63 research outputs found
Internal magnetic field effect on magnetoelectricity in orthorhombic crystals
We have investigated the role of the 4 moment on the magnetoelectric (ME)
effect of orthorhombic MnO (=rare earth ions). In order to clarify
the role of the 4 moment, we prepared three samples: (Eu,Y)MnO without
the 4 moment, TbMnO with the anisotropic 4 moment, and
(Gd,Y)MnO with the isotropic 4 moment. The ferroelectric behaviors of
these samples are different from each other in a zero magnetic field.
(Eu,Y)MnO and (Gd,Y)MnO show the ferroelectric polarization along
the a axis in the ground state, while TbMnO shows it along the c axis.
Such difference may arise from the influence of the anisotropic Tb 4
moment. The direction of the ferroelectric polarization of MnO is
determined by the internal magnetic field arising from the 4 moment.Comment: 2 pages, 1 figure, the proceeding of International Conference of
Magnetism, to be published in the Journal of Magnetism and Magnetic Material
Anomalous Coexistence of Ferroelectric Phases ( and ) in Orthorhombic EuYMnO () Crystals
We have investigated the magnetic and dielectric properties of orthorhombic
EuYMnO () single crystals without the presence
of the 4 magnetic moments of the rare-earth ions. In , the
magnetic-structure driven ferroelectricity is observed. The ferroelectric
transition temperature is steeply reducing with increasing . In , two ferroelectric phases ( and ) are
coexistent at low temperatures. In these phases, ferroelectricity has different
origin, which is evidenced by the distinctive poling-electric-field dependence
of electric polarization. Namely, the electric polarization along the c axis
() is easily saturated by a poling electric field, therefore is
caused by the spiral antiferromagnetic order. On the other hand, the
electric polarization along the a axis () is probably attributed to the
collinear -type antiferromagnetic order, because is unsaturated even
in a poling field of V/m.Comment: 10 pages, 4figures, to be published in Journal of the Physical
Society of Japa
The Effect of - Magnetic Coupling in Multiferroic MnO Crystals
We have established detailed magnetoelectric phase diagrams of
(EuY)TbMnO () and
(Eu,Y)GdMnO (), whose average ionic radii of
-site (: rare earth) cations are equal to that of Tb, in order to
reveal the effect of rare earth 4 magnetic moments on the magnetoelectric
properties. In spite of the same -site ionic radii, the magnetoelectric
properties of the two systems are remarkably different from each other. A small
amount of Tb substitution on sites () totally destroys
ferroelectric polarization along the a axis (), and an increase in Tb
concentration stabilizes the phase. On the other hand, Gd substitution
() extinguishes the phase, and slightly suppresses the
phase. These results demonstrate that the magnetoelectric properties of
MnO strongly depend on the characteristics of the rare earth 4
moments.Comment: 10 pages, 5 figures Submitted to Journal of the Physical Society of
Japa
Spin chirality and electric polarization in multiferroic compounds MnO (Ho, Er)
Polarized neutron diffraction experiments have been performed on multiferroic
materials MnO (Ho, Er) under electric fields in the
ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM)
phases, where the former has the highest electric polarization and the latter
has reduced polarization. It is found that, after cooling in electric fields
down to the CM phase, the magnetic chirality is proportional to the electric
polarization. Also we confirmed that the magnetic chirality can be switched by
the polarity of the electric polarization in both the CM and LT-ICM phases.
These facts suggest an intimate coupling between the magnetic chirality and the
electric polarization. However, upon the transition from the CM to LT-ICM
phase, the reduction of the electric polarization is not accompanied by any
reduction of the magnetic chirality, implying that the CM and LT-ICM phases
contain different mechanisms of the magnetoelectric coupling.Comment: 4 pages, 2 figures. Proceedings of PNCMI2008/QuBS200
Localization and trafficking of aquaporin 2 in the kidney
Aquaporins (AQPs) are membrane proteins serving in the transfer of water and small solutes across cellular membranes. AQPs play a variety of roles in the body such as urine formation, prevention from dehydration in covering epithelia, water handling in the bloodβbrain barrier, secretion, conditioning of the sensory system, cell motility and metastasis, formation of cell junctions, and fat metabolism. The kidney plays a central role in water homeostasis in the body. At least seven isoforms, namely AQP1, AQP2, AQP3, AQP4, AQP6, AQP7, and AQP11, are expressed. Among them, AQP2, the anti-diuretic hormone (ADH)-regulated water channel, plays a critical role in water reabsorption. AQP2 is expressed in principal cells of connecting tubules and collecting ducts, where it is stored in Rab11-positive storage vesicles in the basal state. Upon ADH stimulation, AQP2 is translocated to the apical plasma membrane, where it serves in the influx of water. The translocation process is regulated through the phosphorylation of AQP2 by protein kinase A. As soon as the stimulation is terminated, AQP2 is retrieved to early endosomes, and then transferred back to the Rab 11-positive storage compartment. Some AQP2 is secreted via multivesicular bodies into the urine as exosomes. Actin plays an important role in the intracellular trafficking of AQP2. Recent findings have shed light on the molecular basis that controls the trafficking of AQP2
Differential, Phosphorylation Dependent Trafficking of AQP2 in LLC-PK1 Cells
The kidney maintains water homeostasis by modulating aquaporin 2 (AQP2) on the plasma membrane of collecting duct principal cells in response to vasopressin (VP). VP mediated phosphorylation of AQP2 at serine 256 is critical for this effect. However, the role of phosphorylation of other serine residues in the AQP2 C-terminus is less well understood. Here, we examined the effect of phosphorylation of S256, S261 and S269 on AQP2 trafficking and association with recycling pathway markers. We used LLC-PK1 cells expressing AQP2(S-D) or (S-A) phospho mutants and a 20Β°C cold block, which allows endocytosis to continue, but prevents protein exit from the trans Golgi network (TGN), inducing formation of a perinuclear AQP2 patch. AQP2-S256D persists on the plasma membrane during cold block, while wild type AQP2, AQP2-S256A, S261A, S269A and S269D are internalized and accumulate in the patch. Development of this patch, a measure of AQP2 internalization, was most rapid with AQP2-S256A, and slowest with S261A and S269D. AQP2-S269D exhibited a biphasic internalization profile with a significant amount not internalized until 150 minutes of cold block. After rewarming to 37Β°C, wt AQP2, AQP2-S261A and AQP2-S269D rapidly redistributed throughout the cytoplasm within 20 minutes, whereas AQP2-S256A dissipated more slowly. Colocalization of AQP2 mutants with several key vesicular markers including clathrin, HSP70/HSC70, EEA, GM130 and Rab11 revealed no major differences. Overall, our data provide evidence supporting the role of S256 and S269 in the maintenance of AQP2 at the cell surface and reveal the dynamics of internalization and recycling of differentially phosphorylated AQP2 in cell culture
On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective
Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher Ξ΄18O, Ξ17O, and Ξ΅54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10βs of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation
Physiology and pathophysiology of the vasopressin-regulated renal water reabsorption
To prevent dehydration, terrestrial animals and humans have developed a sensitive and versatile system to maintain their water homeostasis. In states of hypernatremia or hypovolemia, the antidiuretic hormone vasopressin (AVP) is released from the pituitary and binds its type-2 receptor in renal principal cells. This triggers an intracellular cAMP signaling cascade, which phosphorylates aquaporin-2 (AQP2) and targets the channel to the apical plasma membrane. Driven by an osmotic gradient, pro-urinary water then passes the membrane through AQP2 and leaves the cell on the basolateral side via AQP3 and AQP4 water channels. When water homeostasis is restored, AVP levels decline, and AQP2 is internalized from the plasma membrane, leaving the plasma membrane watertight again. The action of AVP is counterbalanced by several hormones like prostaglandin E2, bradykinin, dopamine, endothelin-1, acetylcholine, epidermal growth factor, and purines. Moreover, AQP2 is strongly involved in the pathophysiology of disorders characterized by renal concentrating defects, as well as conditions associated with severe water retention. This review focuses on our recent increase in understanding of the molecular mechanisms underlying AVP-regulated renal water transport in both health and disease
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