Permeation characteristics of gramicidin conformers

To investigate the molecular origin of decreased conductance in variant gramicidin channels, we examined the current-voltage (IV) characteristics of single Val1-gramicidin A channels. Unlike standard channels, all variant channels showed pronounced rectification even though bathing solutions were symmetrical. Moreover, channels of lower conductance consistently showed more pronounced rectification. Analysis within the framework of a three-barrier, two-site, single-filing model indicates that the shape of the variant channel IVs could be best explained by an increase in binding affinity near one of the two channel entrances. This conclusion was further tested by characterizing single channel IVs in bi-ionic solutions having different cationic species at each channel entrance. In Cs/Na bi-ionic solutions, reversal potentials of variant channels often differed by a small but significant amount from those of standard channels. When a membrane potential was applied, the ionic currents tended to be reduced more when flowing from the Na+ side than the Cs+ side. These observations support the conclusion that variant channels have increased binding affinity at one end of the channel. Furthermore, H+ currents were increased while Ag+ currents were unaltered for most variant channels exhibiting decreased Na+ or Cs+ currents. The increased H+ conductance argues against long-range coulombic forces as the basis for decreased Na+ or Cs+ conductance while the normal Ag+ conductance suggests that the binding site field strength increases by a change in carbonyl geometry at the channel entrance

Simple catalytic cell for restoring He leak detector sensitivity on vacuum systems with high D{sub 2} backgrounds

The DIII-D National Fusion Facility at General Atomics focuses on plasma physics and fusion energy science. The DIII-D tokamak is a 35 m{sup 3} toroidal vacuum vessel with over 200 ports for diagnostic instrumentation, cryogenics, microwave heating, and four large neutral beam injectors. Maintaining vacuum in the 10{sup {minus}8} Torr range is crucial for producing high performance plasma discharges. He leak checking the DIII-D tokamak and the neutral beamlines has historically been difficult. D{sub 2} is used as the fuel gas in most plasma discharges and neutral beams. After plasma operations, D{sub 2} out-gassing from the torus walls and internal beamline components can exceed 10{sup {minus}4} std cc/s. The mass of the D{sub 2} molecule (4.028 u) is indistinguishable from that of the He atom (4.003 u) to a standard mass spectrometer leak detector. High levels of D{sub 2} reduce leak detector sensitivity and effectively mask the He trace gas signal rendering normal leak checking techniques ineffective. A simple apparatus was developed at GA to address these problems. It consists of a palladium based catalyst cell and associated valves and piping placed in series with the leak detector. This reduces the D{sub 2} throughput by a factor greater than 10,000, restoring leak detector sensitivity. This paper will briefly discuss the development of the cell, the physical processes involved, the tests performed to quantify and optimize the processes, and the operational results at DIII-D

Fluorescence anisotropy of diphenylhexatriene and its cationic Trimethylamino derivative in liquid dipalmitoylphosphatidylcholine liposomes: opposing responses to isoflurane

<p>Abstract</p> <p>Background</p> <p>The mechanism of action of volatile general anesthetics has not yet been resolved. In order to identify the effects of isoflurane on the membrane, we measured the steady-state anisotropy of two fluorescent probes that reside at different depths. Incorporation of anesthetic was confirmed by shifting of the main phase transition temperature.</p> <p>Results</p> <p>In liquid crystalline dipalmitoylphosphatidylcholine liposomes, isoflurane (7-25 mM in the bath) increases trimethylammonium-diphenylhexatriene fluorescence anisotropy by ~0.02 units and decreases diphenylhexatriene anisotropy by the same amount.</p> <p>Conclusions</p> <p>The anisotropy data suggest that isoflurane decreases non-axial dye mobility in the headgroup region, while increasing it in the tail region. We propose that these results reflect changes in the lateral pressure profile of the membrane.</p

Dissolved Oxygen Reduction in the DIII-D Neutral Beam Ion Source Cooling System

OAK-B135 Neutral beam ion sources (NBIS) are critical components for the neutral beam injection system supporting the DIII-D tokamak. The NBIS must be cooled with 3028 {ell}/m (800 gpm) of de-ionized and de-oxygenated water to protect the sources from overheating and failure. These ions sources are currently irreplaceable. Since the water cooled molybdenum components will oxidize in water almost instantaneously in the presence of dissolved oxygen (DO), de-oxygenation is extremely important in the NBIS water system. Under normal beam operation the DO level is kept below 5 ppb. However, during weeknights and weekends when neutral beam is not in operation, the average DO level is maintained below 10 ppb by periodic circulation with a 74.6 kW (100 hp) pump, which consumes significant power. Experimental data indicated evidence of continuous oxygen diffusion through non-metallic hoses in the proximity of the NBIS. Because of the intermittent flow of the cooling water, the DO concentration at the ion source(s) could be even higher than measured downstream, and hence the concern of significant localized oxidation/corrosion. A new 3.73 kW (5 hp) auxiliary system, installed in the summer of 2003, is designed to significantly reduce the peak and the time-average DO levels in the water system and to consume only a fraction of the power

Model Channel Ion Currents in NaCl - SPC/E Solution with Applied-Field Molecular Dynamics

Using periodic boundary conditions and a constant applied field, we have simulated current flow through an 8.125 Angstrom internal diameter, rigid, atomistic channel with polar walls in a rigid membrane using explicit ions and SPC/E water. Channel and bath currents were computed from ten 10-ns trajectories for each of 10 different conditions of concentration and applied voltage. An electric field was applied uniformly throughout the system to all mobile atoms. On average, the resultant net electric field falls primarily across the membrane channel, as expected for two conductive baths separated by a membrane capacitance. The channel is rarely occupied by more than one ion. Current-voltage relations are concentration-dependent and superlinear at high concentrations.Comment: Accepted for publication in Biophysical Journa

Copper Complexes as Influenza Antivirals: Reduced Zebrafish Toxicity

Copper complexes have previously been developed to target His37 in influenza M2 and are effective blockers of both the wild type (WT) and the amantadine-resistant M2S31N. Here, we report that the complexes were much less toxic to zebrafish than CuCl2. In addition, we characterized albumin binding, mutagenicity, and virus resistance formation of these metal complexes, and employed steered molecular dynamics simulations to explore whether the complexes would fit in M2. We also examined their anti-viral efficacy in a multi-generation cell culture assay to extend the previous work with an initial-infection assay, discovering that this is complicated by cell culture medium components. The number of copper ions binding to bovine serum albumin (BSA) correlates well with the number of surface histidines and BSA binding affinity is low compared to M2. No mutagenicity of the complexes was observed when compared to sodium azide. After 10 passages of virus in MDCK culture, the EC50 was unchanged for each of the complexes, i.e. resistance did not develop. The simulations revealed that the compounds fit well in the M2 channel, much like amantadine

Water alignment, dipolar interactions, and multiple proton occupancy during water-wire proton transport

A discrete multistate kinetic model for water-wire proton transport is constructed and analyzed using Monte-Carlo simulations. The model allows for each water molecule to be in one of three states: oxygen lone pairs pointing leftward, pointing rightward, or protonated (H$_{3}$O$^{+}$). Specific rules for transitions among these states are defined as protons hop across successive water oxygens. We then extend the model to include water-channel interactions that preferentially align the water dipoles, nearest-neighbor dipolar coupling interactions, and coulombic repulsion. Extensive Monte-Carlo simulations were performed and the observed qualitative physical behaviors discussed. We find the parameters that allow the model to exhibit superlinear and sublinear current-voltage relationships and show why alignment fields, whether generated by interactions with the pore interior or by membrane potentials {\it always} decrease the proton current. The simulations also reveal a ``lubrication'' mechanism that suppresses water dipole interactions when the channel is multiply occupied by protons. This effect can account for an observed sublinear-to-superlinear transition in the current-voltage relationship

The orthogonal-oblique bi-level model of the Outcome Questionnaire (OQ-45.2) : the case of the Polish factorial normalization

Aim. The aim of this project was to conduct the cross-cultural factorial validation of the Outcome Questionnaire (OQ-45.2) using the Polish population. Material and method. Data were obtained from day-patients (n = 211), inpatients (n = 234), outpatients (n = 137) and non-patients (n = 426). Statistical analyses included: parallel analysis, exploratory factor analysis, confirmatory factor analysis, correlation analysis, criterion equivalence, clinical significance and reliable change index, and test-retest. Results. Statistical analyses provided the strongest support for the bi-level model of the total score, five orthogonal (subscales specific for the Polish OQ, i.e. Social Conflicts and Addictive Behaviors; and original yet modified subscales, i.e. Symptom Distress, Interpersonal Relations, and Social Role), and two oblique factors (Somatization and Anxiety, Social Role 2). The psychometric properties of the Polish OQ were found to be adequate and similar to the original American OQ and its international adaptations. Specific for the Polish OQ cutoff scores for clinical significance were established. The role of cultural differences and the passage of time in the process of the cross-cultural validation were elaborated upon. Conclusions. The Polish version of the OQ 45-2 has been recognized as an instrument adequately measuring general functioning as well as specific areas of functioning of the individual (i.e. interpersonal relations; social role performance; social conflicts; symptom distress; somatization and anxiety; addictive behaviors). Results of this factorial analysis seem to be valuable for both clinicians using the OQ-45.2 and for creators of any psychotherapy outcome measure