Stabilization of pores in lipid bilayers by anisotropic inclusions

Pores in lipid bilayers are usually not stable; they shrink because of the highly unfavorable line tension of the pore rim. Even in the presence of charged lipids or certain additives such as detergents or isotropic membrane inclusions, membrane pores are generally not expected to be energetically stabilized. We present a theoretical model that predicts the existence of stable pores in a lipid membrane, induced by the presence of anisotropic inclusions. Our model is based on a phenomenological free energy expression that involves three contributions: the energy associated with the line tension of the pore in the absence of inclusions, the electrostatic energy of the pore for charged membranes, and the interaction energy between the inclusions and the host membrane. We show that the optimal pore size is governed by the shape of the anisotropic inclusions: saddle-like inclusions favor small pores, whereas more wedgelike inclusions give rise to larger pore sizes. We discuss possible applications of our model and use it to explain the observed dependency of the pore radius in the membrane of red blood cell ghosts on the ionic strength of the surrounding solution.