Dipole Potentials Indicate Restructuring of the Membrane Interface Induced by Gadolinium and Beryllium Ions

Abstract

The dipole component of the membrane boundary potential, phi(d), is an integral parameter that may report on the conformational state of the lipid headgroups and their hydration. In this work, we describe an experimental approach to measurements of the dipole potential changes, Deltaphi(d), and apply it in studies of Be(2+) and Gd(3+) interactions with membranes composed of phosphatidylserine (PS), phosphatidylcholine (PC), and their mixtures. Deltaphi(d) is determined as the difference between the changes of the total boundary potential, phi(b), measured by the IFC method in planar lipid membranes and the surface potential, phi(s), determined from the electrophoretic mobility of liposomes. The Gouy-Chapman-Stern formalism, combined with the condition of mass balance, well describes the ion equilibria for these high-affinity cations. For the adsorption of Be(2+) and Gd(3+) to PC membranes, and of Mg(2+) to PS membranes, the values of Deltaphi(b) and Deltaphi(s) are the same, indicative of no change of phi(d). Binding of Gd(3+) to PS-containing membranes induces changes of phi(d) of opposite signs depending on the density of ionized PS headgroups in the bilayer. At low density, the induced Deltaphi(d) is negative (-30 mV), consistent with the effect of dehydration of the surface. At maximal density (pure PS, neutral pH), adsorption of Be(2+) or Gd(3+) induces an increase of phi(d) of 35 or 140 mV, respectively. The onset of the strong positive dipole effect on PS membranes with Gd(3+) is observed near the zero charge point and correlates with a six-fold increase of membrane tension. The observed phenomena may reflect concerted reorientation of dipole moments of PS headgroups as a result of ion adsorption and lipid condensation. Their possible implications to in-vivo effects of these high-affinity ions are discussed.

Thermal Transients Excite Neurons through Universal Intramembrane Mechanoelectrical Effects

“…This dual mechanism found by separately considering the temperature-dependent behavior in each membrane subregion explains the experimental shift of membrane current when multivalent ions (Mg 2þ and Gd 3þ ) that affect the surface charge [42] were added to one side of the membranes' solutions [16], while almost no effect was observed on membrane capacitance variations [slope in Figs. 3(e) and 3(g)]. Added together, the net thermal displacement current equals the product of the thermoelectric capacitance and the temperature's time derivative (see Sec.…”

“…In artificial membrane simulations under the experimental conditions of Shapiro et al [16] (symmetrical membranes −1∶1∶1 PE:PC:PS and 1∶1 PE∶PC, wherein the PS is a negatively charged phospholipid molecule, while the PE and PC are nearly uncharged [61]), surface charge change due to ions absorption were modeled through the Langmuir isotherm [42], TABLE II. POPC membranes' thermal dimensional change parameters used in the theoretical framework (see Refs.…”

“…where S is the maximal charge density of the ions' potential membrane binding sites-equals to 0.2 C=m 2 that corresponds to 0.6 nm 2 per lipid molecule for membranes in fluid phase condition [31,42]; f PS and f PE and PC are the molecular fraction of PS and PE/PC; z l , c l , and K l−PS are the valency, concentration close to the membrane, and absorption factor to PS of the multivalent Mg 2þ or Gd 3þ ions [16], respectively; K l−PE=PC is the multivalent ions' absorption factor to PE and PC [42,62]; and c h and K h are the concentration close to the membrane and absorption factor to PS of the Na þ ions [63] (see Table SI in Supplemental Material [40] for parameter values).…”

A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury

“…5). 52,53 We have shown previously that MSCs of different types exist in astrocytes, and different MSCs can be used by cells to deal with different stimuli. 40 In astrocytes, cation currents activated by pressure applied to a patch can be blocked by GsMTx4, a known inhibitor specific to cationic MSCs, 54 whereas Ca 2 + influx activated by swelling cannot be blocked.…”

How did cells get their size?

“…When multivalent ions, DNA, and charged peptides (e.g., bacterial S-layer proteins, poly-l-lysine) bind to bilayers, they can mechanically stabilize them via induced lipid ordering, rigidification, and decreased transversal compliance effects (Sackmann, 1994;Dan, 1996;Murray et al, 1999;Schuster et al, 1999;Norris et al, 1999;Ermakov et al, 2001). Say RPP was a polyionic peptide that bound to counterionic membrane lipids, enhancing liposome stability, and simultaneously (to make this a best-case scenario) increasing the rate of replicase self-copying and/or replicase-induced peptide formation.…”