Z3 Charge Density Wave of Silicon Atomic Chains on a Vicinal Silicon Surface

An ideal one-dimensional electronic system is formed along atomic chains on Au-decorated vicinal silicon surfaces, but the nature of its low-temperature phases has been puzzling for last two decades. Here, we unambiguously identify the low-temperature structural distortion of this surface using high-resolution atomic force microscopy and scanning tunneling microscopy. The most important structural ingredient of this surface, the step-edge Si chains, are found to be strongly buckled, every third atom down, forming trimer unit cells. This observation is consistent with the recent model of rehybridized dangling bonds and rules out the antiferromagnetic spin ordering proposed earlier. The spectroscopy and electronic structure calculation indicate a charge density wave insulator with a Z₃ topology, making it possible to exploit topological phases and excitations. The tunneling current was found to substantially lower the energy barrier between three degenerate CDW states, which induces a dynamically fluctuating CDW at very low temperature.

Creation and annihilation of mobile fractional solitons in atomic chains

Localized modes in one-dimensional (1D) topological systems, such as Majonara modes in topological superconductors, are promising candidates for robust information processing. While theory predicts mobile integer and fractional topological solitons in 1D topological insulators, experiments so far have unveiled immobile, integer solitons only. Here we observe fractionalized phase defects moving along trimer silicon atomic chains formed along step edges of a vicinal silicon surface. By means of tunnelling microscopy, we identify local defects with phase shifts of 2π/3 and 4π/3 with their electronic states within the band gap and with their motions activated above 100 K. Theoretical calculations reveal the topological soliton origin of the phase defects with fractional charges of ±2e/3 and ±4e/3. Additionally, we create and annihilate individual solitons at desired locations by current pulses from the probe tip. Mobile and manipulable topological solitons may serve as robust, topologically protected information carriers in future information technology.

Molecular cloning and characterization of Amida, a novel protein which interacts with a neuron-specific immediate early gene product arc, contains novel nuclear localization signals, and causes cell death in cultured cells

Amida was isolated by the yeast two-hybrid system as a novel protein which associated with Arc, a non-transcriptional immediate early gene specific to the brain. Amida was confirmed to be associated with Arc in vitro and in vivo. Amida shows no homology to known proteins. Amida is ubiquitously expressed, although it is abundant in the brain. A transfection study revealed that Amida was localized in the nucleus and after 72 h the transfected cells underwent apoptosis. Furthermore, we found two nuclear localization signals and a domain needed for interacting with Arc was encompassed by two nuclear localization signals. Co-transfection experiment with Amida and Arc suggested that Amida transported Arc into the nucleus and negatively regulated Amida-induced cell death. These results indicate that Arc together with Amida may modulate cell death in the brain.

Inhibition by naloxone of promoter activity of the neurofilament gene in SK-N-SH cells

Chronic administration of morphine is known to decrease the levels of neurofilaments (NFs) in the ventral tegmental area. We ligated a promoter region of the mouse 68-KDa neurofilament (NF-68) gene to the pGL3-enhancer vector containing a luciferase gene, transfected it into SK-N-SH cells and then analyzed transcriptional activity in the cells treated with agonists or antagonists of opiate receptors. The activity of the NF-68 promoter was suppressed by naloxone about 55% at 10(-5) M and 30% at 10(-7) M at 48 h, but suppressed not by morphine. Naltrexone at 10(-5) M suppressed the promoter activity about 20%, but levallorphan, DAMGO, DPDPE and U50488 did not. The inhibition by naloxone was dose-dependent and not reversed by morphine. The inhibitory effect of naloxone was not observed in N18TG-2 cells and PC12 cells. Experiments with various deletion mutants revealed that a region responsible for naloxone suppression spans from -328 to -101 in the gene. These results suggest that naloxone has the ability to suppress transcriptional activity in some neurons.

A single stranded DNA-binding protein, ssCRE-BP/Pur alpha, in rat lung and its increase in allergic airway inflammation

ssCRE-BP/Pur alpha is a single stranded DNA-binding protein and may be involved in gene replication and transcription and in the development of morphine dependence. We found a ssCRE-BP/Pur alpha (45 kDa) in rat lung that was larger than those (40 kDa) identified in rat and mouse brains and mouse lung. Immunohistochemistry showed that ssCRE-BP/Pur alpha is primarily distributed in the lung epithelium. As allergic inflammation induces various gene expressions, we investigated the changes of Pur alpha during airway inflammation. Ovalbumin-sensitized rats were used for inducing allergic airway inflammation. The expression and DNA-binding activity of 45-kDa ssCRE-BP/Pur alpha were significantly increased in the sensitized rat lungs 24 hr after antigen challenge, but not in those of rats nonsensitized or sensitized with ovalbumin and challenged with saline. Immunohistochemistry and in situ hybridization demonstrated that the vascular endothelial cells and numerous infiltrated eosinophils around the airways were stained with anti-Pur alpha antibody. These data suggest that rat lung and the eosinophils contain a 45-kDa ssCRE-BP/Pur alpha that is increased when airway inflammation occurs.

Analysis of the T beta gamma-binding domain of MEKA/phosducin

MEKA/phosducin, a 33 kDa phosphoprotein in the photoreceptor cell, associates with transducin beta gamma (T beta gamma) with its N-terminal domain (N-terminal 105 amino acids of MEKA), and translocates T beta gamma from the photoreceptor disc membrane to the soluble fraction. The present study further localized the T beta gamma-binding domain to aa 17-105 of MEKA, and showed that the activity of MEKA to translocate T beta gamma depends on the domain. A series of deletion mutant MEKA proteins were prepared to investigate the domain of MEKA which binds to and translocates T beta gamma. Both binding and translocation activities were not impaired by the deletion of the N-terminal 16 amino acids of MEKA, but completely abolished by further deletion to 42Val. Although anti-MEKA serum inhibited the T beta gamma-MEKA association, the antiserum absorbed with a recombinant peptide corresponding to aa 17-105 of MEKA did not, confirming that aa 17-105 of MEKA directly interacts with T beta gamma.

Characterization of a nuclear factor that enhances DNA binding activity of SSCRE-BP/PUR alpha, a single-stranded DNA binding protein

Pur alpha has been identified as a single-stranded DNA binding protein that specifically binds to the purine-rich strand present in the DNA replication initiation zone of the human c-myc gene. We have previously demonstrated that chronic morphine treatment decreases the DNA binding activity of ssCRE-BP (single-stranded cyclic AMP response element-binding protein), which has been shown to be identical to pur alpha by cDNA cloning, and is abundant in the brain. In this report we identified an activator of ssCRE-BP/pur alpha in the brain and characterized it. Although purified ssCRE-BP/pur alpha or its GST-fusion protein exhibited very low DNA binding activities, they were markedly enhanced by including nuclear extract in the binding assay. The enhanced binding activity is trypsin-sensitive, heat-stable and has a molecular weight of approximately 66 kDa. Casein could substitute for the activator and increased the DNA binding activity of ssCRE-BP/pur alpha by one order. A series of deletion mutants were prepared in order to determine the DNA binding and activator interacting domains, and both of them were found to reside in AA 50-215 of ssCRE-BP/pur alpha. These data suggest that the DNA binding activity of ssCRE-BP/pur alpha is augmented by a nuclear protein, which may modulate the ssCRE-BP/pur alpha activity to develop morphine dependence and tolerance.

Energy metabolism in normal and hypertrophied right ventricle of the ferret heart

Using an isolated ferret heart preparation (Langendorff perfusion, perfusion pressure 90 mmHg), energy metabolism has been characterized in right and left ventricles from control and hypertrophied hearts. Hypertrophy was induced by pulmonary artery clipping for 30-45 days (right ventricle wall weight/body weight ratio increased by 70%). Myocardial contents of high energy phosphate compounds, glycogen and lactate, and the activities of some enzymes were biochemically measured in perfused hearts and also after ischemic arrest (30 min global ischemia). In hypertrophied right ventricles, PCr (-46%), Cr (-34%) levels, creatine kinase activity (-18%) were significantly decreased compared with control. ATP and Pi levels were not affected by hypertrophy. The adenylate energy charges were similar (0.85-0.86) in both types of heart. The activities of hexokinase (+26%), aldolase (+212%), pyruvate kinase (+14%) and glucose 6-phosphate dehydrogenase (+107%) were increased by hypertrophy. The LDH isozyme pattern was significantly changed such that LDH3 was decreased by 11%, and LDH4 and LDH5 were increased by a factor 1.4 and 2.9 respectively in hypertrophy. After 30 min of global ischemia, PCr level was decreased by 89 and 79% in control and hypertrophied ventricles respectively. ATP level was depressed by 41 in control and only by 21% in hypertrophied muscles. Altogether, the present data suggested that, in the adult ferret heart, the capacity for the ATP synthesis could be maintained during hypertrophy by the enhancement of the glycolytic pathway. The smaller decline of ATP after ischemia in hypertrophied tissue could be explained by a lower consumption of ATP in the hypertrophied compared to the control heart during the earliest period of ischemia.

Involvement of a single-stranded DNA binding protein, ssCRE-BP/Pur alpha, in morphine dependence

We have purified a nuclear protein from mouse cerebella that binds to single-stranded oligo-DNA of cAMP response element and is modulated by morphine treatment. Isolation of the cDNA clone showed that the nuclear protein (ssCRE-BP) was identical to Pur alpha, a DNA binding protein for single-stranded purine-rich sequences that was originally isolated as a replication factor. ssCRE-BP/Pur alpha and mRNA were abundant in the brain. The levels of ssCRE-BP/Pur alpha and the transcript were not changed by chronic morphine treatment, however, the levels of an activator of ssCRE-BP/Pur alpha, which is necessary for the DNA binding, may be modulated by the treatment.

Intracellular pH and intrinsic H+ buffering capacity in normal and hypertrophied right ventricle of ferret heart

OBJECTIVE

To answer the questions: (a) What is the effect of hypertrophy on the intracellular pH (pHi) and buffering power of cardiac muscle, and (b) How does hypertrophy affect the ability of cardiac muscle to recover from intracellular acidosis induced by hypoxia.

METHODS

In nominally HCO3(-)-free, HEPES-buffered Tyrode solution (35 degrees C), pHi and the intrinsic buffering power (beta i, measured in the presence of amiloride) was investigated using pH-sensitive microelectrodes.

RESULTS

beta i was similar in both preparations (25 mM/pH unit at pHi 7.04). beta i was inversely related to pHi but the relationship was not significantly modified by hypertrophy. In the absence of amiloride, the time constant of pHi recovery (tau r) on removal of NH+4, was similar in normal (4.0 +/- 0.2 min, n = 5) and in hypertrophied muscles (4.3 +/- 0.3 min, n = 4; n.s.). In both preparations, net acid extrusion (JH) was similarly increased at lower values of pHi. Lowering temperature from 35 degrees to 22 degrees caused an alkalinization (0.15 pH units) of pHi. At 22 degrees C the mean values of pHi, beta i, tau r and JH were similar in normal and in hypertrophied muscles. At both temperatures and in both groups of preparations, recovery of pHi following hypoxia is approximately exponential. The time constant of recovery of pHi following hypoxia (tau rh) at 22 degrees C was not significantly different in hypertrophied muscles (7.2 +/- 0.9 min, n = 8) compared to controls (10.6 +/- 1.8 min, n = 13). However, at 35 degrees C, there was a significant difference in the mean values of tau rh which was smaller for hypertrophied muscles (3.9 +/- 0.3 min, n = 7) than for normal (7.1 +/- 1.1 min, n = 4, P < 0.005). For pHi 6.8-7.0, net acid extrusion in hypertrophied preparations was increased by a factor of 4 compared to normal.

CONCLUSIONS

The intracellular buffering capacity and the pHi regulating capacity via Na+/H+ exchange are not significantly modified by right ventricular hypertrophy in ferret heart. The faster pHi recovery from hypoxia-induced acidification can be interpreted in terms of the role of lactate efflux in pHi control. The possible role of energy compartmentalization, its influence on the Na+ gradient and thus on pHi control after hypoxia, is discussed.

Alterations in the force-frequency relationship by tert-butylbenzohydroquinone, a putative SR Ca2+ pump inhibitor, in rabbit and rat ventricular muscle

1. The effects of 2,5 di-(tert-butyl)-1,4-benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, on twitch tension, time course and SR Ca2+ content have been studied at different stimulation frequencies (0.5-3 Hz) in isolated preparations from the rabbit and rat right ventricle, at 37 degrees C. 2. At 0.5Hz, 30 microM TBQ induced a marked negative inotropic effect in both species (-57% in the rabbit and -68% in the rat) and decreased the rate of rise and fall of twitch tension. In parallel, SR Ca2+ content (assessed by rapid cooling contractures) was depressed in the rabbit by 42%. The force-frequency relationship (positive for the rabbit and negative for the rat) was significantly attenuated. In the rabbit, this alteration was shown to rely on insufficient SR Ca2+ reloading with increasing frequencies. 3. Exposure of TBQ-treated preparations to 8 mM extracellular Ca2+ or 5 microM isoprenaline were effective in reloading the SR with Ca2+ whereas 20 mM caffeine emptied this compartment. 4. In the rabbit ventricle, increase in stimulation frequency shortened control twitch time course by decreasing both the time to peak tension (TTP) and the time to half relaxation (t1/2). TBQ did not differentially affect the pattern for t1/2 but significantly attenuated the frequency-induced decrease of TTP. 5. In rabbit ventricular muscle, the action potential duration increased between 0.5 and 3 Hz whether or not TBQ was present. However, TBQ induced a small but significant additional action potential shortening. 6. TBQ decreased twitch tension in the rat ventricle between 0.5 and 3 Hz but the negative staircase was not differentially affected by the SR Ca2+ pump inhibitor. In control conditions and in the presence of 30 microM TBQ, t1/2 was frequency-independent but TBQ consistently increased this parameter (by approximately 29%). 7. These data argue in favour of a specific and partial inhibition of the SR Ca2+ pump by 30 microM TBQ in the rabbit and rat ventricle and emphasise the importance of SR Ca2+ uptake in the force-frequency phenomenon.

The effects of compensated cardiac hypertrophy on dihydropyridine and ryanodine receptors in rat, ferret and guinea-pig hearts

The number of dihydropyridine and ryanodine receptors (DHP-R and RyR) has been measured in control and hypertrophied ventricles from rats, guinea pigs and ferrets to determine whether these two channels contribute to the alterations in excitation-contraction coupling (ECC), and in Ca2+ transient during compensated cardiac hypertrophy. We found that ventricular hypertrophy did not change the density of DHP-R. Mild hypertrophy did not alter the density of RyR in the rat but decreased it in the guinea-pig and in the ferret (30% and 36%, respectively). Severe hypertrophy decreased the density of RyR by 20% in the rat and by 34% in the guinea-pig. Therefore, the decrease is greater in ferret and guinea-pig hearts than in rat heart. We conclude that the sarcoplasmic reticulum (SR) Ca2+ release channels but not the L-type Ca2+ channels could contribute to the slowing of intracellular Ca2+ movements and to the reduced velocity of shortening of the hypertrophied hearts. We suggest that, in the guinea pig and ferret hearts which express only the beta myosin heavy chain (MHC) isoform, the reduced velocity of shortening during hypertrophy is related to the decrease in RyR density, whereas in the rat, it is regulated primarily via a shift in the MHC isoform, except in severe hypertrophy in which the moderate decrease in RyR would also be involved.

Intracellular pH during hypoxia in normal and hypertrophied right ventricle of ferret heart

The effects of preventing oxidative phosphorylation on pHi were compared in papillary muscles from right ventricles of normal and pressure-overloaded ferret hearts. Hypertrophy was induced by pulmonary artery clipping for 30-45 days. pHi was recorded with pH-sensitive microelectrodes. Resting pHi and the relationship between intracellular buffering power and pHi were not modified by the hypertrophy. At 22 degrees C, the initial intracellular alkalosis following exposure to oxygen-free Tyrode solution (containing the reducing agent sodium dithionite, 1 mM), as well as the transient acidosis on return to oxygenated solution, were reduced in hypertrophied papillary muscles. During hypoxia, exposure to alpha-cyano-4-hydroxycinnamate (5 mM) induced a larger intracellular acidification in hypertrophied than in control muscle. The initial alkalosis during hypoxia and the extra acidification on recovery from hypoxia were also significantly reduced in hypertrophied muscles at 35 degrees C. Moreover, the acidification during hypoxia was markedly accentuated in hypertrophied preparations at this temperature. [Mg2+]i and [Ca2+]i were also measured during metabolic inhibition, using mag-fura-2 and fura-2 respectively, in isolated cells from control and hypertrophied right ventricles. Hypertrophy increased the resting level of [Ca2+]i and of [Mg2+]i by a factor of 2.5 (P < 0.001) and 1.3 (P < 0.05) respectively. Upon application of 15 mM 2-deoxyglucose, [Mg2+]i was increased to a similar extent in control and hypertrophied cells. It is concluded that right ventricular hypertrophy could modify creatine phosphate metabolism and the capacity to recruit anaerobic glycolysis.

Pharmacological characterization of the quisqualate receptor coupled to phospholipase C (Qp) in striatal neurons

A detailed pharmacological characterization of the quisqualate (QA) receptor coupled to phospholipase C (Qp) was performed in striatal neurons. The experiments were carried out in the presence of the ionotropic antagonists MK-801 (1 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), concentrations that block N-methyl-D-aspartate (NMDA) or alpha-amino-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in these cells. QA, ibotenate and trans-1-aminocyclopentyl-1,3-dicarboxylate (ACPD) evoked dose-dependent inositol phosphate formations with EC50 values of 0.3, 6.7 and 29 microM, respectively. QA and ibotenate had the same maximal effect (295.7 +/- 17.9% of basal, n = 6) whereas the efficacy of ACPD was somewhat lower (70.2 +/- 8.9% of the maximal quisqualate effect, n = 4). The QA-, ibotenate- and ACPD-induced maximal effects were not additive, and the inositol phosphate formations induced by high concentrations of L-aspartate (L-ASP), AMPA, kainate (KA) and domoate (DO) (100 microM or higher) were also not additive. The inositol phosphate responses induced by all these agonists were totally blocked by the phorbol ester phorbol 12,13-dibutyrate (PdBu), but not by atropine or prazosin suggesting that all these substances were able to stimulate the Qp excitatory amino acid receptor in striatal neurons. Of the excitatory amino acid receptor antagonists tested, only D,L-2-amino-3-phosphonopropionate (D,L-AP3) inhibited QA-induced InsP formation in a competitive manner (mean pKi = 4.45 +/- 0.43, n = 4). However, this drug was also a partial agonist of the Qp receptor since it stimulated the inositol phosphate formation. We found that D,L-AP3 also inhibited NMDA-induced calcium increase, in a competitive manner (mean pIC50 = 4.34 +/- 0.22, n = 8, and mean pKi = 3.7 +/- 0.11, n = 5). The Qp excitatory amino acid receptor in striatal neurons therefore closely resembles Qp receptors with high potency for agonists as described in striatal and retinal slices and synaptoneurosomes, and has several pharmacological differences compared to the Qp receptors which have low potency for agonists described in hippocampal and cortical slices, cerebellar granule cells, astrocytes and rat brain mRNA-injected oocytes.