Mechanical calorimetry of large dimyristoylphosphatidylcholine vesicles in the phase transition region

Evans, Evan; Kwok, R.

doi:10.1021/bi00263a007

Cited by 158 publications

(89 citation statements)

References 18 publications

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“…Membrane area compressibilities (19,26) and correspondingly the bending elasticity (27,28) increase greatly in the chainmelting regime. This phenomenon, established experimentally for unilamellar phosphatidylcholine vesicles, is likely to be general for all lipids, because it arises from the energetically facile interconversion of the coexisting lipid states that enhances the fluctuations in membrane area at the melting point.…”

Section: Discussion Why Do Structural Changes Occur Close To the Meltmentioning

confidence: 99%

See 1 more Smart Citation

Network formation of lipid membranes: Triggering structural transitions by chain melting

Schneider

Marsh

Jahn

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

120

130

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Phospholipids when dispersed in excess water generally form vesicular membrane structures. Cryo-transmission and freeze-fracture electron microscopy are combined here with calorimetry and viscometry to demonstrate the reversible conversion of phosphatidylglycerol aqueous vesicle suspensions to a three-dimensional structure that consists of extended bilayer networks. Thermodynamic analysis indicates that the structural transitions arise from two effects: (i) the enhanced membrane elasticity accompanying the lipid state fluctuations on chain melting and (ii) solventassociated interactions (including electrostatics) that favor a change in membrane curvature. The material properties of the hydrogels and their reversible formation offer the possibility of future applications, for example in drug delivery, the design of structural switches, or for understanding vesicle fusion or fission processes. Lipids may undergo a cooperative melting reaction linked to the loss in conformational order of the lipid chains (1). This transition is accompanied by a large change of the internal energy (or enthalpy) that can be studied by calorimetry. It has long been known that the melting profiles are influenced by secondary components, e.g., proteins (2), cholesterol, or anesthetics (3, 4). Phase diagrams of lipid mixtures usually are constructed as a function of the chemical potential of the components and the temperature (5). Another kind of possible transition involves changes in vesicular shape. These transitions have been studied in some detail by theoretical means, resulting in phase diagrams for vesicle structure as a function of the elastic constants (6, 7). Changes in these constants can explain theoretically the wealth of shapes of erythrocytes (8). There are therefore two kinds of phase diagrams found for lipid systems: one describing the calorimetric features of chain melting, mainly dependent on short-range cooperative events within the membrane plane, and the other describing transitions in shape and long-range order influenced by changes in the elastic constants.Although seemingly different features of a lipid system, the elastic constants and the heat capacity of the lipid membrane are related because they are coupled to thermodynamic fluctuations in the membrane properties (9). Maximum elasticity is achieved in the regime of ordered (gel)-fluid phase coexistence (10), which implies that close to the heat capacity maximum the elastic constants change markedly and as a consequence the membranes become more flexible. From this it is expected that changes in structural equilibria may be found close to the chain-melting transition.We demonstrate here thermodynamically how the structural changes couple to the chain melting. Large viscosity changes of dimyristoyl phosphatidylglycerol (DMPG) dispersions close to the calorimetric melting transition have been reported that are accompanied by marked changes in heat capacity, light scattering, and electrical conductance (11,12). The changes in viscosity suggest a change in the l...

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Section: Discussion Why Do Structural Changes Occur Close To the Meltmentioning

confidence: 99%

“…2C). The different vesicular geometry is a consequence of the different bending elasticities for the ordered (gel) and the fluid phases (18,19). The lipid phase in the melting regime is not vesicular and no localized bounded structures can be seen (Fig.…”

mentioning

confidence: 99%

Network formation of lipid membranes: Triggering structural transitions by chain melting

Schneider

Marsh

Jahn

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

120

130

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“…In the micropipette technique, which was originally introduced by Evans and Kwok [34,35] and used for studying the mechanical properties of vesicles with great success [36], a micropipette of a few microns inner diameter is used to aspire individual objects. Using hydrostatic pressure, small pressure differences can be applied across the membrane and the induced deformation can be monitored using optical microscopy.…”

Section: Methods Relying On Micromanipulation Of Individual Capsulesmentioning

confidence: 99%

Mechanics of artificial microcapsules

2004

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“…It has been argued elsewhere (e.g., Bates & Wolfe, 1980;Evans & Kwok, 1982) that the most important factor determining the area elastic modulus is the possible existence of local regions of solid phase lipids in the membrane. In the liquid phase, this modulus is not expected to depend strongly on the lipid composition, though its dependence on protein concentration is harder to predict.…”

Section: Area Elastic Modulusmentioning

confidence: 98%

Dynamics of membrane exchange of the plasma membrane and the lysis of isolated protoplasts during rapid expansions in area

1985

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Summary.The plasma membrane of protoplasts isolated from rye leaves (Secale cereale L. cv. Puma) can withstand a maximum elastic stretching of about 2%. Larger area expansions involve the incorporation of new material into the membrane. The dynamics of this process during expansion from isotonic solutions and the probable frequency of lysis have been measured as a function of membrane tension in populations of protoplasts isolated from both co/d-acclimated and nonacclimated plants. To a first approximation, both increase exponentially with tension. An analytical solution is reported for the membrane tension as a function of time during an arbitrary expansion in area.

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Mechanical calorimetry of large dimyristoylphosphatidylcholine vesicles in the phase transition region

Cited by 158 publications

References 18 publications

Network formation of lipid membranes: Triggering structural transitions by chain melting

Network formation of lipid membranes: Triggering structural transitions by chain melting

Mechanics of artificial microcapsules

Dynamics of membrane exchange of the plasma membrane and the lysis of isolated protoplasts during rapid expansions in area

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