Passive permeation of small amphiphilic molecules of dimethyl sulfoxide (DMSO) through a phospholipid membrane. Water is shown in blue, lipid molecules in green, and DMSO molecules in yellow-red-cyan.

Pore formation coupled to ion transport through lipid membranes as induced by transmembrane ionic charge imbalance. Water is shown in red-white, Na ions in yellow, and Cl ions in green. The lipid membrane is not shown (black space). Excess of Na ions is on the left-hand side.
A.A. Gurtovenko, I. Vattulainen, J. Am. Chem. Soc. 127, 17570 (2005).

Water-defect-mediated permeation of a potassium ion across a lipid membrane without actual pore formation. Water is shown in red-white and the potassium ion in yellow. The lipid membrane is not shown (black space). Excess of K ions is on the left-hand side.
A.A. Gurtovenko, I. Vattulainen, Biophys. J. 92, 1878 (2007).

Pore formation induced by transmembrane ionic charge imbalance, pore-mediated ion leakage, and membrane resealing. Water is shown in red-white, choline groups of lipid head groups in blue, phosphate and glycerol groups in cyan, K ions in orange, and Cl ions in green. Nonpolar acyl chains of lipids are not shown (black space). Excess of K ions is on the left-hand side.
A.A. Gurtovenko, I. Vattulainen, Biophys. J. 92, 1878 (2007).