A Unique Voltage Sensor Sensitizes the Potassium Channel AKT2 to Phosphoregulation

Among all voltage-gated K+ channels from the model plant Arabidopsis thaliana, the weakly rectifying K+ channel (Kweak channel) AKT2 displays unique gating properties. AKT2 is exceptionally regulated by phosphorylation: when nonphosphorylated AKT2 behaves as an inward-rectifying potassium channel; phosphorylation of AKT2 abolishes inward rectification by shifting its activation threshold far positive (>200 mV) so that it closes only at voltages positive of +100 mV. In its phosphorylated form, AKT2 is thus locked in the open state in the entire physiological voltage range. To understand the molecular grounds of this unique gating behavior, we generated chimeras between AKT2 and the conventional inward-rectifying channel KAT1. The transfer of the pore from KAT1 to AKT2 altered the permeation properties of the channel. However, the gating properties were unaffected, suggesting that the pore region of AKT2 is not responsible for the unique Kweak gating. Instead, a lysine residue in S4, highly conserved among all Kweak channels but absent from other plant K+ channels, was pinpointed in a site-directed mutagenesis approach. Substitution of the lysine by serine or aspartate abolished the “open-lock” characteristic and converted AKT2 into an inward-rectifying channel. Interestingly, phosphoregulation of the mutant AKT2-K197S appeared to be similar to that of the Kin channel KAT1: as suggested by mimicking the phosphorylated and dephosphorylated states, phosphorylation induced a shift of the activation threshold of AKT2-K197S by about +50 mV. We conclude that the lysine residue K197 sensitizes AKT2 to phosphoregulation. The phosphorylation-induced reduction of the activation energy in AKT2 is ∼6 kT larger than in the K197S mutant. It is discussed that this hypersensitive response of AKT2 to phosphorylation equips a cell with the versatility to establish a potassium gradient and to make efficient use of it

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Physiologie moléculaire du transport de K+ chez Arabidopsis thaliana. Etude du canal AKT2, un nouveau type fonctionnel de la famille shaker

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

A Shaker-like K(+) Channel with Weak Rectification Is Expressed in Both Source and Sink Phloem Tissues of Arabidopsis

RNA gel blot and reverse transcription–polymerase chain reaction experiments were used to identify a single K(+) channel gene in Arabidopsis as expressed throughout the plant. Use of the β-glucuronidase reporter gene revealed expression of this gene, AKT2/AKT3, in both source and sink phloem tissues. The AKT2/AKT3 gene corresponds to two previously identified cDNAs, AKT2 (reconstructed at its 5′ end) and AKT3, the open reading frame of the latter being shorter at its 5′ end than that of the former. Rapid amplification of cDNA ends with polymerase chain reaction and site-directed mutagenesis was performed to identify the initiation codon for AKT2 translation. All of the data are consistent with the hypothesis that the encoded polypeptide corresponds to the longest open reading frame previously identified (AKT2). Electrophysiological characterization (macroscopic and single-channel currents) of AKT2 in both Xenopus oocytes and COS cells revealed a unique gating mode and sensitivity to pH (weak inward rectification, inhibition, and increased rectification upon internal or external acidification), suggesting that AKT2 has enough functional plasticity to perform different functions in phloem tissue of source and sink organs. The plant stress hormone abscisic acid was shown to increase the amount of AKT2 transcript, suggesting a role for the AKT2 in the plant response to drought

Influence of Thermo-mechanical Effects induced by 3D Assembly on Silicon Microring Resonator

International audienceThis paper presents the impact of 3D assembly on a silicon ring resonator. Indeed, the flip-chip integration used to connect photonic and electronic circuits requires high temperatures processes. The cooling of such a structure induces thermo-mechanical stresses on silicon waveguides. A finite element modelling is proposed to theoretically quantify the stress distribution. The photo-elastic effect is then highlighted to explain the change in silicon refractive index. As a result, the ring resonance wavelength is shifted from approximately 100 pm. Performance of a WDM (wavelength division multiplexing) system could thus be highly degraded

Physical and Functional Interaction of the Arabidopsis K(+) Channel AKT2 and Phosphatase AtPP2CA

The AKT2 K(+) channel is endowed with unique functional properties, being the only weak inward rectifier characterized to date in Arabidopsis. The gene is expressed widely, mainly in the phloem but also at lower levels in leaf epiderm, mesophyll, and guard cells. The AKT2 mRNA level is upregulated by abscisic acid. By screening a two-hybrid cDNA library, we isolated a protein phosphatase 2C (AtPP2CA) involved in abscisic acid signaling as a putative partner of AKT2. We further confirmed the interaction by in vitro binding studies. The expression of AtPP2CA (β-glucuronidase reporter gene) displayed a pattern largely overlapping that of AKT2 and was upregulated by abscisic acid. Coexpression of AtPP2CA with AKT2 in COS cells and Xenopus laevis oocytes was found to induce both an inhibition of the AKT2 current and an increase of the channel inward rectification. Site-directed mutagenesis and pharmacological analysis revealed that this functional interaction involves AtPP2CA phosphatase activity. Regulation of AKT2 activity by AtPP2CA in planta could allow the control of K(+) transport and membrane polarization during stress situations

Carrier Depletion Silicon Ring Modulator Power Penalty Versus Power Coupling Coefficient

International audienceCarrier depletion ring modulators offer low power, low footprint, and high modulation speed in the perspective of future silicon photonic interconnects. However, the optical power penalty, which stands for the impact of this device on power budget, is sensitive to the ring power coupling coefficient. In this paper, we derive a relationship between the optical power and this device parameter using a simple analytical model. This model is first described and then compared to ring modulators fabricated in a 300-mm silicon photonic platform through systematic characterization of resonance depth, quality factor, and power penalty. A significant power penalty sensitivity to coupling coefficient variability as high as ∼0.6 dB/% is evaluated from this model and confirmed by measurements. The limitations of this model are also discussed

Carrier Depletion Silicon Ring Modulator Power Penalty Versus Power Coupling Coefficient

Carrier depletion ring modulators offer low power, low footprint, and high modulation speed in the perspective of future silicon photonic interconnects. However, the optical power penalty, which stands for the impact of this device on power budget, is sensitive to the ring power coupling coefficient. In this paper, we derive a relationship between the optical power and this device parameter using a simple analytical model. This model is first described and then compared to ring modulators fabricated in a 300-mm silicon photonic platform through systematic characterization of resonance depth, quality factor, and power penalty. A significant power penalty sensitivity to coupling coefficient variability as high as ∼0.6 dB/% is evaluated from this model and confirmed by measurements. The limitations of this model are also discussed