Lipid Ion Channels

Abstract

The interpretation electrical phenomena in biomembranes is usually based on the assumption that the experimentally found discrete ion conduction events are due to a particular class of proteins called ion channels while the lipid membrane is considered being an inert electrical insulator. The particular protein structure is thought to be related to ion specificity, specific recognition of drugs by receptors and to macroscopic phenomena as nerve pulse propagation. However, lipid membranes in their chain melting regime are known to be highly permeable to ions, water and small molecules, and are therefore not always inert. In voltage-clamp experiments one finds quantized conduction events through protein-free membranes in their melting regime similar to or even undistinguishable from those attributed to proteins. This constitutes a conceptual problem for the interpretation of electrophysiological data obtained from biological membrane preparations. Here, we review the experimental evidence for lipid ion channels, their properties and the physical chemistry underlying their creation. We introduce into the thermodynamic theory of membrane fluctuations from which the lipid channels originate. Furthermore, we demonstrate how the appearance of lipid channels can be influenced by the alteration of the thermodynamic variables (temperature, pressure, tension, chemical potentials) in a coherent description that is free of parameters. This description leads to pores that display dwell times closely coupled to the fluctuation lifetime via the fluctuation-dissipation theorem. Drugs as anesthetics and neurotransmitters are shown to influence the channel likelihood and their lifetimes in a predictable manner. We also discuss the role of proteins in influencing the likelihood of lipid channel formation.

Review

References in corpus (8)

• The temperature dependence of lipid membrane permeability, its quantized nature, and the influence of anesthetics
• The thermodynamics of general anesthesia
• On the action potential as a propagating density pulse and the role of anesthetics
• Phase state dependent current fluctuations in pure lipid membranes
• The influence of anesthetics, neurotransmitters and antibiotics on the relaxation processes in lipid membranes
• Ion-channel-like behavior in lipid bilayer membranes at the melting transition
• The thermodynamics of lipid ion channel formation in the absence and presence of anesthetics. BLM experiments and simulations
• Defect formation of lytic peptides in lipid membranes and their influence on the thermodynamic properties of the pore environment

Cited by in corpus (16)

• The capacitance and electromechanical coupling of lipid membranes close to transitions. The effect of electrostriction
• A Quantitative Overview of Biophysical Forces Governing Neural Function
• Melting transitions in biomembranes
• Voltage-gated lipid ion channels
• Electrical properties of polar membranes
• Periodic solutions and refractory periods in the soliton theory for nerves and the locust femoral nerve
• Comparing ion conductance recordings of synthetic lipid bilayers with cell membranes containing TRP channels
• Electromechanical coupling of waves in nerve fibres
• The thermodynamic soliton theory of the nervous impulse and possible medical implications
• Phase transitions in biological membranes
• On the excitation of action potentials by protons and its potential implications for cholinergic transmission
• The excitable fluid mosaic
• The mechanical properties of nerves, the size of the action potential, and consequences for the brain
• A physical perspective on lithium therapy
• Lipid ion channels and the role of proteins
• Nonlinear conductance, rectification and mechanosensitive channel formation of lipid membranes