Vesicle fluctuations

Henrrksen J, Rowat AC, Ipscm JH (2004) Vesicle fluctuation analysis of the effects of sterols on membrane bending rigidity. Eur Biophys J 33(8) 732-741... 

Figure 10.7 Prolate vesicle fluctuations at r = 0.937 and Aao = 1.21. The elapsed time between snapshots is 6.3 s [22].

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

These chain models are well suited to investigate the dependence of tire phase behaviour on the molecular architecture and to explore the local properties (e.g., enriclnnent of amphiphiles at interfaces, molecular confonnations at interfaces). In order to investigate the effect of fluctuations on large length scales or the shapes of vesicles, more coarse-grained descriptions have to be explored. 

X. Michalet, D. Bensimon, B. Fourcade. Fluctuating vesicles of nonspherical topology. Phys Rev Lett 72 168-171, 1994. 

Other possible direct probes are optical experiments similar to studies [113] of vesicles but expanded towards shorter A (20-30 A). Alternatively neutron spin-echo studies of stacked bilayer arrays, which can probe the 10-30 A range [114], might possibly be applicable here. Finally, the x-ray grazing-incidence technique has been shown to be a powerful tool for studying short wavelength fluctuations at fluid interfaces [100]. The application of this technique to the investigation of membrane surface fluctuations can reasonably be expected in the near future [115,116]. 

H. Noguchi and G. Gompper, Dynamics of fluid vesicles in shear flow effect of membrane viscosity and thermal fluctuations, Phys. Rev. E 72, 011901 (2005). 

There are two distinct pools of HA in the brain (1) the neuronal pool and (2) the non-neuronal pool, mainly contributed by the mast cells. The turnover of HA in mast cells is slower than in neurons it is believed that the HA contribution from the mast cells is limited and that almost all brain histaminergic actions are the result of HA released by neurons (Haas Panula, 2003). The blood-brain barrier is impermeable to HA. HA in the brain is formed from L-histidine, an essential amino acid. HA synthesis occurs in two steps (1) neuronal uptake of L-histidine by L-amino acid transporters and (2) subsequent decarboxylation of l-histidine by a specific enzyme, L-histidine decarboxylase (E.C. 4.1.1.22). It appears that the availability of L-histidine is the rate-limiting step for the synthesis of HA. The enzyme HDC is selective for L-histidine and its activity displays circadian fluctuations (Orr Quay, 1975). HA synthesis can be reduced by inhibition of the enzyme HDC. a-Fluoromethylhistidine (a-FMH) is an irreversible and a highly selective inhibitor of HDC a single systemic injection of a-FMH (10-50 mg/kg) can produce up to 90% inhibition of HDC activity within 60-120 min (Monti, 1993). Once synthesized, HA is taken up into vesicles by the vesicular monoamine transporter and is stored until released. 

The favourable properties which mark out vesicles as protocell models were confirmed by computer simulation (Pohorill and Wilson, 1995). These researchers studied the molecular dynamics of simple membrane/water boundary layers the bilayer surface fluctuated in time and space. The model membrane consisted of glycerine-1-monooleate defects were present which allowed ion transport to occur, whereby negative ions passed through the bilayer more easily than positive ions. The membrane-water boundary layer should be particularly suited to reactions which are accelerated by heterogeneous catalysis. Thus, the authors believe that these vesicles fulfil almost all the conditions required for the first protocells on earth ... 

Veatch, S.L., Cicuta, P., Sengupta, P., Honerkamp-Smith, A., Holowka, D., Baird, B. Critical fluctuations in plasma membrane vesicles. ACS Chem. Biol. 2008, 3, 287-93. 

Flow does the release of neurotransmitter occur That the release is "quantal," i.e., involving the entire content of a vesicle, was established from the observation of miniature end-plate potentials. These are fluctuations in the postsynaptic potential observed under conditions of weak stimulation of the presynap-tic neuron. They reflect the randon release of neurotransmitter from individual vesicles.553 Normally, a strong impulse will release on the order of 100-200... 

Bivas, Isak, Free Energy of a Fluctuating Vesicle. Influence of the Fluctuations on the Laplace Law, 6, 93 see also Mechanical Properties of Lipid Bilayers Containing Grafted Lipids, 6, 207. 

Dobereiner, Hans-Gtinther, Fluctuating Vesicle Shapes, 6, 149 see also Xu, Liyu, 6, 181 Petrov, Peter G.,... 

Manneville, Jan-Baptiste, Magnification of Shape Fluctuations of Active Giant Unilamellar Vesicles, 6, 351. 

The kinetics of concentration quenching in vesicles can be described quantitatively in terms of the stochastic approach. This approach takes into account, first, the small (1-100) number of photosensitizer molecules in one vesicle and, second, the statistical character of their distribution in the vesicles. The small number of the photosensitizer molecules in a vesicle leads to a significant influence of the fluctuations of this number on the quenching kinetics. As shown in Phe-containing vesicles [134], under these conditions the stochastic approach describes the... 

Using cholesterol as the basis, a theoretical model to explain the observed changes in lipid domain interfacial area has been derived. The model shows that enhancement of lateral density fluctuation and lipid domain interfacial area caused by cholesterol is stronger at temperatures further from the transition temperature [132]. A decrease in the phase transition temperature of DPPC vesicles upon addition of antidepressants and phase separation at increased concentrations has also been reported [133],... 

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