Maex Reinoud
Biocomputation Research Group, School of Physics, Engineering and Computer Science, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK.
Membranes (Basel). 2023 Feb 7;13(2):206. doi: 10.3390/membranes13020206.
Neurons spend most of their energy building ion gradients across the cell membrane. During energy deprivation the neurons swell, and the concomitant mixing of their ions is commonly assumed to lead toward a Donnan equilibrium, at which the concentration gradients of all permeant ion species have the same Nernst potential. This Donnan equilibrium, however, is not isotonic, as the total concentration of solute will be greater inside than outside the neurons. The present theoretical paper, in contrast, proposes that neurons follow a path along which they swell quasi-isotonically by co-transporting water and ions. The final neuronal volume on the path is taken that at which the concentration of impermeant anions in the shrinking extracellular space equals that inside the swelling neurons. At this final state, which is also a Donnan equilibrium, all permeant ions can mix completely, and their Nernst potentials vanish. This final state is isotonic and electro-neutral, as are all intermediate states along this path. The path is in principle reversible, and maximizes the work of mixing.
神经元将大部分能量用于在细胞膜上建立离子梯度。在能量剥夺期间，神经元会肿胀，通常认为其离子的随之混合会趋向于唐南平衡，此时所有可渗透离子种类的浓度梯度具有相同的能斯特电位。然而，这种唐南平衡并非等渗的，因为神经元内部溶质的总浓度将高于外部。相比之下，这篇理论论文提出，神经元遵循一条通过共转运水和离子而近似等渗肿胀的路径。该路径上的最终神经元体积是取收缩的细胞外空间中不可渗透阴离子的浓度等于肿胀神经元内部浓度时的体积。在这个最终状态，它也是一种唐南平衡，所有可渗透离子可以完全混合，并且它们的能斯特电位消失。这个最终状态以及这条路径上的所有中间状态都是等渗且电中性的。这条路径原则上是可逆的，并且使混合功最大化。
