626 research outputs found
Measuring Gaussian rigidity using curved substrates
The Gaussian (saddle splay) rigidity of fluid membranes controls their
equilibrium topology but is notoriously difficult to measure. In lipid
mixtures, typical of living cells, linear interfaces separate liquid ordered
(LO) from liquid disordered (LD) bilayer phases at subcritical temperatures.
Here we consider such membranes supported by curved supports that thereby
control the membrane curvatures. We show how spectral analysis of the
fluctuations of the LO-LD interface provides a novel way of measuring the
difference in Gaussian rigidity between the two phases. We provide a number of
conditions for such interface fluctuations to be both experimentally measurable
and sufficiently sensitive to the value of the Gaussian rigidity, whilst
remaining in the perturbative regime of our analysis.Comment: 5 pages, 3 figures. v2: version accepted for publicatio
Hydro-osmotic instabilities in active membrane tubes
We study a membrane tube with unidirectional ion pumps driving an osmotic pressure difference. A pressure driven peristaltic instability is identified, qualitatively distinct from similar tension-driven Rayleigh type instabilities on membrane tubes. We discuss how this instability could be related to the function and biogenesis of membrane bound organelles, in particular the contractile vacuole complex. The unusually long natural wavelength of this instability is in agreement with that observed in cells
Dynamics of passive and active membrane tubes
Utilising Onsager's variational formulation, we derive dynamical equations
for the relaxation of a fluid membrane tube in the limit of small deformation,
allowing for a contrast of solvent viscosity across the membrane and variations
in surface tension due to membrane incompressibility. We compute the relaxation
rates, recovering known results in the case of purely axis-symmetric
perturbations and making new predictions for higher order (azimuthal)
-modes. We analyse the long and short wavelength limits of these modes by
making use of various asymptotic arguments. We incorporate stochastic terms to
our dynamical equations suitable to describe both passive thermal forces and
non-equilibrium active forces. We derive expressions for the fluctuation
amplitudes, an effective temperature associated with active fluctuations, and
the power spectral density for both the thermal and active fluctuations. We
discuss an experimental assay that might enable measurement of these
fluctuations to infer the properties of the active noise. Finally we discuss
our results in the context of active membranes more generally and give an
overview of some open questions in the field.Comment: 14 pages, 9 figure
Increased cortical excitability after selective REM sleep deprivation in healthy humans: a transcranial magnetic stimulation study
REM sleep has antiepileptogenic properties whereas, its loss is known to have a proconvulsive role. However, the mechanisms underlying the proepileptogenic effects of REM sleep deprivation are yet not fully understood. The aim of our study was to evaluate the effects of selective REM sleep deprivation (SRD) on cortical excitability in healthy subjects by means of transcranial magnetic stimulation (TMS)
Use of anti-TNF Etanercept in paediatric patients with autoimmune disease and ocular involvement: the Parma experience
Familial vesicoureteral reflux: testing replication of linkage in seven new multigenerational kindreds
IgA nephropathy: the presence of familial disease does not confer an increased risk for progression
Renal outcome in patients with congenital anomalies of the kidney and urinary tract.
15openopenSanna-Cherchi S; Ravani P; Corbani V; Parodi S; Haupt R; Piaggio G; Innocenti ML; Somenzi D; Trivelli A; Caridi G; Izzi C; Scolari F; Mattioli G; Allegri L; Ghiggeri GM.Sanna Cherchi, S; Ravani, P; Corbani, V; Parodi, S; Haupt, R; Piaggio, G; Innocenti, Ml; Somenzi, D; Trivelli, A; Caridi, G; Izzi, C; Scolari, Francesco; Mattioli, G; Allegri, L; Ghiggeri, G. M
Familial aggregation of primary glomerulonephritis in an Italian population isolate: Valtrompia study
Hypothalamic arcuate nucleus glucokinase regulates insulin secretion and glucose homeostasis
Aims Glucokinase (GK) serves as a glucose sensor in several tissues including glucose‐sensitive neurons of the arcuate nucleus within the hypothalamus. We have previously demonstrated a role for arcuate GK in the regulation of food and glucose intake. However, its role in the regulation of glucose homeostasis is less clear. We therefore sought to investigate the role of arcuate GK in the regulation of glucose homeostasis. Materials and Methods Recombinant adeno‐associated virus expressing either GK or an antisense GK construct was used to alter GK activity specifically in the hypothalamic arcuate nucleus. GK activity in this nucleus was also increased by stereotactic injection of the GK activator, compound A. The effect of altered arcuate nucleus GK activity on glucose homeostasis was subsequently investigated using glucose and insulin tolerance tests. Results Increased GK activity specifically within the arcuate nucleus increased insulin secretion and improved glucose tolerance in rats during oral glucose tolerance tests. Decreased GK activity in this nucleus reduced insulin secretion and increased glucose levels during the same tests. Insulin sensitivity was not affected in either case. The effect of arcuate nucleus glucokinase was maintained in a model of type 2 diabetes. Conclusions These results demonstrate a role for arcuate nucleus GK in systemic glucose homeostasis
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