Lipid membrane instability and poration driven by capacitive charging

A new model for the interaction of an electric pulse with a lipid membrane is proposed. Using this model we show that when a DC electric pulse is applied to an insulating lipid membrane separating fluids with different conductivities, the capacitive charging current through the membrane drives electrohydrodynamic flow that destabilizes the membrane. The instability is transient and decays as the membrane charges. The bulk conductivity mismatch plays an essential role in this instability because it results in a different rate of charge accumulation on the membrane's physical surfaces. Shearing stresses created by the electric field acting on its own induced free charge are non-zero as long as the charge imbalance exists. Accordingly, the most unstable mode is related to the ratio of membrane charging time and the electrohydrodynamic time.Comment: 4 pages, 4 figure

Fluid flow beneath a semipermeable membrane during drying processes

The dynamic interactions between a semipermeable membrane and a long, thin layer of liquid beneath it are investigated in the context of drying processes. The membrane separates two aqueous solutions of sugar, and the transport of water across the membrane is driven by concentration and pressure gradients across it. A model is formulated using a long-wave approximation that includes the effects of volume loss due to water transport across the membrane, the incompressibility and bending stiffness of the membrane, and the dynamical effects that arise owing to the viscous stresses generated by the fluid flow. This model is first applied to study the desiccation of a sessile vesicle that is clamped to a rigid substrate and then also to study the behavior of blisters on laminated substrates. For each problem, equilibrium membrane shapes are obtained and their bifurcation structures are described as the sugar concentration above the membrane is varied. It is demonstrated that a wrinkled membrane coarsens to lessen the frequency of wrinkles and that if the membrane is clamped symmetrically so that it meets the substrate at a nonzero angle, then the membrane favors an asymmetric shape as water is drawn out through it

Thin-film flow beneath a vesicle during adhesion processes

Lubrication theory is used to model the dynamics of a vesicle as it adheres to a rigid horizontal substrate. Travelling-wave solutions are obtained and used to estimate the spreading of the vesicle along the substrate. The results are compared with boundary-integral simulations, and good agreement is demonstrated in cases where the vesicle's shape is already close to its equilibrium shape. In the more general case, there is a transient motion that is not described by scalings obtained using lubrication theory

Mitochondria-rough-ER contacts in the liver regulate systemic lipid homeostasis

Contacts between organelles create microdomains that play major roles in regulating key intracellular activities and signaling pathways, but whether they also regulate systemic functions remains unknown. Here, we report the ultrastructural organization and dynamics of the inter-organellar contact established by sheets of curved rough endoplasmic reticulum closely wrapped around the mitochondria (wrappER). To elucidate the in vivo function of this contact, mouse liver fractions enriched in wrappER-associated mitochondria are analyzed by transcriptomics, proteomics, and lipidomics. The biochemical signature of the wrappER points to a role in the biogenesis of very-low-density lipoproteins (VLDL). Altering wrappER-mitochondria contacts curtails VLDL secretion and increases hepatic fatty acids, lipid droplets, and neutral lipid content. Conversely, acute liver-specific ablation of Mttp, the most upstream regulator of VLDL biogenesis, recapitulates this hepatic dyslipidemia phenotype and promotes remodeling of the wrappER-mitochondria contact. The discovery that liver wrappER-mitochondria contacts participate in VLDL biology suggests an involvement of inter-organelle contacts in systemic lipid homeostasis.Fil: Anastasia, Irene. Laval University; Canadá. Brain Research Center; CanadáFil: Ilacqua, Nicolò. Laval University; Canadá. Brain Research Center; CanadáFil: Raimondi, Andrea. San Raffaele Scientific Institute; ItaliaFil: Lemieux, Philippe. Brain Research Center; CanadáFil: Ghandehari-Alavijeh, Rana. Brain Research Center; CanadáFil: Faure, Guilhem. Broad Institute of MIT and Harvard; Estados Unidos. National Center For Biotechnology Information; Estados UnidosFil: Mekhedov, Sergei L.. National Center For Biotechnology Information ; Estados UnidosFil: Williams, Kevin J.. University of California at Los Angeles. School of Medicine; Estados UnidosFil: Caicci, Federico. Università di Padova; ItaliaFil: Valle, Giorgio. Università di Padova; ItaliaFil: Giacomello, Marta. Università di Padova; ItaliaFil: Quiroga, Ariel Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina. University of Alberta; CanadáFil: Lehner, Richard. University of Alberta; CanadáFil: Miksis, Michael J.. Northwestern University; Estados UnidosFil: Toth, Katalin. University of Ottawa; CanadáFil: de Aguiar Vallim, Thomas Q.. University of California at Los Angeles. School of Medicine; Estados UnidosFil: Koonin, Eugene V.. National Center For Biotechnology Information ; Estados UnidosFil: Scorrano, Luca. Università di Padova; ItaliaFil: Pellegrini, Luca. Laval University; Canad

Information theory analysis of Australian humpback whale song

Songs produced by migrating whales were recorded off the coast of Queensland, Australia, over six consecutive weeks in 2003. Forty-eight independent song sessions were analyzed using information theory techniques. The average length of the songs estimated by correlation analysis was approximately 100 units, with song sessions lasting from 300 to over 3100 units. Song entropy, a measure of structural constraints, was estimated using three different methodologies: (1) the independently identically distributed model, (2) a first-order Markov model, and (3) the nonparametric sliding window match length (SWML) method, as described by Suzuki et al. [(2006). “Information entropy of humpback whale song,” J. Acoust. Soc. Am. 119, 1849–1866]. The analysis finds that the song sequences of migrating Australian whales are consistent with the hierarchical structure proposed by Payne and McVay [(1971). “Songs of humpback whales,” Science 173, 587–597], and recently supported mathematically by Suzuki et al. (2006) for singers on the Hawaiian breeding grounds. Both the SWML entropy estimates and the song lengths for the Australian singers in 2003 were lower than that reported by Suzuki et al. (2006) for Hawaiian whales in 1976–1978; however, song redundancy did not differ between these two populations separated spatially and temporally. The average total information in the sequence of units in Australian song was approximately 35 bits/song. Aberrant songs (8%) yielded entropies similar to the typical songs

Complex interfacial flows. Final report for period August 1, 1997 - July 31, 2001

The objective of this grant was to study complex interfacial flows. Here we report on several problems considered. In particular we have investigated the motion of a liquid along a second liquid interface, we have investigated a canonical problem associated with the rupture of a viscous interface, we have investigated the dynamics of a gas bubble or drop in an inclined parallel walled channel under gravity with and without the presence of surfactants, we have studied the dynamics of a dry spot in a thin liquid film and we have developed a numerical code to study the dynamics of a liquid interface in a parallel walled channel. In addition, two students have completed their Ph.D. thesis during this grant period