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Biomedical subjects

H Miyoshi

Publications and source records attributed to H Miyoshi.

At least 199 records · Page 11Linked to original sources
PubMed1994

Comparison of the inhibitory action of natural rotenone and its stereoisomers with various NADH-ubiquinone reductases.

Two stereoisomers of natural rotenone (5'alpha-epirotenone and 5'beta-epirotenone) were synthesized to identify the stereochemical factor of rotenone required for the inhibition and also to probe the structure of the rotenone binding site. The inhibitory action of the stereoisomers was compared with that of rotenone using NADH-ubiquinone reductases from bovine heart submitochondrial particles (SMP), potato tubers (Solanum tuberosum L.) SMP and Escherichia coli (GR19N) membranes. With respect to bovine heart SMP, it was found that the bent form of rotenone is essential for the activity. The modification of the E-ring moiety also affected both the inhibitory potency and the pattern of inhibition. These results indicated that the rotenone-binding site recognizes the whole molecular structure (or shape) of rotenone in a strict sense. Rotenone and 5'beta-epirotenone inhibited the NADH-ubiquinone reductase of bovine heart SMP in a noncompetitive manner against exogenous quinones. In contrast, the inhibition pattern of 5'alpha-epirotenone varied from noncompetitive to competitive as the concentration of quinone increased. These results suggest that rotenone binds close to, but not at a site identical to, the location for ubiquinone in the ubiquinone-catalytic reaction site, whereas the 5'alpha-epirotenone-binding site overlaps that for ubiquinone due to a structural modification of E-ring moiety. Furthermore, the complex inhibition pattern of 5'alpha-epirotenone suggests that there are two quinone-binding sites in NADH-ubiquinone reductase. In contrast, the order of the inhibitory potencies of the three inhibitors with proton-pumping NADH-ubiquinone reductase of potato SMP was the same as that observed for the bovine enzyme. This suggests that the structure of rotenone-binding sites (or ubiquinone-binding sites) of these enzymes are similar. It was further demonstrated that 5'alpha-epirotenone inhibits quinone binding to both proton-pumping and non-proton-pumping NADH-ubiquinone reductases of potato SMP in a competitive manner. With respect to the proton-pumping NADH-ubiquinone reductase of the E. coli membrane, the sensitivity of the enzyme to the inhibitor was remarkably decreased and the difference in the inhibitory potencies of the three inhibitors became ambiguous. In addition, the inhibition pattern of the three inhibitors was competitive against quinone. These results indicated that, contrary to the mammalian enzyme, only part of the rotenone molecule is recognized by the quinone-binding site of this enzyme.

Animals↗
PubMed1994

Nonendothelial-derived nitric oxide activates the ATP-sensitive K+ channel of vascular smooth muscle cells.

To determine whether endogenous nitric oxide (NO) opens the ATP-sensitive K+ channel (KATP channel), we investigated the effect of nonendothelial-derived NO on this channel in cultured smooth muscle cells of the porcine coronary artery by the patch-clamp technique. In the cells pretreated with endotoxin, the addition of 10(-4) M L-arginine generated NO and activated the KATP channel. Activation of this channel was suppressed by pretreatment with 10(-3) M NG-methyl-L-arginine or 10(-3) M Nx-nitro-L-arginine methyl ester, each of which is a specific antagonist of the L-arginine-NO pathway, and by 10(-6) M Methylene blue, which blocks guanylate cyclase. The activation of the KATP channel by L-arginine-NO pathway is expected to produce hyperpolarization of the cell membrane and relaxation of vascular smooth muscle cells.

Adenosine Triphosphate↗
PubMed1994

Structural factors of antimycin A molecule required for inhibitory action.

A series of antimycin A analogues was synthesized by modifying the salicylic acid moiety, whereas the portion of the molecule corresponding to the natural dilactone-ring moiety was fixed as di-n-octyl L-glutamate. To probe the structure of the antimycin A binding site, the structural factors of the salicylic acid moiety required for inhibitory action were examined by means of structure-activity studies with intact rat-liver mitochondria and the cytochrome bc1 complex isolated from bovine heart mitochondria. As suggested earlier (Rieske, J.S. (1976) Biochim. Biophys. Acta 456, 195-247), the phenolic OH was very important for inhibition. For the derivatives which do not possess a formylamino group in the 3-position (ortho to the phenolic OH), the inhibitory activity tended to increase as the electron-withdrawing property of the substituent increased, i.e., as the acidity of the phenolic OH group increased. This indicates that the acidity of the phenolic OH is an important factor governing inhibition. While the electron-withdrawing property of the formylamino group itself is rather poor, 3-formylamino derivatives elicited potent activity. The conformation of the 3-formylamino group was also found to be a very important factor in establishing inhibitory activity. In addition, the bulkier the moiety corresponding to the 3-formylamino group, the lower the activity. These results demonstrate that the presence of the 3-formylamino group, and its proper conformation, are needed for a close fitting of antimycin A to its binding domain. Although the inhibitors that lack a 3-formylamino group retained fairly potent activity, their effects on the reduction of cytochromes b and c1 were somewhat different from those of natural antimycin A, indicating that the 3-formylamino group is essential for inhibitor binding to the cytochrome bc1 complex in the same manner as natural antimycin A. It is concluded that both the 3-formylamino group and the phenolic OH of antimycin A make important contributions to specific interactions with the amino acid residues of the cytochrome b.

Animals↗
PubMed1994

Analysis of revertants from respiratory deficient mutants within the center N of cytochrome b in Saccharomyces cerevisiae.

Four modified cytochrome b's carrying mononucleotide substitutions affecting center N residues were analysed. The mutant carrying a G33D change does not incorporate heme into the apocytochrome b and fails to grow on non-fermentable carbon sources. Out of 85 genetically independent revertants derived from this mutant, 82 were true back-mutants restoring the wild type sequence (D33G). The remaining three replaced the aspartic acid by an alanine (D33A) indicating that small size residues are best tolerated at this position which is consistent with the perfect conservation of the G33 during evolution. This glycine may be of crucial importance for helix packing around the hemes. The replacement of methionine at position 221 by lysine (M221K) produced a non-functional cytochrome b [(1993) J. Biol. Chem. 268, 15626-15632]. Non-native revertants replacing the lysine 221 by glutamic acid (K221E) or glutamine (K221Q) expressed a selective resistance to antimycin and antimycin derivatives having a modified dilactone ring moiety. Cytochrome b residues in 33 and in 221 seemed to contribute to the quinone reduction (QN) site of the cytochrome bc1 complex. Possible intramolecular interactions between the N-terminal region and the loop connecting helices IV and V of cytochrome b are proposed.

Antimycin A↗
PubMed1994

Generation of the AML1-EVI-1 fusion gene in the t(3;21)(q26;q22) causes blastic crisis in chronic myelocytic leukemia.

The t(3;21)(q26;q22) translocation, which is one of the consistent chromosomal abnormalities found in blastic crisis of chronic myelocytic leukemia (CML), is thought to play an important role in the leukemic progression of CML to an acute blastic crisis phase. The AML1 gene, which is located at the translocation breakpoint of the t(8;21)(q22;q22) translocation found in acute myelocytic leukemia, was also rearranged by the t(3;21)(q26;q22) translocation. Screening of a cDNA library of the t(3;21)-carrying leukemic cell line cells (SKH1) resulted in the isolation of two potentially complete AML1-EVI-1 chimeric cDNAs of 6 kb. Two species of AML1-EVI-1 fusion transcripts of 8.2 and 7.0 kb were detected in SKH1 cells. These cells expressed the 180 kDa AML1-EVI-1 fusion protein containing an N-terminal half of AML1 including a runt homology domain which is fused to the entire zinc finger EVI-1 protein. The AML1-EVI-1 fusion transcript was consistent in all three cases of the t(3;21)-carrying leukemia examined by RNA-based PCR. These findings strongly suggest that the t(3;21) translocation results in the formation of a new class of chimeric transcription factor which could contribute to the leukemic progression of CML through interference with cell growth and differentiation.

3T3 Cells↗
PubMed1994

Noninvasive localization of accessory pathways by magnetocardiographic imaging.

The magnetocardiogram (MCG) is a newly developed method that helps localize a cardiac current source. To test the clinical accuracy of a 7-channel biomagnetic system in the localization of early ventricular depolarization sites, the MCGs of 14 patients with Wolff-Parkinson-White (WPW) syndrome were recorded in a radiofrequency-shielded room. The locations of early ventricular depolarization sites were classified by standard 12-lead electrocardiograms (ECGs) and body surface isopotential mapping. The accessory pathways of 3 patients with WPW syndrome were located in the right free wall and in 11 patients in the left free wall. The three-dimensional (3-D) dipole location was computed every 2 ms from the onset of the QRS complex by the least-square method. These 3-D dipole locations were projected onto a gated magnetic resonance image in order to visualize the propagation of the calculated ventricular source. The results were compared with those obtained by body surface isopotential mapping, and electrocardiographic and electrophysiologic studies. The location of the deduced current dipole at 20 ms correlated well with the location of the accessory pathway by the body surface mappings in 12 of the 14 patients with WPW syndrome. The MCG is capable of precisely determining the 3-D location of a current source in a noninvasive manner and may be of potential benefit in the treatment of WPW syndrome by catheter ablation.

Adolescent↗
PubMed1994

Endotoxin-induced nonendothelial nitric oxide activates the Ca(2+)-activated K+ channel in cultured vascular smooth muscle cells.

Endotoxin induces an enzyme that synthesizes nitric oxide (NO) from L-arginine (NO synthase) in vascular smooth muscle cells, resulting in nonendothelial NO release. In this study, we measured the NO release and its intracellular action on the Ca(2+)-activated K+ channel (KCa channel) in cultured smooth muscle cells of porcine coronary artery using a newly-developed porphyrinic-based microsensor and the patch-clamp technique. In smooth muscle cells pretreated with endotoxin, extracellular application of 10(-4) M L-arginine increased NO release, which induced rapid and prolonged activation of the KCa channel. This activation was only partially blocked by application of 10(-5) M 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-oxyl 3-oxide, which neutralizes NO. NO formation and activation of the KCa channel were suppressed by pretreatment with 10(-3) M NG-methyl-L-arginine or 10(-3) M N omega-nitro-L-arginine methyl ester, each of which is a specific antagonist of the L-arginine-NO pathway. One micromolar methylene blue, a blocker of guanylate cyclase, inhibited L-arginine-induced activation of the KCa channel. The effect of nitroprusside in opening the KCa channel was transient, although it induced production of larger amounts of NO in the bath. These results suggest that the endotoxin-induced and L-arginine pathway generates NO and directly modulates the KCa channel intracellularly in an autocrine manner.

Amino Acid Oxidoreductases↗
PubMed1994

Brain abscess observed by localized proton magnetic resonance spectroscopy.

We encountered a case of brain abscess that was difficult to differentiate from glioblastoma. Localized 1H-MRS was found to be useful for obtaining information on the biochemical status of brain abscess. The peak of lipid and high residual peak of NAA (N-acetyl-aspartate) were observed in the cystic lesion of the brain abscess by 1H-MRS. The NAA/Cho (Choline-containing compounds) ratio in brain parenchyma showing an edematous lesion before therapy gradually increased with the relief of inflammation.

Aspartic Acid↗
PubMed1994

Ultrasonographic diagnosis of juvenile colonic polyps.

To reduce the risks of air-contrast barium enemas and colonoscopy, we studied the use of saline enemas for ultrasonographic examination of children with rectal bleeding. Thirty-nine children, from 2 years 8 months to 8 years 3 months of age, were examined. Juvenile colonic polyps were ultrasonographically demonstrated and histologically confirmed in 25 children; all the polyps were solitary and pedunculated, and were located in the splenic flexure in 3 children, the descending colon in 6, the sigmoid colon in 12, and the rectum in 4. Ultrasonographic findings by hydrocolonic ultrasonography were identical to those obtained by immersion ultrasonography of removed specimens. Hypoechoic areas within more hyperechoic polyps were shown histologically to be dilated glandular canals. The 14 children in whom no abnormal ultrasonographic findings were shown had no further rectal bleeding after resuming regular defecation, and 5 of these 14 had negative colonoscopic findings. No adverse reactions were noted in any child during or after the saline enema examination. We conclude that ultrasonographic examination with a saline enema is a safe and accurate method of assessing children with rectal bleeding, especially for the diagnosis of juvenile colonic polyps.

Child↗
PubMed1994

Intracellular signal transduction systems do not regulate Na channel in frog ventricular cells.

The regulation of sodium channel activity through intracellular signal transduction systems was studied on isolated frog ventricular cells using a whole cell patch-clamp technique. Special care was exercised in evaluating the stability of the voltage-clamp condition by observing shifts in the steady-state inactivation curve (h infinity curve) and changes in series resistance. We applied the following reagents: isoproterenol (Iso; 0.1-10 microM) and forskolin (Fsk; 0.1-10 microM) to activate protein kinase A. 1-Oleoyl-2-acetyl-sn-glycerol (40 microM) and 12-O-tetradecanoylphorbol-13-acetate (80-800 nM) were used to activate protein kinase C, and phenylephrine (0.1-10 microM), dopamine (0.1-10 microM), and histamine (10 microM) were used to stimulate alpha-adrenergic, dopaminergic, and histaminergic receptors, respectively. The current-voltage relationship and the h infinity curve for the sodium channel remained unchanged regardless of the application of these reagents. Iso and Fsk did not affect the sodium current but substantially increased the calcium current, suggesting that the intracellular signal transduction systems remained intact. Therefore, it is concluded that sodium channel in frog ventricular cells is not regulated by intracellular signal transduction systems.

Animals↗
PubMed1994

Hemopneumothorax secondary to multiple cavitary metastasis in angiosarcoma of the scalp.

We report a case of hemopneumothorax secondary to multiple cavitary metastasis in the angiosarcoma of the scalp in an 86-year-old woman, who died of respiratory failure. At autopsy, multiple cavities were found in both lungs. Histologic specimen of the cavitary metastasis of the lung showed that tumor cells proliferated forming several tubular spaces and these tubular spaces seemed to communicate with the central cyst. These findings suggested that imperfect vessel-like structures of the cavitary metastasis are likely to break down and finally grow up to large thin-walled cavities.

Aged↗
PubMed1994

Time- and frequency-domain analyses of signal-averaged electrocardiograms in patients with diabetes mellitus.

We recorded the signal-averaged electrocardiography (SAECG) of patients with diabetic retinopathy in order to clarify whether a ventricular conduction disturbance can be detected by time- or frequency-domain analysis of the SAECG. Twenty-four normal subjects (N group) and 20 patients with diabetic retinopathy [diabetes mellitus (DM) group] were studied. On time-domain analysis, the duration of the filtered QRS (f-QRS), the duration of the terminal QRS below 40 microV (LAS40) and the root-mean-square amplitude of the terminal 40 msec (RMS40) were measured. The frequency-domain analysis was performed using two windows. In each window, the ratio of the area under the spectral curve from 40 to 100 Hz was compared with that from 0 to 40 Hz and the area from 20 to 50 Hz was compared with that from 0 to 20 Hz. The LAS40 of the DM group was significantly prolonged when compared with the N group. The area ratio from 40 to 100 Hz versus 0 to 40 Hz significantly increased in the DM group when compared with the N group. These results suggest that SAECG can be used to detect abnormal electrical signals due to diabetic microangiopathy. Moreover, high frequency components of 40 to 100 Hz at the terminus of the QRS wave were most sensitive for abnormalities due to diabetic microangiopathy.

Aged↗
PubMed1994

Cytoprotective effect of prostaglandin I2 analogues on superoxide-induced hepatocyte injury.

BACKGROUND: Prostaglandin I2 (PGI2) analogues have been suggested to protect the liver from ischemia-reperfusion injury, but the exact mechanism remains to be proved. METHODS: Primary cultured rat hepatocytes were exposed to superoxide generated by mixing hypoxanthine and xanthine oxidase, and changes in cell viability, cytosolic free calcium concentration ([Ca2+]i), and adenosine 3',5'-cyclic monophosphate (cAMP) concentration were assessed. The PGI2 analogue (OP2507 or OP41483) at 1 to 100 ng/ml was given as treatment. RESULTS: PGI2 analogues suppressed hepatocyte death in a dose-dependent manner (p < 0.01; OP2507 at 10 and 100 ng/ml, OP41483 at 100 ng/ml). At the end of 1-hour preincubation with OP2507, a significant rise in cAMP concentration was observed. Moreover, addition of dibutyryl cAMP suppressed hepatocyte death. A rise in [Ca2+]i, which preceded cell death, was prevented by PGI2 analogues or dibutyryl cAMP. CONCLUSIONS: The increase in cellular cAMP followed by suppression of [Ca2+]i elevation might be the major cause of the cytoprotective effect of PGI2 analogues in superoxide-induced hepatocyte injury.

Animals↗
PubMed1994

[Developmental changes in proton MR spectroscopy of the brain].

Volume-selective proton MR spectroscopy (1H-MRS) of the brain was performed on a 1.5 T magnet in 31 healthy children aged from 1 month to 15 years and one healthy adult. Peaks of N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) were observed in all cases on 1H-MRS, but not lactate. On 1H-MRS of the right parietal region, with advancing age, 1H-MRS revealed an increase in the ratios of NAA to Cho and NAA to Cr and a decrease in Cho to Cr. The most rapid change was noted during the first one to three years of life. 1H-MRS of the right frontal region was also performed in eleven cases. The ratio of NAA/Cho was smaller in the right frontal region than in the right parietal region. From this result, it may be suggested that the neuronal maturation in the frontal region delays as compared with the parietal region.

Adolescent↗
PubMed1994

[A case of Borrmann type 4 gastric cancer responding to sequential methotrexate and 5-fluorouracil combined with CDDP].

A case of Borrmann type 4 gastric cancer responding to sequential methotrexate and 5-fluorouracil combined with cis-diamminedichloroplatinum (CDDP) is reported. A 57-year-old woman was admitted to our hospital complaining of abdominal fullness. Upper gastrointestinal series and gastrofiberscopy revealed almost the entire stomach was involved with Borrmann type 4 cancer. Gastrectomy could not be performed because of peritoneal dissemination. However, the patient responded to sequential methotrexate and 5-fluorouracil therapy and CDDP administration. She enjoyed more than one year of hospital-free survival period and survived for almost two years.

Adenocarcinoma↗
PubMed1993

Comparison of the structures of the quinone-binding sites in beef heart mitochondria.

The ubiquinone pool in mitochondrial membranes serves as an electron carrier between both NADH-coenzyme Q oxidoreductase (Complex I) and succinate-coenzyme Q oxidoreductase (Complex II) and ubiquinol-cytochrome-c oxidoreductase (Complex III). It has been reported (Saitoh, I., Miyoshi, H., Shimizu, R., and Iwamura, H. (1992) Eur. J. Biochem. 209, 73-79) that 2-alkyl-4,6-dinitrophenols compete with exogenous coenzyme Q (Q) to inhibit electron transport through cytochromes b and c1 in mammalian mitochondria as well as in photosystem II. We have probed the similarities and differences in the reaction sites of exogenous Q in all three segments of the respiratory chain using selected 2-alkyl-4,6-dinitrophenols. The inhibition of Q analog reduction by the dinitrophenol derivatives was competitive for Complex I and noncompetitive for Complex II. The inhibition of Complex III was competitive with the pentyl analog, but was uncompetitive with the decyl analog, which may be due to different interactions of the two quinol analogs with Complex III. The degree of inhibition by several of these compounds was comparable for Complexes I and III, but Complex II was inhibited to a much smaller extent. The inhibitory potency of these compounds for Complexes I and III was increased by branching and by lengthening the carbon chain at the 2-position equivalent to the isoprenoid side chain of ubiquinone. Hydrophobic substituents increased the inhibition of Complex II. Replacement of the phenolic OH group by a chlorine atom decreased the maximum inhibition of Complex III, but increased that of Complex I. These data suggest that the structures of the exogenous Q-binding sites in Complexes I and III may be similar, but not identical, and that they are different from that in Complex II.

2,4-Dinitrophenol↗