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Biomedical subjects

M Yamaki

Publications and source records attributed to M Yamaki.

At least 19 recordsLinked to original sources
PubMed2000

Diphenyleneiodonium prevents reactive oxygen species generation, tyrosine phosphorylation, and histamine release in RBL-2H3 mast cells.

Mast cells play a central role in immediate allergic reactions mediated by immunoglobulin E. It has recently been reported that mast cells generate intracellular reactive oxygen species (ROS) in response to stimulation with divergent physiologically relevant stimulants. However, the physiological role of ROS is poorly understood. Here we demonstrate that mast cell model rat basophilic leukemia (RBL-2H3) cells generate ROS in response to antigen and the calcium-ionophore A23187 via activation of diphenyleneiodonuim (DPI)-sensitive enzyme and that blockade of ROS generation by DPI suppresses histamine release induced by either stimulant. Increased tyrosine phosphorylation of pp125(FAK) and a 77-kDa protein coprecipitating specifically with the kinase occurred in parallel with the secretion, and blockade of ROS generation by DPI also suppressed the tyrosine phosphorylation of both proteins. These findings suggest that ROS generated by a flavoenzyme-dependent mechanism may be involved in histamine release through the pp125(FAK) pathway.

Animals↗
PubMed2000

Epigallocatechin gallate inhibits histamine release from rat basophilic leukemia (RBL-2H3) cells: role of tyrosine phosphorylation pathway.

Some tea polyphenolic compounds including (-)-epigallocatechin gallate (EGCG) have been shown to inhibit histamine release from mast cells through poorly understood mechanisms. By using a mast cell model rat basophilic leukemia (RBL-2H3) cells we explored the mechanism of the inhibition. EGCG inhibited histamine release from RBL-2H3 cells in response to antigen or the calcium-ionophore A23187, while (-)-epicatechin (EC) had little effect. Increased tyrosine phosphorylation of several proteins including approximately 120 kDa proteins occurred in parallel with the secretion induced by either stimulation. EGCG also inhibited tyrosine phosphorylation of the approximately 120-kDa proteins induced by either stimulation, whereas EC did not. The tyrosine kinase-specific inhibitor piceatannol inhibited the secretion and tyrosine phosphorylation of these proteins induced by either stimulation also. Further analysis showed that the focal adhesion kinase pp125(FAK) was one of the approximately 120-kDa proteins. These findings suggest that EGCG prevents histamine release from mast cells mainly by inhibiting tyrosine phosphorylation of proteins including pp125(FAK).

Animals↗
PubMed2000

Four putative subtypes of human parvovirus B19 based on amino acid polymorphism in the C-terminal region of non-structural protein.

The nucleotide sequence of 10 isolates of human parvovirus B19 (B19) were determined and compared throughout 96.3% of the open reading frames (4145 nucleotides from nt. 509-4653). In the 4145 nucleotides, 122 mutation sites were found, of which 24 were accompanied by amino acid displacement. Furthermore, the polymorphism of the amino acids was seen in about 110 bases near the carboxy terminal of the non-structural protein, ranging from nt. 2011 to 2123, where four amino acid mutation points were found to exist. Based on the amino acid polymorphism of these four mutation sites in this area, 10 isolates of the B19 parvovirus could be divided into 4 subtypes (subtypes A, B, C, and D). The frequency of isolation of the subtypes depended on the time and location of collection of the B19 viremic blood specimens.

Amino Acid Sequence↗
PubMed2000

Phenanthrenes from Dendrobium plicatile.

From Dendrobium plicatile stems, three phenanthrenes were isolated. The structures are 2,5-dihydroxy-4,9,10-trimethoxyphenanthrene, 2,5-dihydroxy-4-methoxyphenanthrene and 2,5,9-trihydroxy-4-methoxy-9,10-dihydrophenanthrene.

Magnetic Resonance Spectroscopy↗
PubMed2000

4-aminopyridine inhibits the occurrence of ventricular fibrillation but not ventricular tachycardia in the reperfused, P6olated rat heart.

The 4-aminopyridine (4-AP)-sensitive transient outward current (Ito) has been reported to play an important role in the ischemia- or high [Ca2+]o-induced reentrant ventricular arrhythmias. However, the role of 4-AP sensitive Ito in reperfusion arrhythmia remains unknown. Rat hearts were perfused with Tyrode solution (control), and treated with 0.5 micromol/L verapamil, 1 micromol/L glibenclamide, 10 micromol/L E-4031 or 2 mmol/L 4-AP. After a 10-min perfusion, hearts were subjected to 30-min global ischemia followed by 10-min reperfusion. The effects of the ion-channel blockers on the incidence of ventricular tachycardia (VT), torsades de pointes (Tdp) and ventricular fibrillation (VF) during the reperfusion period were investigated. Verapamil and 4-AP abolished VF and Tdp. The incidence of VT was also attenuated by verapamil, but not by 4-AP. Glibenclamide and E-4031 (a blocker of a rapidly activating component of delayed rectifier K+ current) did not affect the incidence of those tachyarrhythmias. Accordingly, (1) the underlying mechanism of VF or Tdp is different from that of VT, and (2) 4-AP sensitive Ito is required for the occurrence of reperfusion Tdp or VF in the present model.

4-Aminopyridine↗
PubMed2000

Anisotropic effects of sodium channel blockers on the wavelength for ventricular excitation in dogs.

The purpose of this study was to determine the anisotropic effects of sodium channel blockers on wavelength (WL) and proarrhythmia. In 18 anesthetized, open chest dogs, a 64-electrode array was placed on the left ventricle and the ventricle was constantly paced. Disopyramide, lidocaine or flecainide was intracoronarily administered. Conduction velocity (theta) and activation-recovery interval (ARI) were measured in the longitudinal (L) and transverse (T) directions. Flecainide markedly decreased thetaL, but did not alter thetaT or ARIs in either direction. As a result, the wavelength was significantly shortened only in the L direction. Disopyramide or lidocaine did not show direction-dependent effects on theta or WL. In 3 of 6 dogs with flecainide exposure, ventricular fibrillation (VF) developed. However, no VF occurred with disopyramide or lidocaine. Accordingly, the WL is dependent on the fiber orientation of myocardium. The anisotropic shortening of the WL may explain the character of the proarrhythmia observed with flecainide.

Action Potentials↗
PubMed2000

Dobutamine stress echocardiography for the diagnosis of myocardial viability: assessment of left ventricular systolic velocities in longitudinal axis by pulsed Doppler tissue imaging.

Dobutamine (DOB) stress two-dimensional echocardiography is an established method for the detection of viable myocardium, but conventional assessment of wall motion is subjective. We measured quantitatively the left ventricular systolic velocities along the longitudinal axis by pulsed Doppler tissue imaging (DTI). In 30 patients with previous myocardial infarction, pulsed DTI focused on the infarct area was performed from an apical two- or four-chamber view before and during DOB (10 microg/kg/min) stress one day before coronary angioplasty. We calculated peak systolic velocity (S), regional pre-ejection period (PEP, the time interval from the onset of QRS to the onset of systolic wave) and regional ejection time (ET). Left ventriculography was obtained before and 3 months after coronary angioplasty to assess regional wall motion. Improvement of abnormal wall motion was observed in 19 patients (group P) but not in 11 (group N). Group P had significantly larger S and smaller PEP/ET than group N during DOB stress, although there were no significant differences in these indices between the groups at baseline. As a consequence, group P had a significantly larger percent change in S and a smaller percent change in PEP/ET than group N (164+/-39 vs 117+/-20% and 88+/-17 vs 116+/-29%, respectively, p < 0.01). It is suggested that the quantitative measurement of longitudinal systolic velocities during DOB stress by DTI is useful for the precise assessment of myocardial viability.

Adult↗
PubMed2000

Simple microplate method for determination of urinary iodine.

BACKGROUND: Urinary iodine is a good biochemical marker for control of iodine deficiency disorders. Our aim was to develop and validate a simple, rapid, and quantitative method based on the Sandell-Kolthoff reaction, incorporating both the reaction and the digestion process into a microplate format. METHODS: Using a specially designed sealing cassette to prevent loss of vapor and cross-contamination among wells, ammonium persulfate digestion was performed in a microplate in an oven at 110 degrees C for 60 min. After the digestion mixture was transferred to a transparent microplate and the Sandell-Kolthoff reaction was performed at 25 degrees C for 30 min, urinary iodine was measured by a microplate reader at 405 nm. RESULTS: The mean recovery of iodine added to urine was 98% (range, 89-109%). The theoretical detection limit, defined as 2 SD from the zero calibrator, was 0.11 micromol/L (14 microg/L iodine). The mean intra- and interassay CVs for samples with iodine concentrations of 0.30-3.15 micromol/L were < or = 10%. The new method agreed well with the conventional chloric acid digestion method (n = 70; r = 0.991; y = 0.944x + 0.04; S(y|x) = 0.10) and with the inductively coupled plasma mass spectrometry method (n = 61; r = 0.979; y = 0.962x + 0.03; S(y|x) = 0.20). The agreement was confirmed by difference plots. The distributions of iodine concentrations for samples from endemic areas of iodine deficiency diseases showed similar patterns among the above three methods. CONCLUSIONS: Our new method, incorporating the whole process into a microplate format, is readily applicable and allows rapid monitoring of urinary iodine.

Adult↗
PubMed1999

Intracoronary flecainide induces ST alternans and reentrant arrhythmia on intact canine heart: A role of 4-aminopyridine-sensitive current.

BACKGROUND: The electrical alternans shown on an ST segment, ST alternans, is known as one of the most important predictors of ventricular fibrillation (VF). It has also been reported that sodium channel inhibition changes action potential configuration, especially on the repolarization phase. Thus, the sodium channel blocker may produce ST alternans and trigger reentrant arrhythmia. METHODS AND RESULTS: A sodium channel blocker (disopyramide, lidocaine, or flecainide) was infused selectively into the left anterior descending coronary artery in anesthetized, open-chest dogs. Sixty unipolar electrograms were simultaneously recorded from the entire cardiac surface of the heart. The amplitude of ST alternans (STa) was determined as the difference in the ST-segment magnitude between 2 consecutive electrograms. We accepted the greatest STa among 60 leads for evaluation. High-dose flecainide (100 microg. kg-1. min-1) increased STa and evoked a spontaneous VF. The STa in high-dose flecainide loading (8.7+/-3.4 mV; mean+/-SEM) was significantly greater than that in disopyramide or lidocaine (0. 9+/-0.4 and 0.8+/-0.2 mV, P<0.05). Treatment of 4-aminopyridine (4-AP) suppressed the increase in STa and the occurrence of VF evoked by flecainide, while E4031 or verapamil did not inhibit those. CONCLUSIONS: Flecainide caused the ST alternans that was closely correlated to the occurrence of VF. Because the ST alternans was suppressed by 4-AP treatment, a 4-AP-sensitive current such as Ito or Isus may play an important role on this phenomenon.

4-Aminopyridine↗
PubMed1999

A multiparametric analysis of occlusal and periodontal jaw reflex characteristics in adult skeletal mandibular protrusion before and after orthognathic surgery.

Periodontal jaw reflex, duration of percussion sounds, tooth mobility, and time-moment analysis of occlusal contacts by the T-scan system were recorded in seven pre-orthognathic surgery patients and six post-orthognathic surgery patients over a 2-year period. The results showed that: (i) reflex response to the pressure applied to the upper right central incisor in the lingolabial direction varied, depending on the background jaw-clenching force (BCF) of the same-sided first molar. The BCF level required to elicit excitatory reflexes was only 0 kgf, and inhibitory reflexes were clearly elicited with a BCF of 1 kgf and beyond before orthognathic surgery. After orthognathic surgery BCF levels required to elicit excitatory reflexes were 0-4 kgf, and inhibitory reflexes were elicited with a BCF of 6 kgf and above; (ii) duration of percussion sounds determined via an occlusal sound analyser decreased in both the upper right central incisor and upper right first molar while tooth mobility measured by 'Periotest(R)' increased in the upper right central incisor, but did not change in the same-sided first molar after orthognathic surgery; (iii) the time moments of occlusal contacts were symmetrical toward the midsagittal axis of the occlusal plane after orthognathic surgery. The centre of the anterioposterior occlusal contacts did not differ between pre- and post-orthognathic surgery groups.

Adolescent↗
PubMed1999

Relation between activation sequence fluctuation and arrhythmogenicity in sodium-channel blockades.

To examine the correlation between activation sequence fluctuation and arrhythmogenicity, we investigated temporal changes in the activation sequence by measuring activation times [negative first derivative of voltage over time (-dV/dt) in QRS] from the entire heart in 18 dogs. The heart was paced by constant atrial stimulation. The character of the activation sequence fluctuation was established by a principal component analysis, in which the first principal component was defined as a stable component of the sequence and the second or third component as a fluctuated component. Steady state contained 2.2 +/- 0.6% (percent total principal component, mean +/- SD) of fluctuated components, which appeared in a beat-by-beat manner (activation sequence alternans). Activation sequence alternans was observed only during flecainide administration and not during lidocaine or disopyramide administration. Fluctuated components at a high dose of flecainide significantly increased (3.3 +/- 0.8%). Ventricular fibrillation ensued in all dogs (n = 6) exposed to flecainide after an increase in activation sequence alternans. In conclusion, flecainide evoked local activation sequence alternans. This phenomenon correlated with the occurrence of ventricular fibrillation.

Animals↗
PubMed1999

Canine model of ventricular fibrillation using programmed stimuli and localized myocardial warming or cooling.

The purpose of this study was to establish an animal model in which ventricular fibrillation (VF) can be induced reproducibly and defibrillation can be accomplished repeatedly. The left anterior descending artery (LAD) was cannulated and perfused with blood from the carotid artery in eleven open-chest dogs. Electrodes of the internal defibrillator were inserted in the cavities of the left atrium and left ventricle via incisions in the left atrial appendage and left ventricular apex. The perfused blood temperature was modulated to produce regional myocardial warming (42 degrees C) or cooling (28 degrees C). In all dogs, VF was repeatedly induced by the combination of warming and left ventricular extrastimuli and by the combination of cooling and right ventricular extrastimuli. The VF was quickly defibrillated by use of the internal defibrillator. The mechanism of VF was found to be reentry by the analysis of activation sequences. This VF model may be useful when evaluating the efficacy of antiarrhythmic drugs because of the high reproducibility.

Animals↗
PubMed1999

Direct effects of class I antiarrhythmic drugs on epicardial electrograms in dogs.

The effects of class I antiarrhythmic drugs on epicardial electrograms during regular atrial pacing were investigated in anesthetized, open-chest dogs. Lidocaine, flecainide or disopyramide was infused selectively into the distal site of the left-anterior descending artery. Lidocaine produced a dose-dependent elevation of ST segment without changing the amplitude of R wave. Flecainide produced a dose-dependent increase of R-wave amplitude accompanied by the augmentation of negative T. The ST segment was elevated at the high dose. The QRST area did not change at the low dose but significantly increased at the high dose, indicating that the ST-T change at the low dose was secondary to changes in ventricular depolarization. The effects of disopyramide on R wave and ST segment were between those of lidocaine and flecainide. The major action of lidocaine was the acceleration of ventricular repolarization while that of flecainide was the deceleration of ventricular conduction. Disopyramide had an action that was intermediate between the two drugs.

Animals↗
PubMed1999

Simulation of late potentials and arrhythmias by use of a three-dimensional heart model: casuality of peri-infarctional slow conduction in ventricular fibrillation.

A three-dimensional heart model was constructed to simulate late potentials and ventricular fibrillation (VF). The model consisted of 50,000 discrete elements having a 1.5-mm spatial resolution. Each element represented excitable ventricular tissue, including a conduction system, and was characterized with classical features of the action potential, refractory period, and conduction velocity (theta). An infarcted area on the lateral wall was identified as dead (inexcitable) cells or scar tissue, and peri-infarctional (PI) cells with slow conduction. Body surface potentials were calculated by using the boundary element method. When theta of PI cells was reduced below 0.3 m/s, late potentials became evident after the J point of simulated electrocardiograms (ECGs), and VF was induced by applying four consecutive premature stimuli. However, when Purkinje fibers were removed, VF could not be initiated. Late potentials were induced when slow conduction was present. The presence of PI slow conduction and Purkinje fibers, which were normally contained in the model, was essential for the induction of VF.

Computer Simulation↗
PubMed1998

Hexagonal bilayer structuring activity of linker chains of an annelid giant hemoglobin from the polychaete Perinereis aibuhitensis.

Preferential activity of linker chains to clamp submultiples to form hexagonal bilayer (HBL) assembly of the multisubunit hemoglobin (Hb) of the polychaete Perinereis aibuhitensis (approximately 3.4 MDa) was demonstrated. To understand the HBL assembly that should rely on structuring activity of each subunit, reassociation in response to combining isolated subunits was monitored using gel filtration, SDS-PAGE, and transmission electron microscopy. The isolation of each subunit L, T, and M (L, linker chains; T, disulfide-bonded trimer A-b-B; M, monomeric chain a) of Perinereis Hb was made simply by exposing Hb to pH 10.5, where Hb was completely dissociated into its subunits L, T, and M. As a result, it was concluded that (i) subunits T and M have strong affinity to form an intermediate complex, submultiple D, which is a dodecamer of globin chains, 3[a. A-b-B], (ii) addition of subunit L to submultiple D brings about the formation of whole molecule, similarly (iii) addition of subunit M to T+L forms the whole molecule, and (iv) addition of subunit T to M+L brings about the formation of the whole molecule, too. The results obtained lead us to conclude that linkers do function to clamp 12 submultiples D up to a whole molecule at the final step of formation of Perinereis Hb. In summary, linkers appeared to have high affinity for submultiple D, a little affinity for subunit T, but no affinity for subunit M at all. Thus linker chains were demonstrated to preferentially clamp submultiples D together to form the HBL disc of the whole molecule.

Animals↗
PubMed1998

A novel variant of translation elongation factor-1beta: isolation and characterization of the rice gene encoding EF-1beta2.

A rice gene encoding a novel isoform of translation elongation factor-1beta subunit (termed EF-1beta2) was isolated and characterized. The gene comprises of eight exons, and encodes a 226-amino-acid protein. Expression of EF-1beta2 mRNA is abundant in seeds and cultured cells, but is considerably low in the tissues of the rice seedling. Antiserum raised against an EF-1beta2 synthetic peptide detected a protein with a relative molecular mass of about 32 kDa, indicating the EF-1beta2 gene is actually expressed in rice tissues. EF-1beta2 showed a close similarity to the cognate subunits from plant (beta and beta').

Amino Acid Sequence↗
PubMed1998

Carbohydrate gluing is a strategy for supramolecular clamping of submultiples in annelid extracellular multi-subunit hemoglobin.

A key to understanding the mysterious hierarchic organization of annelid multi-subunit extracellular hemoglobin (giant Hb, composed of 144 globin chains and about 36 nonheme chains called linkers) is knowing the role of linkers in holding together the entire two-tiered hexagonal form. Here, the effects of added monosaccharides on the dissociation of giant Hb from the marineworm Perinereis aibuhitensis were monitored using dynamic light scattering (DLS), transmission electron microscopy (TEM), and circular dichroism (CD) measurements. Changes in Stokes radius and more clearly the distribution analysis of the Hb based on the DLS measurements showed that Hb preferentially dissociates into hexagonal units (called submultiples), which was consistent with the results of TEM and CD measurements. The results thus show that linkers specifically "clamp" submultiples together to organize the two-tiered form through carbohydrate gluing. Thus, a submultiple behaves like an ordinary protein, whereas the intact Hb behaves like a miniature supramolecular system. This clamp model is plausible because it inherently involves catastrophe of the molecular stoichiometry at the two-tiered hexagonal formation level because carbohydrates are under posttranslational regulation and therefore contain structural ambiguity.

Animals↗