Action potential as a contributing factor in axonal transport: a numerical study

Despite various studies on axonal mechanics in recent years, the mechanisms and factors contributing to axonal transport are still not fully understood. In this study, the possible role of action potential (AP) propagation through neurites in axonal transport was explored by utilizing underlying physical principles through numerical simulation. A fluid-structure interaction model was used to simulate the physical behavior of the axon as action potential waves propagate. The axon and its membrane were modeled as a fluid-filled cylinder with elastic walls, where the action potential acts as a moving radial load on the axon. Utilizing computational fluid dynamics simulation and accounting for forces induced by the action potential led to the emergence of an intercellular fluid flow inside the axon, which was subsequently incorporated into current models of axonal transport in the literature. The convective intercellular fluid flow induced by the action potential acts as a mechanism for axonal transport, with velocities ranging from 2 to 17 mm per day, which is consistent with previously reported ranges for the slow axonal transport component. Additionally, by incorporating the effect of convective flow, it was shown that unidirectional transport, coupled with convective transport, can successfully describe the movement of larger cargos against their concentration gradients. The results demonstrated that for the squid giant axon and hippocampal neurites, the displacement pulse propagates almost simultaneously with the AP. Analyzing the interaction between action potential and axonal transport can lead to a better understanding of these phenomena.