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Proceedings ArticleDOI

Effect of Na/K ratio on fluidization of lipid monolayers

05 Nov 2020-Vol. 2265, Iss: 1, pp 030039
TL;DR: In this article, the effect of the Na/K ratio on rigidity or compressibility of Dipalmitoyl Phosphatidylcholine (DPPC) membranes was studied.
Abstract: The Na/K ratio is well known to generate and control neural signals. We present here results on studies of the effect of Na/K ratio on rigidity or compressibility (κ) of Langmuir monolayers of Dipalmitoyl Phosphatidylcholine (DPPC), a major constituent of cell membranes. A considerable increase in κ (κNa) is seen with 10-2N Na+ ions in the aqueous subphase, while the increase with 10-2N K+ ions (κK) is marginal. For a Na/K = 1 mixture of the same overall ion concentration, κK>κ>κNa but it lies closer to κNa. For Na/K = 2/3, the increase in κ over the equimolar value is very small whereas for Na/K = 1/4 the κ value is very close to κK. These results indicate a new role of Na/K ratio, that of controlling the fluidity of the cell membrane.
References
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Journal ArticleDOI
TL;DR: It is demonstrated that the main effect of monovalent salt on a phospholipid membrane is determined by cations binding to the carbonyl region of a membrane, while chloride anions mostly stay in the water phase.
Abstract: To gain a better understanding of how monovalent salt under physiological conditions affects plasma membranes, we have performed 200 ns atomic-scale molecular dynamics simulations of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipid bilayers. These two systems provide representative models for the outer and inner leaflets of the plasma membrane, respectively. The implications of cation−lipid interactions in these lipid systems have been considered in two different aqueous salt solutions, namely NaCl and KCl, and the sensitivity of the results on the details of interactions used for ions is determined by repeating the simulations with two distinctly different force fields. We demonstrate that the main effect of monovalent salt on a phospholipid membrane is determined by cations binding to the carbonyl region of a membrane, while chloride anions mostly stay in the water phase. It turns out that the strength and character of the cation−lipid interactions are quite different for different types...

229 citations

Journal ArticleDOI
TL;DR: It is experimentally proved that the amount of ions present in the measuring system has a strong effect on the force needed to puncture a 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer with an atomic force microscope tip, highlighting the role that monovalent cations play upon membrane stability.

217 citations

Journal ArticleDOI
TL;DR: The extensive lipid-ion interaction networks and their transient formation between headgroups in a dipalmitoylphosphatidylcholine bilayer under physiological conditions are investigated and the spatial distribution of ion occupancy is imaged by frequency modulation atomic force microscopy.
Abstract: Various metal cations in physiological solutions interact with lipid headgroups in biological membranes, having an impact on their structure and stability, yet little is known about the molecular-scale dynamics of the lipid-ion interactions. Here we directly investigate the extensive lipid-ion interaction networks and their transient formation between headgroups in a dipalmitoylphosphatidylcholine bilayer under physiological conditions. The spatial distribution of ion occupancy is imaged in real space by frequency modulation atomic force microscopy with sub-\AA{}ngstrom resolution.

153 citations

Journal ArticleDOI
01 Sep 1996
TL;DR: In this paper, it was shown that the types and distributions of domain shapes formed throughout the coexistence region depend sensitively on the rate of monolayer compression, and that isotherms generated by compressing very slowly, or those generated at quick speeds but only after the film was left stagnant for a few hours, are markedly different from isotherm produced if the film were compressed within an hour after it was spread.
Abstract: Pressure–area isotherms of dipalmitoylphosphatidylcholine (DPPC) exhibit a two-phase region wherein domains of a liquid-condensed (LC) phase are dispersed in the less ordered liquid-expanded (LE) phase. Fluorescence microscopy has been used over the past years to visualize the shapes displayed by DPPC domains throughout the coexistence region; characteristic domain shapes include those resembling dimpled beans and S-like figures. In this paper we show that the types and distributions of domain shapes formed throughout the coexistence region depend sensitively on the rate of monolayer compression. Additionally, by comparing the relative proportion of LE and LC phases observed to that which is predicted by the isotherm, we find apparent violations of the lever rule. Most importantly, we find that if the monolayer is allowed to age in a state of two-phase coexistence for long times (approx. 12 h), the DPPC domains all become nearly circular. Finally, isotherms generated by compressing very slowly, or those generated at quick speeds but only after the film was left stagnant for a few hours, are markedly different from isotherms produced if the film was compressed within an hour after it was spread. One likely explanation for this behavior is the accumulation of air-borne impurities.

112 citations

Journal ArticleDOI
TL;DR: It was found that monovalent cations and Mg(2+) have similar phase behavior, causing DPPC monolayers to expand, while Ca(2+) induces condensation, and monolayer refractive index decreased with increasing cation concentration, which suggests that orientation of the alkyl chains change.

65 citations