An Intermediate State of the {gamma}-Aminobutyric Acid Transporter GAT1 Revealed by Simultaneous Voltage Clamp and Fluorescence

The rat {gamma}-aminobutyric acid transporter GAT1 expressed in Xenopus oocytes was labeled at Cys74, and at one or more other sites, by tetramethylrhodamine-5-maleimide, without significantly altering GAT1 function. Voltage-jump relaxation analysis showed that fluorescence increased slightly and monotonically with hyperpolarization; the fluorescence at -140 mV was ~0.8% greater than at +60 mV. The time course of the fluorescence relaxations was mostly described by a single exponential with voltage-dependent but history-independent time constants ranging from ~20 ms at +60 mV to ~150 ms at -140 mV. The fluorescence did not saturate at the most negative potentials tested, and the midpoint of the fluorescence–voltage relation was at least 50 mV more negative than the midpoint of the charge–voltage relation previously identified with Na+ binding to GAT1. The presence of {gamma}-aminobutyric acid did not noticeably affect the fluorescence waveforms. The fluorescence signal depended on Na+ concentration with a Hill coefficient approaching 2. Increasing Cl- concentration modestly increased and accelerated the fluorescence relaxations for hyperpolarizing jumps. The fluorescence change was blocked by the GAT1 inhibitor, NO-711. For the W68L mutant of GAT1, the fluorescence relaxations occurred only during jumps to high positive potentials, in agreement with previous suggestions that this mutant is trapped in one conformational state except at these potentials. These observations suggest that the fluorescence signals monitor a novel state of GAT1, intermediate between the E*out and Eout states of Hilgemann, D.W., and C.-C. Lu (1999. J. Gen. Physiol. 114:459–476). Therefore, the study provides verification that conformational changes occur during GAT1 function

Non-Equilibrium Dynamics Contribute to Ion Selectivity in the KcsA Channel

The ability of biological ion channels to conduct selected ions across cell membranes is critical for the survival of both animal and bacterial cells. Numerous investigations of ion selectivity have been conducted over more than 50 years, yet the mechanisms whereby the channels select certain ions and reject others are not well understood. Here we report a new application of Jarzynski’s Equality to investigate the mechanism of ion selectivity using non-equilibrium molecular dynamics simulations of Na+ and K+ ions moving through the KcsA channel. The simulations show that the selectivity filter of KcsA adapts and responds to the presence of the ions with structural rearrangements that are different for Na+ and K+. These structural rearrangements facilitate entry of K+ ions into the selectivity filter and permeation through the channel, and rejection of Na+ ions. A mechanistic model of ion selectivity by this channel based on the results of the simulations relates the structural rearrangement of the selectivity filter to the differential dehydration of ions and multiple-ion occupancy and describes a mechanism to efficiently select and conduct K+. Estimates of the K+/Na+ selectivity ratio and steady state ion conductance for KcsA from the simulations are in good quantitative agreement with experimental measurements. This model also accurately describes experimental observations of channel block by cytoplasmic Na+ ions, the “punch through” relief of channel block by cytoplasmic positive voltages, and is consistent with the knock-on mechanism of ion permeation

Building a sustainable and desirable economy-in-society-in-nature

This report is a synthesis of ideas about what this new economy-in-society-innature could look like and how we might get there. Most of the ideas presented here are not new. The coauthors of this report have published them in various forms over the last several decades, and many others have expressed similar ideas in venues too numerous to mention. What is new is the timing and the situation. The time has come when we must make a transition. We have no choice. Our present path is clearly unsustainable. As Paul Raskin has said, Contrary to the conventional wisdom, it is business as usual that is the utopian fantasy; forging a new vision is the pragmatic necessity [10]. But we do have a choice about how to make the transition and what the new state of the world will be. We can engage in a global dialogue to envision the future we want, the theme of Rio+20, and then devise an adaptive strategy to get us there, or we can allow the current system to collapse and rebuild from a much worse starting point. We obviously argue for the former strategy. In this report, we discuss the need to focus more directly on the goal of sustainable human well-being rather than merely GDP growth. This includes protecting and restoring nature, achieving social and intergenerational fairness (including poverty alleviation), stabilizing population, and recognizing the significant nonmarket contributions to human well-being from natural and social capital. To do this, we need to develop better measures of progress that go well beyond GDP and begin to measure human well-being and its sustainability more directly

Cretaceous-to-recent record of elevated ³He/⁴He along the Hawaiian-Emperor volcanic chain

Helium isotopes are a robust geochemical tracer of a primordial mantle component in hot spot volcanism. The high ³He/⁴He (up to 35 RA, where RA is the atmospheric ³He/⁴He ratio of 1.39 X 10¯⁶) of some Hawaiian Island volcanism is perhaps the classic example. New results for picrites and basalts from the Hawaiian-Emperor seamount chain indicate that the hot spot has produced high ³He/⁴He lavas for at least the last 76 million years. Picrites erupted at 76 Ma have ³He/⁴He (10-14 RA), which is at the lower end of the range for the Hawaiian Islands but still above the range of modern mid-ocean ridge basalt (MORB; 6-10 RA). This was at a time when hot spot volcanism was occurring on thin lithosphere close to a spreading ridge and producing lava compositions otherwise nearly indistinguishable from MORB. After the hot spot and spreading center diverged during the Late Cretaceous, the hot spot produced lavas with significantly higher ³He/⁴He (up to 24 RA). Although ³He/⁴He ratios stabilized at relatively high values by 65 Ma, other chemical characteristics such as La/Yb and ⁸⁷Sr/⁸⁶Sr did not reach and stabilize at Hawaiian-Island-like values until ~45 Ma. Our limited ³He/⁴He record for the Hawaiian hot spot shows a poor correlation with plume flux estimates (calculated from bathymetry and residual gravity anomalies [Van Ark and Lin, 2004]). If ³He is a proxy for the quantity of primordial mantle material within the plume, then the lack of correlation between ³He/⁴He and calculated plume flux suggests that variation in primordial mantle flux is not the primary factor controlling total plume flux.Keywords: helium, Hawaiian-Emperor chain, MOR

Cosmological Distance Measurement of 12 Nearby Supernovae IIP with ROTSE-IIIB

We present cosmological analysis of 12 nearby ($z<0.06$) Type IIP supernovae (SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise photometry, we present a new image differencing technique that is implemented for the first time on the ROTSE SN photometry pipeline. With this method, we find up to a 20\% increase in the detection efficiency and significant reduction in residual RMS scatter of the SN lightcurves when compared to the previous pipeline performance. We use the published optical spectra and broadband photometry of well studied SNe IIP to establish temporal models for ejecta velocity and photospheric temperature evolution for our SNe IIP population. This study yields measurements that are competitive to other methods even when the data are limited to a single epoch during the photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and optical spectra, we apply these models to the respective photometric epochs for each SN in the ROTSE IIP sample. This facilitates the use of the Expanding Photosphere Method (EPM) to obtain distance estimates to their respective host galaxies. We then perform cosmological parameter fitting using these EPM distances from which we measure the Hubble constant to be $72.9^{+5.7}_{-4.3}~{\rm kms^{-1}~Mpc^{-1}}$, which is consistent with the standard $\Lambda CDM$ model values derived using other independent techniques.Comment: 19 pages, 13 figure

Direct-to-Consumer and Physician Promotion of Tegaserod Correlated With Physician Visits, Diagnoses, and Prescriptions

Direct to consumer advertisement (DTCA) and physician promotion of drugs can influence patient and physician behaviors. We sought to determine the relationship between promotion of tegaserod and the number of office visits for abdominal pain, constipation, and bloating; diagnoses of irritable bowel syndrome (IBS); and tegaserod prescriptions

CPT and Lorentz tests with muons

Precision experiments with muons are sensitive to Planck-scale CPT and Lorentz violation that is undetectable in other tests. Existing data on the muonium ground-state hyperfine structure and on the muon anomalous magnetic moment could be analyzed to provide dimensionless figures of merit for CPT and Lorentz violation at the levels of $4\times 10^{-21}$ and $10^{-23}$.Comment: 4 pages, accepted for publication in Physical Review Letter

DXA Utilization Between 2006 and 2012 in Commercially Insured Younger Postmenopausal Women

Reimbursement for dual energy x-ray absorptiometry (DXA) scans in the outpatient setting has declined significantly since 2006. Research through 2011 has suggested reimbursement reductions for DXA scans have corresponded with an overall decreased utilization of DXA. This study updates utilization estimates for DXAs through 2012 in patients with commercial insurance and compares DXA rates before and after reimbursement changes