Numerical Study of Pressure Response to Action Potential by Water Permeation With Ion Transports

While the permeation mechanism of solute (e.g., ions and glucose) through biological membrane has been studied extensively, the mechanical role of water transport in intracellular phenomena has not received much attention. In the present study, to investigate the effect of water permeation on the intracellular pressure response, a novel permeation flux model through a biological membrane is developed by incorporating the coupling permeabilities (between water and ion fluxes) as the water-ion interaction in the ion channels. The proposed model is applied to a two-dimensional permeation problem of water and ions in a closed cell separated by a thin membrane. The permeation flux model reproduces the typical time response of intracellular pressure to action potentials with reasonable agreement with experimental results in the literature, indicating that the pressure response can be characterized by the following three parameters: water permeability, the mass ratio of water and ion, and the ratio of the permeation fluxes of water and ion. In particular, the permeation flux ratio plays an essential role in intracellular phenomena; depending on the value of the permeation flux ratio, the time lag between the action potential and the pressure response is 0.1 times smaller than that expected by the previous researchers, indicating that water transport associated with ions may trigger a pressure response. This study demonstrates the importance of water permeation in intracellular mechanical response through coupling of the fluid motion and electric fields.