Surface Deformation During an Action Potential in Pearled Cells

TL;DR

This study investigates the mechanical surface deformations in pearled Chara cells during action potentials, revealing larger shape changes and modeling the mechanics through surface tension, bending rigidity, and pressure differences.

Contribution

It introduces a curvature-based model to quantify mechanical parameters during cell excitation, advancing understanding of surface deformation mechanisms in plant cells.

Findings

Pearling instability leads to larger deformations during excitation.

A curvature model with three parameters fits experimental shape changes.

Mechanical parameters vary during action potential, as quantified by the model.

Abstract

Electric pulses in biological cells (action potentials) have been reported to be accompanied by a propagating cell-surface deformation with a nano-scale amplitude. Typically, this cell surface is covered by external layers of polymer material (extracellular matrix, cell wall material etc.). It was recently demonstrated in excitable plant cells (Chara Braunii) that the rigid external layer (cell wall) hinders the underlying deformation. When the cell membrane was separated from the cell wall by osmosis, a mechanical deformation, in the micrometer range, was observed upon excitation of the cell. The underlying mechanism of this mechanical pulse has up to date remained elusive. Herein we report that Chara cells can undergo a pearling instability, and when the pearled fragments were excited even larger and more regular cell shape changes were observed (about 10 to 100 um in amplitude). These transient cellular deformations were captured by a curvature model that is based on three parameters: surface tension, bending rigidity and pressure difference across the surface. In this paper these parameters are extracted by curve-fitting to the experimental cellular shapes at rest and during excitation. This is a necessary step to identify the mechanical parameters that change during an action potential.