48 research outputs found
Viscosity of fluid membranes measured from vesicle deformation
Viscosity is a key mechanical property of cell membranes that controls
time-dependent processes such as membrane deformation and diffusion of embedded
inclusions. Despite its importance, membrane viscosity remains poorly
characterized because existing methods rely on complex experimental designs
and/or analyses. Here, we describe a facile method to determine the viscosity
of bilayer membranes from the transient deformation of giant unilamellar
vesicles induced by a uniform electric field. The method is non-invasive, easy
to implement, probe-independent, high-throughput, and sensitive enough to
discern membrane viscosity of different lipid types, lipid phases, and polymers
in a wide range, from 10 to 10 Pa.s.m. It enables fast and
consistent collection of data that will advance understanding of biomembrane
dynamics
Fluctuation spectroscopy of giant unilamellar vesicles using confocal and phase contrast microscopy
A widely used method to measure the bending rigidity of bilayer membranes is
fluctuation spectroscopy, which analyses the thermally-driven membrane
undulations of giant unilamellar vesicles recorded with either phase-contrast
or confocal microscopy. Here, we analyze the fluctuations of the same vesicle
using both techniques and obtain consistent values for the bending modulus. We
discuss the factors that may lead to discrepancies
Assessing membrane material properties from the response of giant unilamellar vesicles to electric fields
Knowledge of the material properties of membranes is crucial to understanding cell viability and physiology. A number of methods have been developed to probe membranes in vitro, utilizing the response of minimal biomimetic membrane models to an external perturbation. In this review, we focus on techniques employing giant unilamellar vesicles (GUVs), model membrane systems, often referred to as minimal artificial cells because of the potential they offer to mimick certain cellular features. When exposed to electric fields, GUV deformation, dynamic response and poration can be used to deduce properties such as bending rigidity, pore edge tension, membrane capacitance, surface shear viscosity, excess area and membrane stability. We present a succinct overview of these techniques, which require only simple instrumentation, available in many labs, as well as reasonably facile experimental implementation and analysis.
Graphical abstrac
Development and results of the epilepsy surgery in Armenia: hope for a better future
PurposeWe present our experience with the national epilepsy surgery program in Armenia by tracing the development of epilepsy surgery in the largest pediatric neurology department at “Arabkir” Medical Center. This development was possible on the basis of a strong collaboration with the Epilepsy Surgery center at the University Hospital “Sofia St. Ivan Rilski,” Sofia, Bulgaria.Materials and methodsOur material included 28 consecutive patients with lesional drug-resistant epilepsy evaluated. All patients underwent 3 T MRI and Video-EEG monitoring. Brain 18FDG-PET was done in 13 patients in St. Petersburg. Fifteen patients (53%) had preoperative neuropsychological examination before surgery. All operations were done by the same neurosurgical team on site in Arabkir Hospital.ResultsThe majority of the patients in our cohort benefited from the epilepsy surgery as 25 (89%) are free of disabling seizures (Engel class I) and three patients (11%) did not improve substantially (Engel class IV). Eleven patients (39%) are already ASM-free after surgery, 4 (14%) are on monotherapy, 11(39%) get two drugs, and 2(7%) are on polytherapy, one of them still continues having seizures. In 12 patients (43%), we were able either to withdraw therapy or to decrease one of the ASM.ConclusionWe believe that, although small, yet encompassing patients along the usual age spectrum and with the most frequent pathologies of drug-resistant epilepsies, our experience can serve as a model to develop epilepsy surgery in countries with limited resources
Electrohydrodynamic model of vesicle deformation in alternating electric fields
We develop an analytical theory to explain the experimentally-observed
morphological transitions of giant vesicles induced by AC electric fields (1).
The model treats the inner and suspending media as lossy dielectrics, while the
membrane as an ion-impermeable flexible incompressible-fluid sheet. The vesicle
shape is obtained by balancing electric, hydrodynamic, and bending stresses
exerted on the membrane. Considering a nearly spherical vesicle, the solution
to the electrohydrodynamic problem is obtained as a regular perturbation
expansion in the excess area.
The theory predicts that stationary vesicle deformation depends on field
frequency and conductivity conditions. If the inner fluid is more conducting
than the suspending medium, the vesicle always adopts a prolate shape. In the
opposite case, the vesicle undergoes a transition from a prolate to oblate
ellipsoid at a critical frequency, which the theory identifies with the inverse
membrane charging time. At frequencies higher than the inverse Maxwell-Wagner
polarization time, the electrohydrodynamic stresses become too small to alter
the vesicle's quasi-spherical rest shape. The analysis shows that the evolution
towards the stationary vesicle deformation strongly depends on membrane
properties such as viscosity. The model can be applied to rationalize the
transient and steady deformation of biological cells in electric fields
De Novo Mutations in Synaptic Transmission Genes Including DNM1 Cause Epileptic Encephalopathies
Correction to The American Journal of Human Genetics, Volume 95, Issue 4, 2 October 2014, Pages 360-370. Volume 100, Issue 1, 5 January 2017, Page 179.Peer reviewe