Elastic, Electrostatic and Electrokinetic Processes Contributing to Membrane Curvature - Membrane Shape as a Memory Element

Abstract

The curvature of cellular membranes is controlled by a variety of physical mechanisms, whose relative importance and interplay is still to be worked out. Moreover the notion that the membrane curvature controls a variety of biological processes, and that it also may be an important factor in regulating vesicular secretion, is gaining ground. In this study we evaluate what mechanical forces, such as may be generated by the cytoskeleton, are needed to generate required membrane deflection and deformation. We also consider the role the electrical forces play in the membrane deformation, and which may be present under physiological conditions. Membrane deformation is evaluated using a coupled system of linear elastic equations and electrostatic-electrokinetic (Poisson-Nernst-Planck) equations. If the fixed charges on the membrane are asymmetrical the electrostatic forces generated can produce significant bending of the membrane. Even when the distribution of fixed charges on both sides of the membrane is symmetrical the membrane bending occurs, if the intracellular and extracellular ion concentrations are different. Finally, upon removal of the forces (mechanical or electrical) that induce the membrane curvature the membrane relaxes toward the original configuration with a time course that depends on the membrane properties. The shape of the membrane can thus serve as a memory element regulating various biological processes including those of vesicular secretion.