Effect of Temperature on the Structure of Charged Membranes

Abstract

Interactions between charged and neutral self-assembled phospholipid membranes are well understood and take into account temperature dependence. Yet, the manner in which the structure of the membrane is affected by temperature was hardly studied. Here we study the effect of temperature on the thickness, area per lipid, and volume per lipid of charged membranes. Two types of membranes were studied: membranes composed of charged lipids and dipolar (neutral) membranes that adsorbed divalent cations and became charged. Small-angle X-ray scattering data demonstrate that the thickness of charged membranes decreases with temperature. Wide-angle X-ray scattering data show that the area per headgroup increases with temperature. Intrinsically charged membranes linearly thin with temperature, whereas neutral membranes that adsorb divalent ions and become charged show an exponential decrease of their thickness. The data indicate that, on average, the tails shorten as the temperature rises. We attribute this behavior to higher lipid tail entropy and to the weaker electrostatic screening of the charged headgroups, by their counterions, at elevated temperatures. The latter effect leads to stronger electrostatic repulsion between the charged headgroups that increases the area per headgroup and decreases the bilayer thickness.

The temperature-dependent physical state of polar lipids and their miscibility impact the topography and mechanical properties of bilayer models of the milk fat globule membrane

“…Defects were also visible on the bilayers, like deposited objects resembling stacks of membranes (Figures 6A). The reduction in H measured at 6°C ( Figure 2C) could be explained by the thickening of the l d -phase phospholipids upon cooling, as previously reported for zwitterionic PCs [33,57]. More phospholipids than high-Tm ones may undergo phase transition as the temperature decreases below room temperature (Figure 2A), Noteworthy, the F B values obtained at 6°C followed the general trend of the increase recorded at 35°C and 25°C ( Figure 5) whereas images showed a drastic change in the microscopic organization of the bilayer ( Figure 6A).…”

Thermal Transients Excite Neurons through Universal Intramembrane Mechanoelectrical Effects

“…3(a) and 3(b)]. These dimensional changes have been observed in a range of different model membranes, including POPC, SOPC, DPhyPC, and more [30][31][32][33], and are putatively attributed to entropically driven shortening of the phospholipids' tails [ Fig. 1(b)], a process termed trans-gauche isomerization [31,33].…”

“…We next examined how these changes compare to the membrane's capacitance thermal rate of change expected purely from temperature-induced dimensional changes, which were recently experimentally estimated using x-ray and neutron small-angle scattering measurements [30][31][32] and computationally reproduced using molecular dynamics simulations [33]. Using a naive plate capacitor assumption where C ¼ ½ðε m AÞ=δ , the 0.11 AE 0.03%=°C reduction in the phospholipid membrane thickness and 0.22 AE 0.03%=°C increase in the area per phospholipid molecule [see Fig.…”

“…(b) Schematized membrane thinning and area expansion under temperature elevation. This observed process [30][31][32][33] is thought to result from an increase in the phospholipid molecules' fatty acid chains trans-gauche rotational isomerization, which shortens the tails' effective length and increases the area per phospholipid molecule. Biophysically, these two phenomena contribute to a predictable increase in both the membrane hydrophobic core's and total capacitance.…”

“…To address this major apparent gap in the theoretical basis for thermal excitation, we deconstruct and analyze here alternative revised biophysical models (tentative and detailed), where the membrane's physical dimensions themselves also vary in response to the temperature changes, to accurately reflect direct experimental findings [30][31][32][33]. The new mechanoelectrical thermal activation (META) models calculate the effect of temperature change on the membrane electrical parameters directly and explicitly (rather than implicitly), and are found to both qualitatively and quantitatively predict empirical findings on thermal membrane capacitance increases [16,19,20,24], unraveling the two underlying sources for thermal membrane currents, and making it possible to indirectly estimate from neural stimulation results a significant new quantity, the membrane surface charge difference.…”