The stoichiometry of P2X2/6 receptor heteromers depends on relative subunit expression levels

Fast synaptic transmission involves the operation of ionotropic receptors, which are often composed of at least two types of subunit. We have developed a method, based on atomic force microscopy imaging to determine the stoichiometry and subunit arrangement within ionotropic receptors. We showed recently that the P2X(2) receptor for ATP is expressed as a trimer but that the P2X(6) subunit is unable to oligomerize. In this study we addressed the subunit stoichiometry of heteromers containing both P2X(2) and P2X(6) subunits. We transfected tsA 201 cells with both P2X(2) and P2X(6) subunits, bearing different epitope tags. We manipulated the transfection conditions so that either P2X(2) or P2X(6) was the predominant subunit expressed. By atomic force microscopy imaging of isolated receptors decorated with antiepitope antibodies, we demonstrate that when expression of the P2X(2) subunit predominates, the receptors contain primarily 2 x P2X(2) subunits and 1 x P2X(6) subunit. In contrast, when the P2X(6) subunit predominates, the subunit stoichiometry of the receptors is reversed. Our results show that the composition of P2X receptor heteromers is plastic and dependent on the relative subunit expression levels. We suggest that this property of receptor assembly might introduce an additional layer of subtlety into P2X receptor signaling

Goal driven optimization of process parameters for maximum efficiency in laser bending of advanced high strength steels

Laser forming or bending is fast becoming an attractive option for the forming of advanced high strength steels (AHSS), due primarily to the reduced formability of AHSS when compared with conventional steels in traditional contact-based forming processes. An inherently iterative process, laser forming must be optimized for efficiency in order to compete with contact based forming processes; as such, a robust and accurate method of optimal process parameter prediction is required. In this paper, goal driven optimization is conducted, utilizing numerical simulations as the basis for the prediction of optimal process parameters for the laser bending of DP 1000 steel. A key consideration of the optimization process is the requirement for minimal microstructural transformation in automotive grade high strength steels such as DP 1000

Calculation of Dielectric Susceptibility for Complex Ionic Systems: Application to a Predicted Superlattice

The Gordon-Kim theory of interionic interactions between closed-shell ions, which has had considerable success for existing alkali halide systems, has been applied to the determination of the structure, phonon dispersion, and room-temperature dielectric properties of a proposed superlattice, RbF(NaC1)2, of alkali halides. The dielectric properties of such a hypothetical material can have an unusually strong low-frequency dependence because of the presence of Brillouin-zonefolded infrared”-active modes. In evaluating the standard expressions for the dielectric properties, in the rigid-ion approximation, we make use of standard cubic and quartic anharmonic terms in addition to the instantaneous-phonon cubic anharmonic term, which is needed because of the lack of a center of inversion. Our procedure for numerically calculating the absorption for complex materials is described in detail. Effects of off-diagonal terms in the Green\u27s function and of the long-range ionic Coulomb interactions are examined. In particular, an absorption peak at 30 cm-1 is found to be especially sensitive to these contributions. This paper demonstrates (a) the theoretical existence of metastable phases of an alkali halide superlattice and (b) the application of anharmonic perturbation theory to determine the dielectric response in the infrared and millimeter-wave region for such complex materials. The particular structure studied is just one of many possibilities in this class of materials, which offers the opportunity for joint theoretical and experimental research to fabricate structures with properties tailored for specific applications

Positron annihilation studies of the AlOₓ/SiO₂/Si interface in solar cell structures

Film and film/substrate interfacecharacteristics of 30 and 60 nm-thick AlOₓfilmsgrown on Si substrates by thermal atomic layer deposition(ALD), and 30 nm-thick AlOₓfilms by sputtering, have been probed using variable-energy positron annihilation spectroscopy (VEPAS) and Doppler-broadened spectra ratio curves. All samples were found to have an interface which traps positrons, with annealing increasing this trapping response, regardless of growth method. Thermal ALD creates an AlOₓ/SiOₓ/Si interface with positron trapping and annihilation occurring in the Si side of the SiOₓ/Si boundary. An induced positive charge in the Si next to the interface reduces diffusion into the oxides and increases annihilation in the Si. In this region there is a divacancy-type response (20 ± 2%) before annealing which is increased to 47 ± 2% after annealing.Sputtering seems to not produce samples with this same electrostatic shielding; instead, positron trapping occurs directly in the SiOₓinterface in the as-deposited sample, and the positron response to it increases after annealing as an SiO₂ layer is formed. Annealing the film has the effect of lowering the film oxygen response in all film types. Compared to other structural characterization techniques, VEPAS shows larger sensitivity to differences in film preparation method and between as-deposited and annealed samples.T-T.A.L., S.R., and A.C. acknowledge funding from the Australian Research Council

AFM imaging reveals the assembly of a P2X receptor complex containing P2X2, P2X4 and P2X6 subunits

Seven P2X purinergic receptor subunits have been identified: P2X1-P2X7. All except P2X6 assemble as homotrimers, and six heteromeric receptors (P2X1/2, P2X1/4, P2X1/5, P2X2/3, P2X2/6 and P2X4/6) have been described. In addition, P2X4 homomers associate with P2X2 or P2X7 homomers as dimers of trimers. The various P2X receptors show individual functional properties, suggesting distinct physiological roles. The overlapping expression of P2X2, P2X4 and P2X6 subunits has been shown in different cell types, and functional analysis of P2X receptors in Leydig cells suggests that the three subunits interact