Conductive and Kinetic Properties of Connexin45 Hemichannels Expressed in Transfected HeLa Cells

Human HeLa cells transfected with mouse connexin Cx45 were used to examine the conductive and kinetic properties of Cx45 hemichannels. The experiments were carried out on single cells using a voltage-clamp method. Lowering the [Ca2+]o revealed an extra current. Its sensitivity to extracellular Ca2+ and gap junction channel blockers (18α-glycyrrhetinic acid, palmitoleic acid, heptanol), and its absence in non-transfected HeLa cells suggested that it is carried by Cx45 hemichannels. The conductive and kinetic properties of this current, I hc, were determined adopting a biphasic pulse protocol. I hc activated at positive V m and deactivated partially at negative V m. The analysis of the instantaneous I hc yielded a linear function g hc,inst = f(V m) with a hint of a negative slope (g hc,inst: instantaneous conductance). The analysis of the steady-state I hc revealed a sigmoidal function g hc,ss = f(V m) best described with the Boltzmann equation: V m,0 = −1.08mV, g hc,min = 0.08 (g hc,ss: steady-state conductance; V m, 0:V m at which g hc,ss is half-maximally activated; g hc,min: minimal conductance; major charge carriers: K+ and Cl−). The g hc was minimal at negative V m and maximal at positive V m. This suggests that Cx45 connexons integrated in gap junction channels are gating with negative voltage. I hc deactivated exponentially with time, giving rise to single time constants, τd. The function τd = f(V m) was exponential and increased with positive V m (τd = 7.6s at V m = 0mV). The activation of I hc followed the sum of two exponentials giving rise to the time constants, τa1 and τa2. The function τa1 = f(V m) and τa2 = f(V m) were bell-shaped and yielded a maximum of ≅ 0.6s at V m ≅ −20mV and ≅ 4.9s at V m ≅ 15mV, respectively. Neither τa1 = f(V m) nor τa2 = f(V m) coincided with τd = f(V m). These findings conflict with the notion that activation and deactivation follow a simple reversible reaction scheme governed by first-order voltage-dependent processe

Electronic structure of copper intercalated transition metal dichalcogenides: First-principles calculations

We report first principles calculations, within density functional theory, of copper intercalated titanium diselenides, CuxTiSe2, for values of x ranging from 0 to 0.11. The effect of intercalation on the energy bands and densities of states of the host material is studied in order to better understand the cause of the superconductivity that was recently observed in these structures. We find that charge transfer from the copper atoms to the metal dichalcogenide host layers causes a gradual reduction in the number of holes in the otherwise semi-metallic pristine TiSe2, thus suppressing the charge density wave transition at low temperatures, and a corresponding increase in the density of states at the Fermi level. These effects are probably what drive the superconducting transition in the intercalated systems.Comment: 8 pages, 6 figure

The atomic orbitals of the topological atom

The effective atomic orbitals have been realized in the framework of Bader’s atoms in molecules theory for a general wavefunction. This formalism can be used to retrieve from any type of calculation a proper set of orthonormalized numerical atomic orbitals, with occupation numbers that sum up to the respective Quantum Theory of Atoms in Molecules (QTAIM) atomic populations. Experience shows that only a limited number of effective atomic orbitals exhibit significant occupation numbers. These correspond to atomic hybrids that closely resemble the core and valence shells of the atom. The occupation numbers of the remaining effective orbitals are almost negligible, except for atoms with hypervalent character. In addition, the molecular orbitals of a calculation can be exactly expressed as a linear combination of this orthonormalized set of numerical atomic orbitals, and the Mulliken population analysis carried out on this basis set exactly reproduces the original QTAIM atomic populations of the atoms. Approximate expansion of the molecular orbitals over a much reduced set of orthogonal atomic basis functions can also be accomplished to a very good accuracy with a singular value decomposition procedure

Feasibility of using neutron radiography to inspect the Space Shuttle solid rocket booster aft skirt, forward skirt and frustum. Part 1: Summary report

The space shuttle's solid rocket boosters (SRB) include components made primarily of aluminum that are parachuted back for retrieval from the ocean and refurbished for repeated usage. Nondestructive inspection methods used on these aging parts to reduce the risk of unforeseen problems include x-ray, ultrasonics, and eddy current. Neutron radiography tests on segments of an SRB component show that entrapped moisture and naturally occurring aluminum corrosion can be revealed by neutron radiography even if present in only small amounts. Voids in sealant can also be evaluated. Three alternatives are suggested to follow-up this study: (1) take an SRB component to an existing neutron radiography system; (2) take an existing mobile neutron radiography system to the NASA site; or (3) plan a dedicated system custom designed for NASA applications

Topology of the Spin-polarized Charge Density in bcc and fcc Iron

We investigate the topology of the spin-polarized charge density in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, in some cases the spin-polarized densities are characterized by unique topologies; for example, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical of any known for non-magnetic materials. In these cases, the two spin-densities are correlated: the spin-minority electrons have directional bond paths with deep minima in the minority density, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of two distinct spin topologies suggests that a well-known magnetic phase transition in iron can be fruitfully reexamined in light of these topological changes. We show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter also involves a topological catastrophe.Comment: 5 pages, 3 figures. Phys. Rev. Lett. (in press

Beyond the local approximation to exchange and correlation: the role of the Laplacian of the density in the energy density of Si

We model the exchange-correlation (XC) energy density of the Si crystal and atom as calculated by variational Monte Carlo (VMC) methods with a gradient analysis beyond the local density approximation (LDA). We find the Laplacian of the density to be an excellent predictor of the discrepancy between VMC and LDA energy densities in each system. A simple Laplacian-based correction to the LDA energy density is developed by means of a least square fit to the VMC XC energy density for the crystal, which fits the homogeneous electron gas and Si atom without further effort.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Window-based Streaming Graph Partitioning Algorithm

In the recent years, the scale of graph datasets has increased to such a degree that a single machine is not capable of efficiently processing large graphs. Thereby, efficient graph partitioning is necessary for those large graph applications. Traditional graph partitioning generally loads the whole graph data into the memory before performing partitioning; this is not only a time consuming task but it also creates memory bottlenecks. These issues of memory limitation and enormous time complexity can be resolved using stream-based graph partitioning. A streaming graph partitioning algorithm reads vertices once and assigns that vertex to a partition accordingly. This is also called an one-pass algorithm. This paper proposes an efficient window-based streaming graph partitioning algorithm called WStream. The WStream algorithm is an edge-cut partitioning algorithm, which distributes a vertex among the partitions. Our results suggest that the WStream algorithm is able to partition large graph data efficiently while keeping the load balanced across different partitions, and communication to a minimum. Evaluation results with real workloads also prove the effectiveness of our proposed algorithm, and it achieves a significant reduction in load imbalance and edge-cut with different ranges of dataset

Electronic Selection Rules Controlling Dislocation Glide in bcc Metals

The validity of the structure-property relationships governing the deformation behavior of bcc metals was brought into question with recent {\it ab initio} density functional studies of isolated screw dislocations in Mo and Ta. These existing relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the groups V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long $a/2$ screw dislocations.Comment: 4 pages, 2 figure