Kowacz Magdalena, Pollack Gerald H
Department of Bioengineering, University of Washington, Box 355061, Seattle, Washington 98195, United States.
ACS Omega. 2020 Aug 11;5(33):21024-21031. doi: 10.1021/acsomega.0c02595. eCollection 2020 Aug 25.
The ionic compositions of the intra- and extracellular environments are distinct from one another, with K being the main cation in the cytosol and Na being the most abundant cation outside of the cell. Specific ions can permeate into and out of the cell at different rates, bringing about uneven distribution of charges and development of negative electric potential inside the cell. Each healthy cell must maintain a specific ion concentration gradient and voltage. To account for these functions, various ionic pumps and channels located within the cell membrane have been invoked. In this work, we use a porous alginate hydrogel as a model gelatinous network representing the plant cell wall or cytoskeleton of the animal cell. We show that the gel barrier is able to maintain a stable separation of ionic solutions of different ionic strengths and chemical compositions without any pumping activity. For the Na/K concentration gradient sustained across the barrier, a negative electric potential develops within the K-rich side. The situation is reminiscent of that in the cell. Furthermore, also the advective flow of water molecules across the gel barrier is restricted, despite the gel's large pores and the osmotic or hydrostatic pressure gradients across it. This feature has important implications for osmoregulation. We propose a mechanism in which charge separation and electric fields developing across the permselective (gel) membrane prevent ion and bulk fluid flows ordinarily driven by chemical and pressure gradients.
细胞内和细胞外环境的离子组成彼此不同，钾是胞质溶胶中的主要阳离子，而钠是细胞外最丰富的阳离子。特定离子能够以不同速率进出细胞，导致电荷分布不均并在细胞内部产生负电势。每个健康细胞都必须维持特定的离子浓度梯度和电压。为实现这些功能，细胞膜内存在各种离子泵和离子通道。在这项工作中，我们使用多孔藻酸盐水凝胶作为一种模型凝胶网络，它代表植物细胞壁或动物细胞的细胞骨架。我们表明，这种凝胶屏障能够在没有任何泵浦活动的情况下，维持不同离子强度和化学成分的离子溶液的稳定分离。对于跨越屏障维持的钠/钾浓度梯度，富含钾的一侧会产生负电势。这种情况让人联想到细胞内的情形。此外，尽管凝胶具有大孔以及跨凝胶的渗透压或静水压力梯度，但水分子通过凝胶屏障的平流也受到限制。这一特性对渗透调节具有重要意义。我们提出一种机制，其中跨选择性渗透（凝胶）膜产生的电荷分离和电场会阻止通常由化学和压力梯度驱动的离子和大量流体流动。
