Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom.
PLoS One. 2024 Jul 25;19(7):e0307765. doi: 10.1371/journal.pone.0307765. eCollection 2024.
The existence of temperature gradients within eukaryotic cells has been postulated as a source of natural convection in the cytoplasm, i.e. bulk fluid motion as a result of temperature-difference-induced density gradients. Recent computations have predicted that a temperature differential of ΔT ≈ 1 K between the cell nucleus and the cell membrane could be strong enough to drive significant intracellular material transport. We use numerical computations and theoretical calculations to revisit this problem in order to further understand the impact of temperature gradients on flow generation and advective transport within cells. Surprisingly, our computations yield flows that are an order of magnitude weaker than those obtained previously for the same relative size and position of the nucleus with respect to the cell membrane. To understand this discrepancy, we develop a semi-analytical solution of the convective flow inside a model cell using a bi-spherical coordinate framework, for the case of an axisymmetric cell geometry (i.e. when the displacement of the nucleus from the cell centre is aligned with gravity). We also calculate exact solutions for the flow when the nucleus is located concentrically inside the cell. The results from both theoretical analyses agree with our numerical results, thus providing a robust estimate of the strength of cytoplasmic natural convection and demonstrating that these are much weaker than previously predicted. Finally, we investigate the ability of the aforementioned flows to redistribute solute within a cell. Our calculations reveal that, in all but unrealistic cases, cytoplasmic convection has a negligible contribution toward enhancing the diffusion-dominated mass transfer of cellular material.
真核细胞内存在温度梯度，这被认为是细胞质中自然对流的一个来源，即由于温度差引起的密度梯度导致的整体流体运动。最近的计算预测，细胞核和细胞膜之间的温差 ΔT ≈ 1 K 可能足以驱动显著的细胞内物质运输。为了进一步了解温度梯度对细胞内流动产生和输运的影响，我们使用数值计算和理论计算来重新研究这个问题。令人惊讶的是，我们的计算得出的流动比以前为相同的核相对于细胞膜的相对大小和位置获得的流动弱一个数量级。为了理解这种差异，我们使用双球坐标框架为轴对称细胞几何形状（即当细胞核从细胞中心的位移与重力对齐时）的模型细胞内的对流流动开发了半解析解。我们还计算了当核位于细胞内部同心时的流动的精确解。这两种理论分析的结果都与我们的数值结果一致，从而提供了细胞质自然对流强度的可靠估计，并表明其比以前预测的要弱得多。最后，我们研究了上述流动在细胞内重新分配溶质的能力。我们的计算表明，除了不切实际的情况外，细胞质对流对增强细胞物质的扩散主导的传质几乎没有贡献。
