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

Is autonomic nervous system involved in restless legs syndrome during wakefulness?

OBJECTIVE: To investigate cardiovascular autonomic function in patients with restless leg syndrome (RLS) by means of cardiovascular reflexes and heart rate variability (HRV) during wakefulness.METHODS: Twelve RLS patients and 14 controls underwent cardiovascular function tests including head-up tilt test (HUTT), Valsalva maneuver, deep breathing, hand grip, and cold face. HRV analysis was performed in the frequency domain using both autoregressive (AR) and fast Fourier transform algorithms in rest supine condition and during HUTT.RESULTS: There was a significant increase in systolic blood pressure values in supine rest condition and a trend toward a lower Valsalva ratio in RLS patients with respect to controls. The significant and physiological changes of HRV at HUTT detected in healthy subjects were not found in RLS patients. CONCLUSION: RLS patients exhibit a tendency toward hypertension, reduced amplitude of both sympathetic and parasympathetic responses at HUTT, as well as blunted parasympathetic drive to blood pressure changes. These findings, if confirmed by more controlled studies, might support the hypothesis of auonomic nervous system involvement during wakefulness and consequently an enhanced cardiovascular risk in RLS

Renal apolipoprotein A-I amyloidosis: a rare and usually ignored cause of hereditary tubulointerstitial nephritis

12openopenGregorini G; Izzi C; Obici L; Tardanico R; Röcken C; Viola BF; Capistrano M; Donadei S; Biasi L; Scalvini T; Merlini G; Scolari F.Gregorini, G; Izzi, C; Obici, L; Tardanico, R; Röcken, C; Viola, Bf; Capistrano, M; Donadei, S; Biasi, L; Scalvini, T; Merlini, G; Scolari, Francesc

Urinary secretion and extracellular aggregation of mutant uromodulin isoforms

Uromodulin is exclusively expressed in the thick ascending limb and is the most abundant protein secreted in urine where it is found in high-molecular-weight polymers. Its biological functions are still elusive, but it is thought to play a protective role against urinary tract infection, calcium oxalate crystal formation, and regulation of water and salt balance in the thick ascending limb. Mutations in uromodulin are responsible for autosomal-dominant kidney diseases characterized by defective urine concentrating ability, hyperuricemia, gout, tubulointerstitial fibrosis, renal cysts, and chronic kidney disease. Previous in vitro studies found retention in the endoplasmic reticulum as a common feature of all uromodulin mutant isoforms. Both in vitro and in vivo we found that mutant isoforms partially escaped retention in the endoplasmic reticulum and reached the plasma membrane where they formed large extracellular aggregates that have a dominant-negative effect on coexpressed wild-type protein. Notably, mutant uromodulin excretion was detected in patients carrying uromodulin mutations. Thus, our results suggest that mutant uromodulin exerts a gain-of-function effect that can be exerted by both intra- and extracellular forms of the protein

Symptomatic nonconvulsive status epilepticus erroneously suggestive of sporadic Creutzfeldt-Jakob disease

Nonconvulsive status epilepticus (NCSE) may have heterogeneous presentations and differential diagnosis may be particularly difficult because clinical signs coupled with periodic EEG pattern are most often subtle or non-specific. Moreover, few cases of NCSE have been previously described as the presenting symptom of sporadic Creutzfeldt–Jakob disease (sCJD) [1,4,5,7]. We describe a patient with a NCSE strongly, but erroneously, suggestive of a probable sCJD