影响。我们发现，由于外部渗透压的变化导致的细胞收缩与压力强度成正比，直到 1000mM NaCl 为止。在这个浓度下，酵母细胞收缩到其未受胁迫体积的约 55%，并且即使渗透压进一步增加，这个体积也保持不变。我们观察到，在超过 100mM NaCl 的应激浓度下，恢复到初始未受胁迫的体积需要超过 45 分钟，并且只有在处理后者浓度的情况下，细胞才能在实验过程中完全恢复其初始大小。我们假设细胞质通过缓冲由外部渗透压变化引起的体积变化来保护核。总之，我们定量描述了由高渗胁迫引起的细胞体积变化的动力学，为细胞过程的精确数学模拟提供了对生物物理细胞性质的准确描述。
