Charged cell membrane in electrolyte

TL;DR

This paper investigates how surface charge affects the mechanical properties of cell membranes, revealing that membranes are always under tension due to electric fields, contradicting previous capacitor models, with implications for pore formation.

Contribution

It provides a new understanding of membrane tension influenced by surface charge and electrolyte conditions, challenging the capacitor analogy and proposing experimental tests.

Findings

Membranes are always under tension regardless of surface charge sign.

Electric field effects dominate over charge magnitude due to Debye length considerations.

Surface charge influences pore compression and stretching depending on pore size relative to Debye radius.

Abstract

An effect of membrane surface charge on mechanical properties of the phospholipid bilayer membrane and pores formation is considered. It is shown that the outer and inner surfaces of the phospholipid membrane is always subject to tension, regardless of magnitude and sign of the charges on its surface. This is due to the fact that the Debye length of the extracellular and intracellular electrolyte is always much smaller than the thickness of the membrane, and accordingly the electric field on the outer surface of the membrane is always much larger than the field inside the membrane. This result contradicts the generally accepted notion that a charged phospholipid membrane is similar to a charged capacitor in a dielectric medium and it is always subject to compression. Phospholipid bilayer membrane will be subject to compression only in a very weak electrolyte (~1mM/L), when Debye length is larger than the membrane thickness. It is also shown that the membrane surface charges lead to pore compression when the pore radius is larger than the Debye radius and to the stretching in the opposite case. Difference in the coefficients of surface and edge tension of phospholipid cell membranes can be explained by taking into account the cell membrane surface charge. Simple experiments are proposed to test the influence of the cell membrane surface charge on its mechanical properties.