Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of T_{K}∼480  K. We report a negative in-plane thermal expansion α/T below 2 K, which passes through a broad minimum near 0.75 K. Volume and a-axis magnetostriction for B∥a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6 T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1 K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T≪T_{K} result from geometrical frustration.

Magnetic structure and crystal field excitations of NdOs2Al10: a neutron scattering study

We have investigated the magnetic properties of a polycrystalline sample of NdOs₂Al₁₀using neutron diffraction and inelastic neutron scattering, magnetic susceptibility and heat capacity measurements. The magnetic susceptibility data reveal an antiferromagnetic transition atT_N1= 2.2 K while the heat capacity data which extend to lower temperatures show a further transition atT_N2= 1.1 K. The INS measurements detect four well-resolved crystal field excitations at 7.4, 12.4, 17.6 meV and 19.2 meV at 5 K. The positions and intensities of the observed CEF excitations and the temperature dependence of previously published single crystal susceptibility data are analysed based on the orthorhombic CEF model of theJ= 9/2 ground state multiplet of Nd³⁺ion. The neutron diffraction study reveals the magnetic structure atT= 1.6 K to be of sine wave type (κ= [0, 0.723, 0]) with an ordered state moment ofμ_Nd³⁺= 1.59(1)μ_Baligned along thea-axis in agreement with the single ion crystal field anisotropy. This indicates that the magnetism of NdOs₂Al₁₀is governed by the RKKY interactions in agreement with otherRT₂Al₁₀(R= Nd, Sm, Tb,T= Fe, Ru and Os), but different to that ofR= Ce based compounds where anisotropic two ions interaction as well as Kondo interaction govern the anomalous direction of the ordered state moment.

Static and dynamic structures of liquid Ba8Ga16Sn30: a melt of the thermoelectric clathrate compounds

X-ray diffraction and inelastic x-ray scattering measurements of liquid Ba₈Ga₁₆Sn₃₀ have been carried out to investigate local structure and atomic dynamics in the liquid. The pair distribution function shows shorter and longer interatomic distances in the first coordination shell. The dynamic structure factor exhibits the inelastic excitations on both sides of the quasielastic central peak. The inelastic excitations disperse with increasing the momentum transfer, suggesting the longitudinal acoustic mode. We found a low energy excitation in addition to the longitudinal acoustic excitation in the dynamic structure factor and it reminds us a strong relationship with a rattling motion of a guest (Ba) atom in the solid state. The temperature dependence of the pair distribution function and the longitudinal acoustic excitation energy is very weak in a range from 600 to 900 °C. The result suggests that Ba and other atoms in the melt are located around minimum positions of the effective pair potential approximated as a harmonic one.

Single-Site Non-Fermi-Liquid Behaviors in a Diluted 4f^{2} System Y_{1-x}Pr_{x}Ir_{2}Zn_{20}

Electrical resistivity ρ(T) and specific heat C(T) measurements have been made on the diluted 4f^{2} system Y(Pr)Ir_{2}Zn_{20}. Both data of ρ and magnetic specific heat C_{m} per Pr ion are well scaled as a function of T/T_{0}, where T_{0} is a characteristic temperature of non-Fermi-liquid (NFL) behaviors. Furthermore, the temperature dependences of ρ and C_{m}/T agree with the NFL behaviors predicted by the two-channel Kondo model for the strong coupling limit. Therefore, we infer that the observed NFL behaviors result from the single-site quadrupole Kondo effect due to the hybridization of the 4f^{2} states with multichannel conduction electrons.

Hard x-ray photoemission study of Yb1-x Zr x B12: the effects of electron doping on the Kondo insulator YbB12

We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb_1-x Zr _x B₁₂ ([Formula: see text]) to study the effects of electron doping on the Kondo insulator YbB₁₂. The Yb valences of Yb_1-x Zr _x B₁₂ at 300 K estimated from the Yb 3d HAXPES spectra decreased after substituting Yb with Zr from 2.93 for YbB₁₂ to 2.83 for Yb_0.125Zr_0.875B₁₂. A temperature dependent valence decrease was found upon cooling for all doping concentrations. We found peak shifts of the B 1s and Zr 3d_5/2, and Yb³⁺ 4f spectra toward the deeper binding-energy with increasing Zr concentration, which indicates a shift of the Fermi level to the higher energy and that of the Yb 4f hole level close to the Fermi level, respectively, due to electron doping. These results qualitatively show the enhanced hybridization between the Yb 4f and conduction-band states with Zr substitution, consistent with magnetic susceptibility measurements.

Nonmagnetic ground states and phase transitions in the caged compounds PrT2Zn20 (T = Ru, Rh and Ir)

We performed electrical resistivity ρ, magnetic susceptibility χ, specific heat C and electron diffraction measurements on single-crystalline samples of PrT2Zn20 (T = Ru, Rh and Ir). The three compounds show the Van Vleck paramagnetic behavior, indicating the nonmagnetic crystalline electric field (CEF) ground states. A Schottky-type peak appears at around 14 K, irrespective of the T element, which can be moderately reproduced by a doublet–triplet model. For T = Ru, a structural transition occurs at Ts = 138 K, below which no phase transition appears down to 0.04 K. On the other hand, for T = Ir, antiferroquadrupole (AFQ) ordering arising from the nonmagnetic Γ3 doublet takes place at TQ = 0.11 K. For T = Rh, despite a structural transition between 170 and 470 K, the CEF ground state is still the non-Kramers Γ3 doublet. However, no phase transition due to the Γ3 doublet was observed even down to 0.1 K.

Interplay of low-energy phonons and magnetic excitations in the Kondo insulator YbB12

Peculiarities in the lattice dynamics of the Kondo insulator Y bB(12) have been studied by inelastic neutron scattering. Selected phonon modes were traced above and below the temperature region (T ~ 50 K) where the gap opens in the electron density of states. The intensities of some low-energy modes exhibit an anomalous temperature dependence for q vectors close to the Brillouin zone boundary, suggesting a renormalization of the phonon eigenvectors. This effect is thought to arise from a coupling with magnetic excitations of the same symmetry, which exist at nearby energies. It is argued that this magnetovibrational coupling may in turn play a role in the steep temperature crossover existing in Y bB(12) between the low-temperature (Kondo insulator) and high-temperature (incoherent spin-fluctuation) regimes, which is rapidly suppressed by lighter Zr substitution.

Antiferroquadrupolar ordering in a Pr-based superconductor PrIr(2)Zn(20)

An antiferroquadrupolar ordering at T(Q)=0.11  K has been found in a Pr-based superconductor PrIr(2)Zn(20). The measurements of specific heat and magnetization revealed the non-Kramers Γ(3) doublet ground state with the quadrupolar degrees of freedom. The specific heat exhibits a sharp peak at T(Q)=0.11  K. The increment of T(Q) in magnetic fields and the anisotropic B-T phase diagram are consistent with the antiferroquadrupolar ordered state below T(Q). The entropy release at T(Q) is only 20% of Rln2, suggesting that the quadrupolar fluctuations play a role in the formation of the superconducting pairs below T(c)=0.05  K.

Optical conductivity spectral anomalies in the off-center rattling system β-Ba8Ga16Sn30

We present optical conductivity studies of the type-I clathrate Ba8Ga16Sn30, using a terahertz time-domain spectrometer (0.3-3.0 THz). The lowest-lying spectral peak at 0.72 THz due to the Ba(2) ion's off-center vibration in the oversized cage shows a drastic and anomalous temperature dependence. Below about 100 K, the single broad peak splits into two subpeaks, and with further lowering of the temperature, the spectral shape of this so-called rattling phonon shows non-Boltzmann broadening to the point that the linewidth becomes comparable to the peak frequency. Whereas the initial splitting can be understood by assuming a multiwell anharmonic potential, the strong linewidth broadening toward low temperature cannot, since the Boltzmann factor generally sharpens the low-temperature spectra. The observed behavior suggests strong interaction between the local anharmonic phonons and other excitations.

Multistep magnetization plateaus in the Shastry-Sutherland system TbB4

We report high-field magnetization and magnetostriction measurements on the rare-earth-metal tetraboride TbB4, in which the Tb moments form a Shastry-Sutherland lattice in the tetragonal basal plane. A number of magnetization plateaus appear when the magnetic field is perpendicular to the magnetic easy plane. We propose that the magnetization plateaus arise from the combined effect of magnetic frustration and quadrupole interaction in the unique two-dimensional network.

Off-center rattling and anisotropic expansion of type-I clathrates studied by Raman scattering

Dynamical motions of the guest ions in type-I clathrates Sr8Ga16Si(30-x)Gex and Ba8Ga16Si(30-x)Gex have been studied by Raman scattering spectroscopy, to clarify the role of guest vibration modes in these systems with unusual thermal transport behaviors. An anomalous decrease of the guest energies with decreasing temperature is observed for both systems. The Ge-doping expands the cage surrounding the 6d site anisotropically for Sr8Ga16Si(30-x)Gex, but isotropically for Ba8Ga16Si(30-x)Gex. Especially for Sr8Ga16Si(30-x)Gex, off-center rattling arises simultaneously with the anisotropic expansion, and it is confirmed that these anomalies play a crucial role to suppress lattice thermal conductivity in these systems.

Terahertz conductivity of localized photoinduced carriers in a Mott insulator YTiO(3) at low excitation density, contrasted with the metallic nature in a band semiconductor Si

We performed optical-pump terahertz-probe measurements of a Mott insulator YTiO(3) and a band semiconductor Si using a laser diode (1.47 eV) and a femtosecond-pulse laser (1.55 eV). Both samples possess long energy-relaxation times (1.5 ms for YTiO(3) and 15 µs for Si); therefore, it is possible to extract terahertz complex conductivities of photoinduced carriers under equilibrium. We observed highly contrasting behaviour-Drude conductivity in Si and localized conductivity possibly obeying the Jonscher law in YTiO(3). The carrier number at the highest carrier-concentration layer in YTiO(3) is estimated to be 0.015 per Ti site. Anisotropic conductivity of YTiO(3) is determined. Our study indicates that localized carriers might play an important role in the incipient formation of photoinduced metallic phases in Mott insulators. In addition, this study shows that the transfer-matrix method is effective for extracting an optical constant of a sample with a spatially inhomogeneous carrier distribution.

Polarized-neutron study of spin dynamics in the Kondo insulator YbB12

Inelastic neutron scattering experiments have been performed on the archetype compound YbB(12), using neutron polarization analysis to separate the magnetic signal from the phonon background. With decreasing temperature, components characteristic for a single-site spin-fluctuation dynamics are suppressed, giving place to specific, strongly Q-dependent, low-energy excitations near the spin-gap edge. This crossover is discussed in terms of a simple crystal-field description of the incoherent high-temperature state and a predominantly local mechanism for the formation of the low-temperature singlet ground state.

Anisotropic 4f-spin dynamics across the B-T phase diagram of Ce(7)Ni(3)

Longitudinal field μSR measurements in applied fields parallel and perpendicular to the c-axis of the hexagonal heavy-fermion antiferromagnet Ce(7)Ni(3) served to monitor the 4f-spin dynamics across the magnetic phase diagram in the B-T plane, which consists of an incommensurate/commensurate antiferromagnetic (AF) section below 1.9 K/0.7 K and below an applied field B of 0.25 T, and for B along the c-axis, of a field-induced magnetic (FIM) section for B≥0.6 T and below 0.5 K. The observed μ(+) spin-lattice relaxation rates reveal persisting spin dynamics across the whole phase diagram, reflect the various phase boundaries and are interpreted to arise in the AF and FIM phases from the Ce3 sublattice (the Ce ions are located on three different sublattices) and in the intermediate phase, viewed as a short range ordered (SRO) state, also from the Ce1 and Ce2 sublattices with slower fluctuation rates. In the paramagnetic regime the Ce1 sublattice displays the slowest spin dynamics. In the FIM phase the fraction of relaxing μ(+) appears to shrink with rising B, evidencing a possible phase separation.

Magnetic-field-induced band-structure change in CeBiPt

We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above approximately 25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.

Determination of the orbital polarization in YTiO3 by using soft X-ray linear dichroism

We report measurements of linear dichroism in x-ray absorption at Ti L(2,3) edges of a Mott-insulating ferromagnet YTiO3, where orbital ordering occurs in the triply degenerate Ti 3d t(2g) states. Dichroic spectra and their integrated intensities are obtained for the incident electric field with polarizations parallel to a, b, and c axes. The comparison of the spectra with atomic multiplet calculations removes the ambiguity about the orbital polarization, i.e., the relative weights of |xy>, |yz>, and |zx> orbits, which are crucial for the origin of ferromagnetism. The result is consistent with the previous analysis of nuclear magnetic resonance in the Mizokawa-Fujimori scheme.

No lengthening of life span in mice continuously exposed to gamma rays at very low dose rates

Late effects of continuous exposure to ionizing radiation are potential hazards to workers in radiation facilities as well as to the general public. Recently, low-dose-rate and low-dose effects have become a serious concern. Using a total of 4000 mice, we studied the late biological effects of chronic exposure to low-dose-rate radiation as assayed by life span. Two thousand male and 2000 female 8-week-old specific-pathogen-free (SPF) B6C3F1 mice were randomly divided into four groups (one nonirradiated control and three irradiated). Irradiation was carried out for approximately 400 days using (137)Cs gamma rays at dose rates of 21 mGy day(-1), 1.1 mGy day(-1) and 0.05 mGy day(-1) with total doses equivalent to 8000 mGy, 400 mGy and 20 mGy, respectively. All mice were kept under SPF conditions until they died spontaneously. Statistical analyses showed that the life spans of mice of both sexes irradiated with 21 mGy day(-1) (P < 0.0001) and of females irradiated with 1.1 mGy day(-1) (P < 0.05) were significantly shorter than those of the control group. Our results show no evidence of lengthened life span in mice continuously exposed to very low dose rates of gamma rays.

[Formations and reactions of aromatic furazan compounds]

A reaction from various kinds of nitroquinoline with hydroxylamine in potassium hydroxide alkalinity produced a novel product, furazanoquinoline, besides the known amino derivatives. The products obtained were furazano [3,4-f] quinoline (5) from 5-nitroquinoline (1) and 6-nitroquinoline (6), and furazano [3,4-h] quinoline (10) from 7-nitroquinoline (8) and 8-nitroquinoline (11). The reaction mechanism was believed to be as shown in Figs. 2 and 3. The photoreaction of benzofuroxan (19) in acetonitrile containing a little water, under a high pressure mercury lamp, produced 1H-azepine-2,7-dione (20), while under irradiation using a low pressure lamp, 6H-furazano [4,5-c] carbazole-3-oxide (21) and compound 20 were obtained. Then the photoproduct 20 produced photodimer 22 by irradiation in acetonitrile: water (9:1, v/v) using a high or low pressure mercury lamp, while photolysis with alkali proceeded as in the photoreaction of N-alkylimide to give 7-hydroxy-1H-azepine-2-one (23). When pyrido [2,3-c] furoxan (24) was irradiated in acetonitrile containing a little water with a low pressure mercury lamp, 3-nitro-2-pyridone (25) was obtained. When compound 24 was irradiated in the presence of morpholine with a low pressure mercury lamp in an argon atmosphere, 6-morpholinopyridine 2,3-dioxime (26) was produced. Quinoxaline 1,4-dioxide derivatives (31, 33), phenazine 5,10-dioxide derivatives (36, 37) and pyrido [2,3-b] pyrazine derivatives (38, 39) were synthesized from the corresponding furoxan catalyzed by silica gel or molecular sieves, and their antibacterial properties were evaluated. The results of antibacterial screening tests in vitro, revealed strong activity against Bacteroides fragilis.

Redox regulation of MAPK pathways and cardiac hypertrophy in adult rat cardiac myocyte

OBJECTIVES

We analyzed the regulatory function of reactive oxygen species (ROS) on the hypertrophic signaling in adult rat cardiac myocytes:

BACKGROUND

The ROS regulate mitogenic signal transduction in various cell types. In neonatal rat cardiac myocyte, antioxidants have been shown to inhibit cardiac hypertrophy, and ROS are suggested to modulate the hypertrophic signaling. However, the conclusion may not reflect the situation of mature heart, because of the different natures between neonatal and adult cardiac myocytes.

METHODS

Cultured adult rat cardiac myocytes were stimulated with endothelin-1 (ET-1) or phenylephrine (PE), and intracellular ROS levels, the activities of mitogen-activated protein kinases (MAPKs; ERK, p38, and JNK), and 3H-phenylalanine incorporation were examined. We also examined the effects of antioxidant pretreatment of myocytes on MAPK activities and cardiac hypertrophy to analyze the modulatory function of redox state on MAPK-mediated hypertrophic signaling.

RESULTS

The ROS levels in ET-1- or PE-stimulated myocytes were maximally increased at 5 min after stimulation. The origin of ROS appears to be from NADH/NADPH oxidase, because the increase in ROS was suppressed by pretreatment of myocytes with NADH/NADPH oxidase inhibitor diphenyleneiodonium. Extracellular signal-regulated kinase (ERK) activity was increased by the stimulation of ET-1 or PE. In contrast, p38 and c-Jun-N-terminal protein kinase (JNK) activities did not change after these stimulations. Antioxidant treatment of myocytes suppressed the increase in ROS and blocked ERK activation and the subsequent cardiac hypertrophy induced by these stimuli.

CONCLUSIONS

These data demonstrate that ROS mediate signal transduction of cardiac hypertrophy induced by ET-1 or PE in adult rat cardiac myocytes.

Distinct expression of two types of Xenopus Patched genes during early embryogenesis and hindlimb development

Patched (Ptc) is a putative twelve transmembrane domain protein that is both a Hedgehog (Hh) receptor and transcriptional target of Hh. In this study, we isolated Xenopus Ptc cDNAs, Ptc-1 and Ptc-2, and carried out comparative analyses on their expression patterns. The putative Ptc-2 protein has a long C-terminal extension that has similarities in both length and sequence to those of Ptc-1 proteins in mouse, chick and human. In both early embryogenesis and hindlimb development, Ptc-2 expression is restricted to cells that receive a Hh signal, a pattern similar to that of Gli-1. Ptc-1, however, shows a broader distribution, mainly non-overlapping with that of Ptc-2. Despite the difference in their expression patterns, both are induced in animal cap explants synergistically by Shh and Noggin, showing a conserved regulation in their activation mechanisms.

Isolation and characterization of three novel serine protease genes from Xenopus laevis

Three novel cDNAs encoding serine proteases, that may play a role in early vertebrate development, have been identified from Xenopus laevis. These Xenopus cDNAs encode trypsin-like serine proteases and are designated Xenopus embryonic serine protease (Xesp)-1, Xesp-2, and XMT-SP1, a homolog of human MT-SP1. Xesp-1 is likely to be a secreted protein that functions in the extracellular space. Xesp-2 and XMP-SP1 are likely to be type II membrane proteases with multidomain structures. Xesp-2 has eight low density lipoprotein receptor (LDLR) domains and one scavenger receptor cysteine-rich (SRCR) domain, and XMT-SP1 has four LDLR domains and two CUB domains. The temporal expressions of these serine protease genes show distinct and characteristic patterns during embryogenesis, and they are differently distributed in adult tissues. Overexpression of Xesp-1 caused no significant defect in embryonic development, but overexpression of Xesp-2 or XMT-SP1 caused defective gastrulation or apoptosis, respectively. These results suggest that these proteases may play important roles during early Xenopus development, such as regulation of cell movement in gastrulae.

Distribution of dorsal-forming activity in precleavage embryos of the Japanese newt, Cynops pyrrhogaster: effects of deletion of vegetal cytoplasm, UV irradiation, and lithium treatment

Two types of axis-deficient embryos developed after deletion of the vegetal cytoplasm: wasp-shaped embryos and permanent-blastula-type embryos. In situ hybridization revealed that neither type of axis-deficient embryo expressed goosecoid or pax-6. brachyury was expressed in the constricted waist region of the wasp-shaped embryos but was not expressed in the permanent-blastula-type embryos. Further, we examined the effect of UV irradiation on Japanese newt embryos. Surprisingly, UV-irradiated Japanese newt eggs formed hyperdorsalized embryos. These embryos gastrulated in an irregular circular fashion with goosecoid expression in the circular equatorial region. At tailbud stage, these embryos formed a proboscis which is very reminiscent of that formed in hyperdorsalized Xenopus embryos. Transplantation of the marginal region of the UV-irradiated embryos revealed that the entire marginal zone had organizer activity. Thus we conclude that UV hyperdorsalizes Japanese newt embryos. Finally, lithium treatment of normal embryos at the 32-cell stage also resulted in hyperdorsalization. Lithium treatment of vegetally deleted embryos had two distinct results. Lithium treatment of permanent-blastula-type embryos did not result in the formation of dorsal axial structures, while the same treatment reinduced gastrulation and dorsal axis formation in the wasp-shaped embryos. Based on these results, we propose a model for early axis specification in Japanese newt embryos. The model presented here is fundamentally identical to the Xenopus model, with some important modifications. The vegetally located determinants required for dorsal development (dorsal determinants, DDs) are distributed over a wider region at fertilization in Japanese newt embryos than in Xenopus embryos. The marginal region of the Japanese newt embryo at the beginning of development overlaps with the field of the DDs. Gastrulation is very likely to be a dorsal marginal-specific property, while self-constriction is most probably a ventral marginal-specific property in Japanese newt embryos.

Conserved and divergent expression of T-box genes Tbx2-Tbx5 in Xenopus

We report here the identification of four members of T-box family genes, Xltbx2-Xltbx5, in Xenopus. Two of them are probable pseudovariant genes of XTbx5 and ET, a putative Xenopus ortholog of Tbx3. We compared their expression patterns in both embryos and limbs. In embryos, expression of Xltbx2 and Xltbx3 showed novel diversities, such as Xltbx2 in the neural crest cells and Xltbx3 in the ventral spinal cord, together with mutual similarities in the following regions: dorsal retina, proctoderm, lateral line organ, cement gland and cranial ganglia. The patterns in limbs were highly conserved with mouse and chick orthologs, including the limb-type specific expression of Xltbx4 and Xltbx5. In addition, RT-PCR analysis showed that they are expressed weakly even in adult limbs as previously reported in the newt.

The early expression control of Xepsin by nonaxial and planar posteriorizing signals in Xenopus epidermis

The control mechanism of the anteroposterior axis specification in Xenopus epidermis was studied by comparing the expression of a novel anterior marker, Xepsin, with that of a panepidermal marker, type I keratin. Xepsin mRNA, which encodes a novel Xenopus serine protease, is transcribed zygotically with the expression peak in neurula stages. In normal development, its expression is limited to the anterior and anterior-dorsal portions within epidermis during neurula and tailbud stages, respectively. In UV-irradiated ventralized embryos (dorsoanterior index, DAI 0 and 1), an expression boundary for Xepsin is apparently formed within the epidermis. In contrast, Xepsin expression was observed throughout the epidermis in LiCl-treated dorsalized embryos (DAI 10), as seen from an expression pattern indistinguishable from that of type I keratin. These data suggest that posteriorizing signals which suppress the transcription of Xepsin are present in nonaxial regions and absent in the anterior dorsal mesoderm. That posteriorizing signals were present in nonaxial regions was also supported by a conjugation experiment in which Xepsin expression was suppressed in ectodermal explants conjugated with lateral or ventral marginal zone. Moreover, the partly suppressed expression of Xepsin in the epidermal region of exogastrulae indicates that the signals may travel horizontally within the plane of the epidermis. We also present data showing that both treatment with retinoic acid and the overexpression of a constitutively active form of a retinoic acid receptor caused the suppression of Xepsin mRNA transcription, suggesting that anterior-posterior patterning in the central nervous system and in the epidermis may share common endogenous factors, i.e. , retinoids, in the Xenopus embryo.

Renal effects of efonidipine hydrochloride, a new calcium antagonist, in spontaneously hypertensive rats with glomerular injury

1. To obtain some insight into the renoprotective mechanism of the new calcium antagonist efonidipine hydrochloride, we evaluated the acute effects of efonidipine on proteinuria, glomerular haemodynamics and the tubuloglomerular feedback (TGF) mechanism in anaesthetized 24-25-week-old spontaneously hypertensive rats (SHR) with glomerular injury. 2. Efonidipine infusion at 10 micrograms/kg per h following a bolus dose of 10 micrograms/kg, i.v., reduced systemic blood pressure (BP) and renal vascular resistance, whereas renal plasma flow (RPF), glomerular filtration rate (GFR), filtration fraction, urine volume and urinary sodium excretion were unaltered. Urinary protein excretion was clearly diminished from 163 +/- 25 to 105 +/- 24 ng/min per g kidney weight. 3. Micropuncture experiments revealed that the maximal reduction of proximal stop-flow pressure (SFP), an index of glomerular capillary pressure (Pgc), induced by loop of Henle perfusion was significantly less with efonidipine treatment (6.7 +/- 1.0% of SFP with no loop flow) than in control (23.8 +/- 3.1%). In the presence of efonidipine, SFP at half-maximal reduction (SFP1/2max), which approximates Pgc at the in vivo steady state tubular flow rate, remained unchanged compared with control (36.9 +/- 0.8 vs 35.3 +/- 0.7 mmHg, respectively) and the slope of dependency on mean BP was not different between control and efonidipine. 4. These results indicate that efonidipine attenuates the TGF response in SHR by dilating the afferent arteriole, thus maintaining the level of RPF and GFR despite reduced renal perfusion pressure. Constant GFR and SFP1/2max under efonidipine suggest that single nephron GFR and Pgc remain unaltered and that a marked reduction in proteinuria is achieved without changes in single nephron GFR or Pgc of superficial nephrons.

Expression and secretion of a biologically active mouse sonic hedgehog protein by the methylotrophic yeast Pichia pastoris

We have successfully secreted the amino-terminal functional domain of mouse sonic hedgehog protein (SHH) into culture fluid using a yeast Pichia pastoris expression system. A cDNA fragment encoding the amino-terminal domain of mouse SHH was inserted downstream of the Saccharomyces cerevisiae alpha-mating factor secretion signal. The DNA fragment was introduced into the host genome by the spheroplast transformation method. Transformants were selected based on their resistance to G418: His+ transformants which showed resistance to over 8 mg G418/ml were selected and analyzed for determination of the plasmid copy number. One His+ clone which has eight copies of the expression cassette per genome was cultured in minimal medium deficient for histidine, and further cultured in buffered medium supplemented with methanol which activates the AOX1 promoter. SDS-PAGE analysis indicated efficient expression and secretion of mouse SHH into culture fluid. The yield of secreted SHH was estimated to be 50 micrograms/ml. Purified protein was assayed for biological activity and found to activate the transcription of the Patched genes (Ptc-1 and Ptc-2) encoding receptors for SHH.

Expression of five novel T-box genes and brachyury during embryogenesis, and in developing and regenerating limbs and tails of newts

Several T-box genes are considered to play important roles in developing limbs, tails and neural retinae. Five novel T-box genes in the Japanese newt were isolated and their expression was analyzed, together with another T-box gene of brachyury, during embryogenesis and in the developing and regenerating limbs and tail. Four are designated CpTbx2, CpTbx3, CpTbx6R and CpEomesodermin based on molecular phylogenetic analyses, and the other is named CpUbiqT from its ubiquitous expression. While all were expressed during embryogenesis, only four of them (CpTbx2, CpTbx3, CpUbiqT and brachyury) were detected in developing limbs and/or tails. Except for brachyury, they were continuously expressed in normal adult appendages and showed elevated expression levels in regenerating limbs, whereas only CpTbx2 showed significant up-regulation in regenerating tails. Compared with orthologous genes in other species, CpTbx2, CpTbx3 and CpEomesodermin showed several notable differences such as an abundance of maternal transcripts of CpEomesodermin, a unique insertion sequence within the T-box domain of CpTbx2, and a lack of visible expression of CpTbx2and CpTbx3 in the apical ectodermal region of developing limbs. In view of the uniqueness of the newt, these results are discussed with respect to the possibility of their involvement in regeneration.

A calcium antagonist protects against doxorubicin-induced impairment of calcium handling in neonatal rat cardiac myocytes

The effects of doxorubicin (DOX) on intracellular calcium transients and the cardioprotective effects of a calcium antagonist on DOX-induced impairment of calcium handling were examined in neonatal rat cultured cardiac myocytes. Cultured cardiac myocytes isolated from neonatal Wistar-Kyoto rats were treated with DOX for 24 h. Field-stimulated calcium transients in single myocytes were measured in the presence or absence of isoproterenol using fura-2/AM. Calcium transients were also measured after the addition of DOX to myocytes pretreated with a calcium antagonist, benidipine. DOX reduced the amplitude, maximum velocity of increase and decrease of calcium transients and prolonged the time course of calcium transients and impaired the beta-adrenoceptor responsiveness of calcium transients in a concentration-dependent manner. The DOX-induced impairment of calcium transients and beta-adrenoceptor responsiveness was improved by 10(-8) mol/L of benidipine. However, these improvements decreased with increasing concentrations of benidipine. DOX impaired both the mobilization and removal of intracellular calcium ions in contraction-relaxation cycles and the response of calcium transients to beta-adrenoceptor stimulation. Appropriate concentration of benidipine ameliorated DOX-induced impairment of calcium dynamics, suggesting that benidipine, a long-acting calcium antagonist, has potential clinical usefulness on DOX-induced abnormal calcium handling.

Overlapping and non-overlapping Ptch2 expression with Shh during mouse embryogenesis

In Drosophila, patched encodes a negative regulator of Hedgehog signaling. Biochemical experiments have demonstrated that vertebrate patched homologues might function as a Sonic hedgehog (Shh) receptor. In mice, two patched homologues, Ptch and Ptch2, have been identified. Sequence comparison have suggested that they might possess distinct properties in Shh signaling. In the developing tooth, hair and whisker, Shh and Ptch2 are co-expressed in the epithelium while Ptch is strongly expressed in the mesenchymal cells. We report here the chromosomal localization of Ptch2 and further analysis of Ptch2 expression. Throughout mouse development, the level of Ptch2 expression is significantly lower than that of Ptch. In early mouse embryos, Ptch and Ptch2 were found to be co-expressed in regions adjacent to Shh-expressing cells in the developing CNS. Similar to other epidermal structures, Shh and Ptch2 also show overlapping expression in the developing nasal gland and eyelids. Thus, during mouse development, Ptch2 is expressed in both Shh-producing and -nonproducing cells.

Isolation and characterization of a gene expressed mainly in the gastric epithelium, a novel member of the ep37 family that belongs to the betagamma-crystallin superfamily

EP37 family proteins are non-lens members of the betagamma-crystallin superfamily, of which expression is observed in integumental tissues of the Japanese newt, Cynops pyrrhogaster. In the present study, a gene was isolated that has high homology with ep37 and is transcribed mainly in the gastric epithelial cells and hence designated gep. The predicted amino acid sequence of the gep cDNA contains four betagamma-crystallin motifs in the N-terminal half, as is the case in the integumental EP37 proteins. Immunohistochemical analysis showed that GEP protein was mainly localized on the luminal content of the surface mucous cells of the gastric epithelium in both premetamorphic larvae and adults. In addition, GEP protein was also expressed in fundic glands after metamorphosis. Considering the fact that beta- and gamma-crystallins are evolutionarily related to stress-induced proteins, this localization suggests that GEP protein may have an evolutionarily conserved role in protection against physico-chemical stresses, such as physical abrasion and autodigestion, during assimilation.

Control of rat glomerular microcirculation by juxtaglomerular adenosine A1 receptors

The role of adenosine A1 receptors in the glomerular microcirculation and tubuloglomerular feedback (TGF) was studied in anesthetized Sprague-Dawley rats. TGF activity was assessed as the reduction in proximal tubular stop-flow pressure (SFP) on establishing orthograde perfusion of the loop of Henle with artificial tubular fluid at 40 nl/min. Administration of a selective A1 receptor antagonist, KW-3902 (0.5 microg/kg/min i.v.), increased fractional excretion of Na (FE(Na)) 4.3-fold without changing blood pressure, glomerular filtration rate, renal plasma flow, or filtration fraction. SFP in the absence of distal flow (SFP0) increased, and TGF-mediated SFP reduction was suppressed dose dependently [by 23 +/- 2% from an SFP0 of 34 +/- 1 mm Hg, by 15 +/- 4% from 36 +/- 2 mm Hg, and by 2 +/- 1% from 39 +/- 1 mm Hg during vehicle, low- and high-dose infusions (0.5 and 5.0 microg/kg/min), respectively]. Intratubular or peritubular capillary administration of 10(-4) M KW-3902 completely suppressed TGF without affecting SFP0. TGF suppression and elevation of SFP0 during systemic A1 blockade indicated vasodilation, both in the afferent arteriole and more proximal preglomerular vessels. Inhibition of tubular Na reabsorption combined with TGF suppression allowed the marked natriuresis. TGF suppression through systemic, luminal, and peritubular application of the drug suggest that juxtaglomerular apparatus A1 receptors are important in the control of glomerular microcirculation.

Doxorubicin cardiotoxicity: diastolic cardiac myocyte dysfunction as a result of impaired calcium handling in isolated cardiac myocytes

We examined intracellular calcium transients of isolated single cardiac myocytes from rats with doxorubicin (DOX)-induced cardiomyopathy with simultaneous measurement of cell motion. DOX was administered i.p. to Sprague-Dawley rats at 2.5 mg/kg once a week for 10 weeks. Field-stimulated calcium transients and simultaneous cell motion in single myocytes were measured in the presence or absence of isoproterenol using fura-2/AM. Histopathologic examination revealed slight changes. The time courses of both calcium transients and cell motion were significantly prolonged by DOX. There was a slight but not significant reduction in parameters of contractility in both calcium transients and cell motion. The beta-adrenoceptor responsiveness of both calcium transients and cell motion was not significantly impaired compared with the controls. Our data indicated that, despite the slight histologic changes in the heart in DOX-induced cardiomyopathy, impaired sequestration of intracellular free calcium ions in individual myocytes may be one factor leading to diastolic dysfunction. Monitoring of diastolic function is important to detect early cardiotoxicity caused by DOX.

Effects of lemildipine, a new calcium channel blocker, on renal microcirculation in SHR

The effects of lemildipine, a new dihydropyridine calcium channel blocker, on renal hemodynamics and the tubuloglomerular feedback (TGF) mechanism were examined in anesthetized 9- to 10-wk-old spontaneously hypertensive rats (SHR). Lemildipine, 3 micrograms.kg-1 i.v., did not reduce mean blood pressure (MBP) but tended to increase GFR and increased urinary excretion of sodium (UNaV). Filtration fraction (FF) and fractional excretion of sodium (FENa) remained unaltered. An additional dose of lemildipine, 9 micrograms.kg-1 i.v., reduced MBP and renal vascular resistance. Renal plasma flow tended to increase, and GFR was unchanged. FF significantly fell. UNaV and FENa remained at the control level. Micropuncture experiments revealed that the maximal reduction in proximal stop-flow pressure (SFP), an index of glomerular capillary hydrostatic pressure (Pgc), induced by perfusion of the loop of Henle was significantly reduced by high-dose treatment (8.8 +/- 1.3 vs. 13.7 +/- 1.9 mmHg in control). A high dose of lemildipine induced a rightward and slightly upward shift of the TGF curve; the steady-state tubular flow rate (V1/2) was increased, the maximal slope of the curve decreased, and SFP at V1/2 unaltered. A low dose of lemildipine did not affect TGF response. These results indicate that lemildipine attenuates the TGF response in SHR by dilating afferent arterioles and thereby corrects the left and downward shift of the TGF curve in SHR. In addition, the fall in FF indicates lemildipine-induced efferent arteriolar vasodilatation. Through balanced systemic and glomerular vasodilatation, lemildipine maintains the levels of Pgc and GFR in the face of reduced renal perfusion pressure.