Sucrose- and H+-dependent charge movements associated with the gating of sucrose transporter ZmSUT1

Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (Cm). In addition to sucrose Cm was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these Cm changes, presteady-state currents (Ipre) of ZmSUT1 transport were analyzed. Decay of Ipre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to Ipre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed Cm changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/τ) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions: Taken together our results indicate that in the absence of sucrose, ‘trapped’ protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to Cm changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents

On the Interaction of Neomycin with the Slow Vacuolar Channel of Arabidopsis thaliana

This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo

The human two-pore channel 1 is modulated by cytosolic and luminal calcium

Two-pore channels (TPC) are intracellular endo-lysosomal proteins with only recently emerging roles in organellar signalling and involvement in severe human diseases. Here, we investigated the functional properties of human TPC1 expressed in TPC-free vacuoles from Arabidopsis thaliana cells. Large (20 pA/pF) TPC1 currents were elicited by cytosolic addition of the phosphoinositide phosphatidylinositol-(3,5)-bisphosphate (PI(3,5)P2) with an apparent binding constant of 3c15 nM. The channel is voltage-dependent, activating at positive potentials with single exponential kinetics and currents are Na+selective, with measurable but low permeability to Ca2+. Cytosolic Ca2+modulated hTPC1 in dual way: low \u3bcM cytosolic Ca2+increased activity by shifting the open probability towards negative voltages and by accelerating the time course of activation. This mechanism was well-described by an allosteric model. Higher levels of cytosolic Ca2+induced a voltage-dependent decrease of the currents compatible with Ca2+binding in the permeation pore. Conversely, an increase in luminal Ca2+decreased hTPC1 activity. Our data point to a process in which Ca2+permeation in hTPC1 has a positive feedback on channel activity while Na+acts as a negative regulator. We speculate that the peculiar Ca2+and Na+dependence are key for the physiological roles of the channel in organellar homeostasis and signalling

Simple Tuning Method of Virtual Synchronous Generators Reactive Control

The integration of renewable energy sources requires new control strategies to make static converters able to provide ancillary grid services, such as virtual inertia and grid support during faults. To address this issue, the idea of making inverters behave as synchronous machines is well known in the literature as the concept of Virtual Synchronous Generator. Thanks to this solution, inverters can provide both inertia and reactive grid support as traditional synchronous machines. However, the tuning of the excitation control of Virtual Synchronous Generator for proper reactive power management has not been properly analyzed in the literature. Therefore, the goal of this paper is to provide a simple tuning criterion for the VSM excitation control with improved dynamic behavior using a feed-forward term. This way, the VSM is able to provide the desired reactive support during faults and quickly track the desired reactive power setpoints. Both a theoretical analysis and experimental tests are provided for a 15 kVA system

A Detailed Analysis and Guidelines for the Induction Motor Flux-Decay Test

Ac motor drives are becoming increasingly popular in the field of industrial processes and transportation electrification. Currently, many industrial applications are based on induction machines supplied by inverters and controlled with field-oriented control techniques. Such techniques require the knowledge of the machine parameters to ensure the correctness of the torque control both in dynamic and steady-state conditions. In particular, an accurate determination of the induction motor rotor time constant is crucial. Therefore, this article analyses in detail the physical phenomena involved during the flux-decay test used for the rotor time constant determination. The reported analysis has been performed on a 15 kW induction motor. The transient of the machine's back-electromotive force (back-emf) has been critically analyzed during its evolution, finding a link between its evolution in time and the magnetic phenomena that occur both in the stator and the rotor. In particular, the effects due to the lamination saturation, the stator and rotor leakage inductances, and the stator iron losses have been associated with the transient evolution of the machine's back-emf

A Detailed Analysis of the Electromagnetic Phenomena Observed During the Flux-Decay Test

The paper analyses in detail the physical phenomena involved during the flux decay test used for the rotor time constant determination. The analysis has been performed on a 15 kW induction motor and the back e.m.f transient has been critically analysed during its evolution, finding a link between its time-by-time evolution and the physical phenomena that happen in both the stator and the rotor. In particular, the effects due to the lamination saturation, the stator and rotor leakage inductances and the stator iron losses have been associated to the transient evolution of the back e.m.f.

Redox agents regulate ion channel activity in vacuoles from higher plant cells

AbstractThe ability of redox agents to modulate certain characteristics of voltage- and calcium-activated channels has been recently investigated in a variety of animal cells. We report here the first evidence that redox agents regulate the activation of ion channels in the tonoplast of higher plants. Using the patch-clamp technique, we have demonstrated that, in tonoplasts from the leaves of the marine seagrass Posidonia oceanica and the root of the sugar beet, a variety of sulphydryl reducing agents, added at the cytoplasmic side of the vacuole, reversibly favoured the activation of the voltage-dependent slow vacuolar (SV) channel. Antioxidants, like dithiothreitol (DTT) and the reduced form of glutathione, gave a reversible increase of the voltage-activated current and faster kinetics of channel activation. Other reducing agents, such as ascorbic acid, also increased the SV currents, although to a lesser extent in comparison with DTT and glutathione, while the oxidising agent chloramine-T irreversibly abolished the activity of the channel. Single channel experiments demonstrated that DTT reversibly increased the open probability of the channel, leaving the conductance unaltered. The regulation of channel activation by glutathione may correlate ion transport with other crucial mechanisms that in plants control turgor regulation, response to oxidative stresses, detoxification and resistance to heavy metals

A Test Procedure to Evaluate Magnets Thermal Time Constant of Permanent Magnet Machines

Thanks to their high torque density, permanent magnet synchronous motors (PMSMs) currently represent the most competitive solution in the electrification processes involving transports and energy production. However, it is known how the torque production of PMSMs is strictly related to the temperature of the permanent magnets (PMs) since the latter affects control performance and efficiency. This issue thus makes necessary the thermal analysis of the machine under consideration. In this scenario, the determination of the PMs thermal time constant covers a pivotal role in implementing an accurate thermal model of PMSMs. Therefore, this paper aims at proposing an experimental test procedure to evaluate the PMs thermal time constant of PMSMs. The proposed procedure can be applied to any PMSM type without being affected by factors such as rotor lamination, shaft, and PM distribution. In this way, accurate and reliable results are obtained. The experimental validation has been carried out on four PMSMs, with different rotor structures, sizes, power, and voltage/current levels. Experimental results demonstrate the validity of the proposed method

Measurement of Rotor Thermal Time-Constant for Permanent Magnet Synchronous Machines

Thanks to their high torque density, permanent magnet synchronous motors (PMSMs) currently represent the most competitive solution in the electrification processes involving transports and energy production. However, it is known how the torque production of such motors is strictly related to the temperature of the permanent magnet (PM), affecting control performance, and efficiency. This issue makes necessary the thermal analysis of the machine, thus requiring the determination of the PM’s thermal time-constant. In this paper, an experimental method for evaluating such a parameter is proposed, allowing high accuracy and reliability of the result. The proposed procedure can be applied to any PMSM type, without being affected by factors such as rotor lamination, shaft, PM distribution. The experimental validation has been carried out on three PMSMs, having different rotor structure, sizes, and voltage/current levels. Experimental results demonstrate the validity of the proposed method

Modulation of plant TPC channels by polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are powerful modulators of several animal ion channels. It is shown here that PUFAs strongly affect the activity of the Slow Vacuolar (SV) channel encoded by the plant TPC1 gene. The patch-clamp technique was applied to isolated vacuoles from carrot taproots and Arabidopsis thaliana mesophyll cells and arachidonic acid (AA) was chosen as a model molecule for PUFAs. Our study was extended to different PUFAs including the endogenous alpha-linolenic acid (ALA). The addition of micromolar concentrations of AA reversibly inhibited the SV channel decreasing the maximum open probability and shifting the half activation voltage to positive values. Comparing the effects of different PUFAs, it was found that the length of the lipophilic acyl chain, the number of double bonds and the polar head were critical for channel modulation.The experimental data can be reproduced by a simple three-state model, in which PUFAs do not interact directly with the voltage sensors but affect the voltage-independent transition that leads the channel from the open state to the closed configuration. The results indicate that lipids play an important role in co-ordinating ion channel activities similar to what is known from animal cell