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Journal ArticleDOI

Surface Charge and the Conductance of Phospholipid Membranes

TL;DR: The large changes in conductance observed upon varying the surface charge density and the ionic strength agree with those predicted by the Gouy-Chapman theory for an aqueous diffuse double layer.
Abstract: Bilayer membranes, formed from various phospholipids, were studied to assess the influence of the charge of the polar head groups on the membrane conductance mediated by neutral „carriers” of cations and anions. The surface charge of an amphoteric lipid, phosphatidyl ethanolamine, was altered by varying the pH, and the surface charge of several lipids was screened by increasing the ionic strength of the solution with impermeant monovalent and divalent electrolytes. The surface charge should be a key parameter in defining the membrane conductance for a variety of permeation mechanisms; conductance measurements in the presence of carriers may be used to estimate the potential difference, due to surface charge, between the interior of the bilayer and the bulk aqueous phase. The large changes in conductance observed upon varying the surface charge density and the ionic strength agree with those predicted by the Gouy-Chapman theory for an aqueous diffuse double layer. Explicit expressions for the dependence of the membrane conductance on the concentrations of the carrier, the permeant ion, the surface charge density, and the ionic strength are presented.
Citations
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Book ChapterDOI
TL;DR: The chapter describes hydrophobic adsorption of charged molecules to bilayer membranes, the electro static potential produced by molecular dipoles at membrane-solution interfaces, and the electrostatic boundary potentialproduced by charges located in the interior of the membrane, a few angstroms from the interface.
Abstract: Publisher Summary This chapter discusses electrostatic potentials at membrane solution interfaces. Lipids in the membranes of all cells and subcellular organelles are arranged in the form of a bilayer with the hydrocarbon tails sequestered away from the water and the polar head groups exposed to the aqueous environment. About 10%–20% of the lipids in the membranes of many cells and organelles bear a net negative charge, whereas positively charged lipids are extremely rare. The concentration of monovalent cations at the surface of the bilayer will be an order of magnitude higher than the concentration of these ions in the bulk aqueous phase. The surface potential produced by charged lipids is dependent on the salt concentration in the bulk aqueous phase and a seminal paper. The absence of proteins, polysaccharides, and other macromolecules present in biological membranes can be considered an advantage to test how well the theory of the diffuse double layer describes the electrostatic potential produced by charges on lipids. The chapter describes hydrophobic adsorption of charged molecules to bilayer membranes, the electrostatic potential produced by molecular dipoles at membrane-solution interfaces, and the electrostatic boundary potential produced by charges located in the interior of the membrane, a few angstroms from the interface. Few examples of the possible biological significance of these electrostatic surface potentials are also described.

789 citations

Journal ArticleDOI
TL;DR: It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20–26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.
Abstract: Phospholipid bilayer membranes were bathed in a decimolar solution of monovalent ions, and the conductance produced by neutral carriers of these monovalent cations and anions was used to assess the electric potential at the surface of the membrane. When the bilayers were formed from a neutral lipid, phosphatidylethanolamine, the addition of alkaline earth cations produced no detectable surface potential, indicating that little or no binding occurs to the polar head group with these ions. When the bilayers were formed from a negatively charged lipid, phosphatidylserine, the addition of Sr and Ba decreased the magnitude of the surface potential as predicted by the theory of the diffuse double layer. In particular, the potential decreased 27 mv for a 10-fold increase in concentration in the millimolar-decimolar range. A 10-fold increase in the Ca or Mg concentration also produced a 27 mv decrease in potential in this region, which was again due to screening, but it was necessary to invoke some specific binding to account for the observation that these cations were effective at a lower concentration than Ba or Sr. It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20–26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.

600 citations

BookDOI
01 Jan 1986
TL;DR: This chapter discusses the physical nature of Planar Bilayer Membrane Electrostatics and the Shapes of Channel Proteins, as well as analysis and Chemical Modification of Bacterial Porins.
Abstract: I Basics- 1 The Physical Nature of Planar Bilayer Membranes- 2 Ion Channel Electrostatics and the Shapes of Channel Proteins- 3 Superoxide Dismutase as a Model Ion Channel- 4 Single-Channel Enzymology- 5 How to Set Up a Bilayer System- 6 Fusion of Liposomes to Planar Bilayers- 7 Incorporation of Ion Channels by Fusion- II Nicotinic Acetylcholine Receptor- 8 The Reconstituted Acetylcholine Receptor- 9 Immunologic Analysis of the Acetylcholine Receptor- 10 Function of Acetylcholine Receptors in Reconstituted Liposomes- III Sodium Channel- 11 Skeletal Muscle Sodium Channels: Isolation and Reconstitution- 12 Reconstitution of the Sodium Channel from Electrophorus electricus- 13 The Reconstituted Sodium Channel from Brain- 14 Gating of Batrachotoxin-Activated Sodium Channels in Lipid Bilayers- 15 Ion Conduction Through Sodium Channels in Planar Lipid Bilayers- 16 Blocking Pharmacology of Batrachotoxin-Activated Sodium Channels- IV Other Channels in Model Membranes- 17 The Large Calcium-Activated Potassium Channel- 18 The Sarcoplasmic Reticulum Potassium Channel: Lipid Effects- 19 Characterization of Dihydropyridine-Sensitive Calcium Channels from Purified Skeletal Muscle Transverse Tubules- 20 Calcium Channels- 21 Phosphorylation of a Reconstituted Potassium Channel- 22 Voltage Gating in VDAC: Toward a Molecular Mechanism- 23 Analysis and Chemical Modification of Bacterial Porins

448 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the role of 1-carriets in the transfer of ions across thin lipid bilayer membranes is presented, focusing on simpler systems, i.e., the lipid-soluble ions, the 1-1 carriets, a simple pore and a substance which prodeces interacting pores.
Abstract: There are now well-established examples of carriers and pores which facilitate the transfer of ions across thin lipid membranes. In the absence of such agents, lipid bilayer membranes are extremely impermeable to the common inorganic ions. Thus, the conductance of a pure lecithin + decane or glyceryl mono-oleate + decane membrane in M/10 NaCl is less than10−9Ω −1 cm−2. However, on the addition of small lipid-soluble molecules such as valinomycin, or surface-active polypeptides such as gramicidin A, the conductance may become so high (> 10−1 ω−l cm−2) that the resistance of the membrane merges into that of the aqueous phase. This review is concerned with the extent to which we now understand how these added substances transfer ions across lipid membranes. Attention has been concentrated on the simpler systems, i.e. the lipid-soluble ions, the 1–1 carriets, a simple pore and, with some loss of simplicity, a substance which prodeces interacting pores. Only molecules of known primary structure are discussed.

385 citations

Journal ArticleDOI
TL;DR: Values of the selectivity constants and of δΔFl for the −CH2−and −OH groups in lecithin suggest that partitioned solutes are mainly located in a region slightly less hydrophobic than octanol and similar to C5H11OH in its solvent properties.
Abstract: Nonelectrolyte partition coefficients (K's) and free energies of solution (ΔF l 's) in dimyristoyl lecithin liposomes and in bulk nonpolar solvents were compared. Individual substituent groups tend to have consistent effects onK, permitting the extraction of incremental free energies (δΔF), enthalpies (δΔH), and entropies (δΔS) of partition and of solution. Values of the selectivity constants and of δΔF l for the −CH2−and −OH groups in lecithin suggest that partitioned solutes are mainly located in a region slightly less hydrophobic than octanol and similar to C5H11OH in its solvent properties. Lecithin discriminates against branched solutes more than does a bulk solvent with the sames value. Below the endothermic phase-transition temperature (i.e., when the hydrocarbon tails “freeze”), ΔS and ΔH of partition increase 10-fold,K jumps down slightly, ΔS and ΔH of solution reverse in sign from negative to positive, and the Barclay-Butler constants become more positive. Partition in lecithin and in erythrocytes is similar, except for the absence of surface charge effects in lecithin. Resistance to nonelectrolyte permeation is inhomogeneously distributed through the bilayer, and the region of maximum partition does not provide the rate-limiting barrier. An appendix derives a simple general expression for the nonelectrolyte permeability of a membrane that may be asymmetrical, may have position-dependent partition coefficients and diffusion coefficients, and may have significant interfacial resistances.

377 citations

References
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Book
01 Jan 1965

734 citations