Tubular lipid membranes pulled from vesicles: Dependence of system equilibrium on lipid bilayer curvature
- PDF / 529,906 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 228 Views
TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Tubular Lipid Membranes Pulled from Vesicles: Dependence of System Equilibrium on Lipid Bilayer Curvature I. Yu. Golushko* and S. B. Rochal Southern Federal University, Rostov-on-Don, 344090 Russia *e-mail: [email protected] Received July 1, 2015
Abstract—Conditions of joint equilibrium and stability are derived for a spherical lipid vesicle and a tubular lipid membrane (TLM) pulled from this vesicle. The obtained equations establish relationships between the geometric and physical characteristics of the system and the external parameters, which have been found to be controllable in recent experiments. In particular, the proposed theory shows that, in addition to the pressure difference between internal and external regions of the system, the variable spontaneous average curvature of the lipid bilayer (forming the TLM) also influences the stability of the lipid tube. The conditions for stability of the cylindrical phase of TLMs after switching off the external force that initially formed the TLM from a vesicle are discussed. The loss of system stability under the action of a small axial force compressing the TLM is considered. DOI: 10.1134/S1063776116010027
1. INTRODUCTION The cell membrane is one of the most important components of a living cell. Membranes play a key role in both the structural organization and functioning of all cells. They separate the cell space from the surrounding medium, participate in most intracellular processes, and connect cells with each other in tissues. Under physiological conditions, most lipid membranes exhibit the properties of a two-dimensional (2D) liquid and can adopt a variety of shapes, from planar to spherical and cylindrical ones [1]. Membranes of the latter type, called tubular lipid membranes (TLMs), reach up to several hundred microns in length with a radius of only a few tens of nanometers [2]. TLMs are involved in most intra- and extracell exchange processes and are found in a number of organelles such as mitochondria, Golgi apparatus, and endoplasmic reticulum [3, 4]. Development of experimental methods have made it possible to simulate such membrane systems under controllable laboratory conditions [2, 5–9]. A rather popular method for preparing and studying TLMs is to mechanically “pull” them from vesicles formed from biological membranes or from synthetic phospholipid membranes [2, 6–9]. This method has much in common with one of the possible TLM formation mechanism in living cells, according to which TLMs are formed by motor proteins moving along microfilaments of the cytoskeleton [5]. In recent years, extensive studies have been devoted to mechanisms of variation in the spontaneous curvature C0 of a lipid bilayer, which ensure the stability of TLMs in the absence of
external forces [8, 10]. In such experiments, it is possible to control not only the tensile force, but also the small pressure difference ΔP = Pin – Pout between the regions inside and outside a membrane, which had been previously ignored conventionally
Data Loading...
