Protein Tyrosine Phosphatase-1B (PTP-1B) Knockdown Improves Palmitate-Induced Insulin Resistance in C2C12 Skeletal Muscle Cells

Insulin resistance is the central defect in type 2 diabetes and obesity. During the development of insulin resistance a lipid accumulation is accompanied by increased PTP-1B expression in the muscle. The aim of this study was to examine the effects of PTP-1B knockdown on insulin signaling and insulin resistance in the presence or absence of palmitate in C2C12 skeletal muscle cells. A stable C2C12 cell line was established using short hairpin RNA (shRNA) to knockdown protein expression of PTP1B. Analysis of PTP-1B protein expression and phosphorylation and protein levels of IRS-1 and Akt were detected by western blot. The effects of PTP-1B knockdown on the glucose uptake was also measured in C2C12 cells. The stable C2C12 cell line harboring the PTP-1B shRNA showed 62% decrease in the PTP-1B protein levels. 0.5 mM palmitate significantly induced insulin resistance in both control (26%) and PTP-1B knockdown cells (16.5%) compared to the untreated cells. Under treatment with palmitate, insulin stimulated phosphorylation of IRS-1 (Tyr632) and Akt (Ser473) in knockdown cells was significantly 1.55- and 1.86-fold, respectively, greater than the controls. In the presence of palmitate, insulin dependent glucose uptake was significantly about 3-fold higher in PTP-1B knockdown stable C2C12 cells compared to the control cells. Our data showed that decreasing the PTP-1B protein level by shRNA can enhance the activity of important elements of insulin signaling. The improvement in insulin action persisted even in palmitate treated insulin resistant myotubes.     

Effects of External Resonant Fields on the Tokamak Edge Plasma Fluctuations

In this contribution, the effects of external resonant electric and magnetic fields on the tokamak edge plasma fluctuations have been investigated. For this purpose, the radial and poloidal electric fields and ion saturation current have been measured by two arrays of the Langmuir probes. An external resonant electric field was applied with the limiter biasing system. The biased electric voltage has been restricted to 0 < V _bias  < +320 and it has been applied with the limiter that is fixed in the r/a = 0.9. Moreover, the power spectra of particle flux Γ _r , Γ _p , Reynolds stress, coherency between E _p and I _s have been calculated. Fourier-based techniques have been employed to analyze the frequency of the Reynolds stress and particle flux. The results show that after positive biasing application (V _bias  = +200v), the Reynolds stress increases about 50 % while it doesn’t change remarkability after positive biasing with V _bias  = +320v. The Reynolds stress power spectrum confirms these results. The effect of positive biasing on Γ _r has been displayed a decrease about 60, 20 % by V _bias  = +200v, V _bias  = +320v respectively. Γ _p and I _s increase about 30 and 4 % in the present of biased (V _bias  = +200v) while they don’t change remarkability in another voltage. The power spectrum of Γ _r decreases about 15 and 10 % while the power spectrum of Γ _p increases about 80 and 20 % after positive biasing (V _bias  = +200v, V _bias  = +320v). Consequently, a better confinement obtained for biased with V _bias  = +200v. It means that, the magnitude of biased is important factor in modifying and control plasma turbulence. Also, results were compared with the effects of external resonant magnetic field.     

Estimating Time Dependence of Edge Plasma Turbulence in IR-T1 Tokamak

Time dependence of edge plasma turbulence was investigated in the IR-T1 tokamak. Time dependence of fluctuation level and spectra were measured using Langmuir probe in the region r/a = 0.8–1. In all times of typical shot, the edge plasma was turbulently unstable, with a broad band fluctuation spectrum in the range of frequencies f = 10–1000 kHz. The relative fluctuation level as monitored by the ion saturation current J⁺ was very high, in the range ?0.1–0.6 all over the time, while the fluctuation power spectra were roughly invariant in shape.     

Effects of Alfvenic Poloidal Flow and External Vertical Field on Plasma Position in IR-T1 Tokamak

We analyzed dynamic equilibrium properties of a large aspect ratio and low Beta tokamaks, in particular deriving a modified relation for the Shafranov shift in the presence of poloidal flow and external vertical field, and demonstrate it experimentally on the IR-T1 tokamak. Poloidal flow can produce modifications in the equilibrium properties. By increasing Alfvenic Mach number from zero, flow produce outward force, and plasma shifted in outward direction. If the poloidal Alfvenic Mach number equal to one, singularity will observe in the solution of generalized Grad–Shafranov equation. Also inversion of Shafranov shift in the transition of flow speed between sub-Alfvenic to super-Alfvenic speeds can be observed due to inward force produced by flow.     

Comparative Measurements of the Asymmetry Factor in Tokamaks Using the Magnetic Probes,Poloidal and Toroidal Flux Loops

Measurement of the Asymmetry factor (Shafranov parameter) is essential in tokamak plasma experiments. The purpose of this paper is comparing of the magnetic probes, poloidal flux loops, and diamagnetic loops techniques in determination of the Asymmetry factor in tokamaks. For this reason, array of magnetic probes, flux loops, and diamagnetic loop with its compensation coil, were designed, constructed, and installed on outer surface of the IR-T1 tokamak chamber, and then the Asymmetry factor and poloidal beta measured. Moreover, a few approximate values of the internal inductance for the different plasma current density profiles are also calculated. Experimental results compared.     

Biasing Effect on the Edge Plasma Electrical Fluctuations in IR-T1 Tokamak

The effect of biasing on the edge plasma electrical fluctuations and their control was investigated. Biasing was applied to both positive and negative polarity in the range of +380 to ?380 V. As soon as biasing was applied, the electrical fluctuations, fluctuations frequency and H_α emission reduced significantly and all of them showed the positive effect of biasing in the edge plasma electrical fluctuations reduction. Experiments also showed that positive biasing is more effective than negative biasing.