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The tarantula toxin GxTx detains K+ channel gating charges in their resting conformation.
Allosteric ligands modulate protein activity by altering the energy landscape of conformational space in ligand-protein complexes. Here we investigate how ligand binding to a K+ channel's voltage sensor allosterically modulates opening of its K+-conductive pore. The tarantula venom peptide guangxitoxin-1E (GxTx) binds to the voltage sensors of the rat voltage-gated K+ (Kv) channel Kv2.1 and acts as a partial inverse agonist. When bound to GxTx, Kv2.1 activates more slowly, deactivates more rapidly, and requires more positive voltage to reach the same K+-conductance as the unbound channel. Further, activation kinetics are more sigmoidal, indicating that multiple conformational changes coupled to opening are modulated. Single-channel current amplitudes reveal that each channel opens to full conductance when GxTx is bound. Inhibition of Kv2.1 channels by GxTx results from decreased open probability due to increased occurrence of long-lived closed states; the time constant of the final pore opening step itself is not impacted by GxTx. When intracellular potential is less than 0 mV, GxTx traps the gating charges on Kv2.1's voltage sensors in their most intracellular position. Gating charges translocate at positive voltages, however, indicating that GxTx stabilizes the most intracellular conformation of the voltage sensors (their resting conformation). Kinetic modeling suggests a modulatory mechanism: GxTx reduces the probability of voltage sensors activating, giving the pore opening step less frequent opportunities to occur. This mechanism results in K+-conductance activation kinetics that are voltage-dependent, even if pore opening (the rate-limiting step) has no inherent voltage dependence. We conclude that GxTx stabilizes voltage sensors in a resting conformation, and inhibits K+ currents by limiting opportunities for the channel pore to open, but has little, if any, direct effect on the microscopic kinetics of pore opening. The impact of GxTx on channel gating suggests that Kv2.1's pore opening step does not involve movement of its voltage sensors
Conditions for one-dimensional supersonic flow of quantum gases
One can use transsonic Bose-Einstein condensates of alkali atoms to establish
the laboratory analog of the event horizon and to measure the acoustic version
of Hawking radiation. We determine the conditions for supersonic flow and the
Hawking temperature for realistic condensates on waveguides where an external
potential plays the role of a supersonic nozzle. The transition to supersonic
speed occurs at the potential maximum and the Hawking temperature is entirely
determined by the curvature of the potential
A String Approximation for Cooper Pair in High-T superconductivity
It is assumed that in some sense the High-T superconductivity is similar
to the quantum chromodynamics (QCD). This means that the phonons in High-T
superconductor have the strong interaction between themselves like to gluons in
the QCD. At the experimental level this means that in High-T superconductor
exists the nonlinear sound waves. It is possible that the existence of the
strong phonon-phonon interaction leads to the confinement of phonons into a
phonon tube (PT) stretched between two Cooper electrons like a hypothesized
flux tube between quark and antiquark in the QCD. The flux tube in the QCD
brings to a very strong interaction between quark-antiquark, the similar
situation can be in the High-T superconductor: the presence of the PT can
essentially increase the binding energy for the Cooper pair. In the first rough
approximation the PT can be approximated as a nonrelativistic string with
Cooper electrons at the ends. The BCS theory with such potential term is
considered. It is shown that Green's function method in the superconductivity
theory is a realization of discussed Heisenberg idea proposed by him for the
quantization of nonlinear spinor field. A possible experimental testing for the
string approximation of the Cooper pair is offered.Comment: Essential changes: (a) the section is added in which it is shown that
Green's function method in the superconductivity theory is a realization of
discussed Heisenberg quantization method; (b) Veneziano amplitude is
discussed as an approximation for the 4-point Green's function in High-T_c;
(c) it is shown that Eq.(53) has more natural solution on the layer rather
than on 3 dimensional spac
The high-lying Li levels at excitation energy around 21 MeV
The H+He cluster structure in Li was investigated by the
H(,H He)n kinematically complete experiment at the incident
energy = 67.2 MeV. We have observed two resonances at =
21.30 and 21.90 MeV which are consistent with the He(H, )Li
analysis in the Ajzenberg-Selove compilation. Our data are compared with the
previous experimental data and the RGM and CSRGM calculations.Comment: 12 pages, 6 figures. Accepted for publication in J. Phys. Soc. Jp
The two-fluid model with superfluid entropy
The two-fluid model of liquid helium is generalized to the case that the
superfluid fraction has a small entropy content. We present theoretical
arguments in favour of such a small superfluid entropy. In the generalized
two-fluid model various sound modes of HeII are investigated. In a
superleak carrying a persistent current the superfluid entropy leads to a new
sound mode which we call sixth sound. The relation between the sixth sound and
the superfluid entropy is discussed in detail.Comment: 22 pages, latex, published in Nuovo Cimento 16 D (1994) 37
Spin picture of the one-dimensional Hubbard model: Two-fluid structure and phase dynamics
We propose a scheme for investigating the quantum dynamics of interacting
electron models by means of time-dependent variational principle and spin
coherent states of space lattice operators. We apply such a scheme to the
one-dimensional hubbard model, and solve the resulting equations in different
regimes. In particular, we find that at low densities the dynamics is mapped
into two coupled nonlinear Schroedinger equations, whereas near half-filling
the model is described by two coupled Josephson junction arrays. Focusing then
to the case in which only the phases of the spin variables are dynamically
active, we examine a number of different solutions corresponding to the
excitations of few macroscopic modes. Based on fixed point equation of the
simpler among them, we show that the standard one-band ground state phase space
is found.Comment: 10 pages, 1 figure, to appear on Phys. Rev.
Expression and localisation of c-kit and KITL in the adult human ovary
The c-kit/kit ligand (KITL) signalling axis is an essential component of ovarian folliculogenesis in mammals, but little is known about expression and localisation of its key components in the ovaries of reproductive age women. This study aimed to characterise mRNA expression of c-kit and KITL isoforms and the localisation of c-kit and KITL proteins in adult human premenopausal ovaries.This study utilised granulosa cells obtained from the preovulatory follicles of women undergoing assisted reproduction, pieces of ovarian tissue obtained from premenopausal women undergoing gynaecological surgeries and archival paraffin-embedded premenopausal ovarian tissues. Methodology included PCR for gene expression and Western blot or immunohistochemistry for protein expression.Both c-kit mRNA isoforms, known as GNNK+ and GNNK-, were detected in human ovarian cortex, while KITL protein isoforms (KITL1 and KITL2) were present in ovarian cortex and human granulosa cells. Immunohistochemistry showed expression of KITL and c-kit protein in multiple cell types within follicles throughout development, from primordial follicles to large antral follicles, in addition to atretic follicles. Oocytes of all follicle stages expressed c-kit protein exclusively. Interestingly, unlike animal models, expression of both proteins displayed a less cell-type specific distribution with immunostaining present in granulosa, theca and stromal cells, suggesting that autocrine signalling occurs within the human ovary.The results of this study indicate that c-kit/KITL signalling also occurs in the human ovary, as established in various animal models, and may involve previously unknown autocrine signalling.Astrud R Tuck, Rebecca L Robker, Robert J Norman, Wayne D Tilley and Theresa E Hicke
Sexual and Reproductive Health Disparities in a National Sample of Hispanic and Non-Hispanic White U.S. College Students
Hispanic students are the fastest growing minority population on U.S. college campuses. The purpose of this study was to examine differences in the sexual and reproductive health behaviors and outcomes between Hispanic and non-Hispanic White college students. Analyses utilized data from 15,518 non-married undergraduates (aged 18-24 years) responding to the Fall 2009 American College Health Association-National College Health Assessment II, a national sample of U.S. college students. Binary logistic regression analyses were used to examine disparities in sexual and reproductive health behaviors and outcomes, including sexual behavior, contraceptive and condom use, HIV testing, and STD and unintended pregnancy history, between Hispanic and non-Hispanic Whites. Hispanics had greater odds of reporting a past-year STD, although rates of reported sexual risk behaviors were no higher among Hispanics compared with non-Hispanic Whites. Compared to non-Hispanic Whites, fewer Hispanics reported using birth control pills. Hispanics were 2.5 times less likely to report using any method to prevent pregnancy, which may explain why Hispanics were more likely to report emergency contraceptive use in the past 12 months and a past-year unintended pregnancy. Important sexual health disparities exist among U.S. students, which have important practical implications for college health policy, practice, and intervention. Further research is warranted to understand the ethnic differences in the use of both hormonal and emergency contraceptives, particularly among college students
Is Cu instability during the CO<inf>2</inf>reduction reaction governed by the applied potential or the local CO concentration?
Cu-based catalysts have shown structural instability during the electrochemical CO2reduction reaction (CO2RR). However, studies on monometallic Cu catalysts do not allow a nuanced differentiation between the contribution of the applied potential and the local concentration of CO as the reaction intermediate since both are inevitably linked. We first use bimetallic Ag-core/porous Cu-shell nanoparticles, which utilise nanoconfinement to generate high local CO concentrations at the Ag core at potentials at which the Cu shell is still inactive for the CO2RR. Usingoperandoliquid cell TEM in combination withex situTEM, we can unequivocally confirm that the local CO concentration is the main source for the Cu instability. The local CO concentration is then modulated by replacing the Ag-core with a Pd-core which further confirms the role of high local CO concentrations. Product quantification during CO2RR reveals an inherent trade-off between stability, selectivity and activity in both systems
On the Rapid Collapse and Evolution of Molecular Clouds
Stars generally form faster than the ambipolar diffusion time, suggesting
that several processes short circuit the delay and promote a rapid collapse.
These processes are considered here, including turbulence compression in the
outer parts of giant molecular cloud (GMC) cores and GMC envelopes, GMC core
formation in an initially supercritical state, and compression-induced
triggering in dispersing GMC envelopes. The classical issues related to star
formation timescales are addressed: high molecular fractions, low efficiencies,
long consumption times for CO and HCN, rapid GMC core disruption and the lack
of a stable core, long absolute but short relative timescales with accelerated
star formation, and the slow motions of protostars. We consider stimuli to
collapse from changes in the density dependence of the ionization fraction, the
cosmic ray ionization rate, and various dust properties at densities above
~10^5 cm^{-3}. We favor the standard model of subcritical GMC envelops and
suggest they would be long lived if not for disruption by rapid star formation
in GMC cores. The lifecycle of GMCs is illustrated by a spiral arm section in
the Hubble Heritage image of M51, showing GMC formation, star formation, GMC
disruption with lingering triggered star formation, and envelope dispersal.
There is no delay between spiral arm dustlanes and star formation; the
classical notion results from heavy extinction in the dust lane and triggered
star formation during cloud dispersal. Differences in the IMF for the different
modes of star formation are considered.Comment: 46 pages, 5 figures, scheduled for ApJ 668, October 20, 200
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