AtHKT1;1 Mediates Nernstian Sodium Channel Transport Properties in Arabidopsis Root Stelar Cells

The Arabidopsis AtHKT1;1 protein was identified as a sodium (Na+) transporter by heterologous expression in Xenopus laevis oocytes and Saccharomyces cerevisiae. However, direct comparative in vivo electrophysiological analyses of a plant HKT transporter in wild-type and hkt loss-of-function mutants has not yet been reported and it has been recently argued that heterologous expression systems may alter properties of plant transporters, including HKT transporters. In this report, we analyze several key functions of AtHKT1;1-mediated ion currents in their native root stelar cells, including Na+ and K+ conductances, AtHKT1;1-mediated outward currents, and shifts in reversal potentials in the presence of defined intracellular and extracellular salt concentrations. Enhancer trap Arabidopsis plants with GFP-labeled root stelar cells were used to investigate AtHKT1;1-dependent ion transport properties using patch clamp electrophysiology in wild-type and athkt1;1 mutant plants. AtHKT1;1-dependent currents were carried by sodium ions and these currents were not observed in athkt1;1 mutant stelar cells. However, K+ currents in wild-type and athkt1;1 root stelar cell protoplasts were indistinguishable correlating with the Na+ over K+ selectivity of AtHKT1;1-mediated transport. Moreover, AtHKT1;1-mediated currents did not show a strong voltage dependence in vivo. Unexpectedly, removal of extracellular Na+ caused a reduction in AtHKT1;1-mediated outward currents in Columbia root stelar cells and Xenopus oocytes, indicating a role for external Na+ in regulation of AtHKT1;1 activity. Shifting the NaCl gradient in root stelar cells showed a Nernstian shift in the reversal potential providing biophysical evidence for the model that AtHKT1;1 mediates passive Na+ channel transport properties

Present state and future perspectives of using pluripotent stem cells in toxicology research

The use of novel drugs and chemicals requires reliable data on their potential toxic effects on humans. Current test systems are mainly based on animals or in vitro–cultured animal-derived cells and do not or not sufficiently mirror the situation in humans. Therefore, in vitro models based on human pluripotent stem cells (hPSCs) have become an attractive alternative. The article summarizes the characteristics of pluripotent stem cells, including embryonic carcinoma and embryonic germ cells, and discusses the potential of pluripotent stem cells for safety pharmacology and toxicology. Special attention is directed to the potential application of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) for the assessment of developmental toxicology as well as cardio- and hepatotoxicology. With respect to embryotoxicology, recent achievements of the embryonic stem cell test (EST) are described and current limitations as well as prospects of embryotoxicity studies using pluripotent stem cells are discussed. Furthermore, recent efforts to establish hPSC-based cell models for testing cardio- and hepatotoxicity are presented. In this context, methods for differentiation and selection of cardiac and hepatic cells from hPSCs are summarized, requirements and implications with respect to the use of these cells in safety pharmacology and toxicology are presented, and future challenges and perspectives of using hPSCs are discussed

Numerical and experimental analysis of small scale horizontal-axis wind turbine in yawed conditions

In wind farms a considerable amount of production losses are due to the presence of wakes: therefore, in order to optimize the efficiency, many control strategies have been conceived and tested recently. Among the most important methods investigated for wind farm control, yawing seems to be one of the most effective. Anyway, this topic has mostly been treated by an energetic point of view: there is still a lack of studies focusing on yaw effects on mechanical and vibrational behavior of wind turbines. On these grounds, this work is devoted to yawed wind turbines and a comparison is conducted between experimental data, collected in wind tunnel tests on a small scale turbine, and aeroelastic numerical models. The experimental setup is composed by a 2 m diameter wind turbine equipped with accelerometers, load cells and tachometers in order to collect vibration, thrust and rotational speed data. With this arrangement, tests have been performed in a closed loop, open chamber wind tunnel, at University of Perugia. The wind turbine has been subjected to steady wind time series and its mechanical behavior has been studied for yaw angles of ±45◦, ±22.5◦ and 0◦ . As concerns simulations, two models are implemented using the FAST software by NREL and an internally developped code based on BEM theory. The simulations are performed with the same wind speed and yaw angles as the experimental wind tunnel tests. The first step of this study is comparing power and thrust coefficients from experimental tests and numerical models. Since numerical codes tend to overestimate the thrust, further studies are conducted about blade deflections, vibrations and tower shadows. The study of experimental thrust depending on the azimuth angle in different yaw configurations revealed that, for vanishing yaw angles, the thrust force has the highest oscillations. This behavior can be ascribed to tower blockage effect and blade deflections. Under this circumstance, an outlook on vibration power spectrum is accomplished. From this it can be showed that 3P (blade passing) frequency, induced by tower blockage, decreases in correspondence of higher yaw angle, demonstrating that tower blockage has a lower effect. In addition, for wind speed lower than 10 m/s at 0◦ yaw, thrust oscillations decrease because of the correspondingly lower blade deflection