Search PubMed⌕ Search

Biomedical subjects

T Ohta

Publications and source records attributed to T Ohta.

At least 721 records · Page 40Linked to original sources
PubMed1994

T and R states in the crystals of bacterial L-lactate dehydrogenase reveal the mechanism for allosteric control.

The crystal structure of L-lactate dehydrogenase from Bifidobacterium longum, determined to 2.5 A resolution, contains a regular 1:1 complex of T- and R-state tetramers. A comparison of these two structures within the same crystal lattice and kinetical characterization of the T-R transition in solution provide an explanation for the molecular mechanism of allosteric activation. Substrate affinity is controlled by helix sliding between subunits which is triggered by the binding of the activator, fructose 1,6-bisphosphate. The proposed mechanism can explain activation by chemical modification and mutagenesis, as well as suggesting why vertebrate counterparts are not allosteric.

Allosteric Regulation↗
PubMed1994

Simulation study on therapeutic vertebral artery occlusion for VA-PICA giant aneurysm.

We investigated haemodynamic effects of therapeutic vertebral artery (VA) occlusion on giant aneurysms at the bifurcation of the VA-posterior inferior cerebellar artery (PICA). An hydraulic model of the human vertebro-basilar artery was manufactured from glass and silicone tubes. Glass-spheres 2.5 cm in diameter were placed at the bifurcation as model aneurysms with respective distances of 8.5, 7.5, 6.5 and 5.5 mm between the VA union and aneurysmal neck. A 40% glycerol solution was perfused in this system and the half-life of the dye injected into aneurysms was regarded as an index of intra-aneurysmal stagnation. Flow conditions in aneurysms depended on the presence or absence of the effect of contralateral VA flow as well as the PICA flow. The half-life increased significantly after VA occlusion proximal to the PICA when the aneurysmal neck was more than 7.5 mm away from the VA union and PICA flow volume was less than 12 ml min-1. The half-life in aneurysms located within 6.5 mm from the union changed little after VA occlusion regardless of the PICA flow volumes. The haemodynamic simulation study would be helpful in speculating on the efficacy of this treatment.

Cerebellum↗
PubMed1994

Pressure gradients between intraluminal and extraluminal spaces may affect the potassium induced contraction in the rabbit's basilar arteries.

In order to investigate the different contactile effects between intraluminal and extraluminal vasoactive agents, we studied the contractile responses of rabbit basilar artery to selective intraluminal and extraluminal administration of potassium, serotonin and histamine in vitro. We also studied how the physical pressure gradients, such as hydrostatic or osmotic pressure gradients between intraluminal and extraluminal spaces, affect potassium-induced contraction. Intraluminal potassium (30 mM) induced a significantly greater contraction than extraluminal potassium. Serotonin (2 x 10(-7) M) and histamine (10(-5) M) applied intraluminally caused the same magnitude of the contraction as those applied extraluminally and no significant differences were noted between these applications. These differences in potassium-induced contraction were more significant when the intraluminal hydrostatic pressure was elevated by 20 mmHg. Contraction by either intraluminal or extraluminal potassium was significantly decreased when intraluminal pressure was raised by 40 mmHg. As the osmotic pressure gradients between the extraluminal and the intraluminal spaces were increased, these differences in potassium-induced contraction were decreased. Our findings suggest that physical pressure gradients may affect potassium-induced contraction in a different manner from pharmacologically-induced contraction and that free ions can penetrate the vascular wall by physical pressure gradients between the intraluminal and extraluminal spaces of cerebral artery.

Animals↗
PubMed1994

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) induces gene mutations and inhibits metabolic cooperation in cultured Chinese hamster cells.

Investigations were carried out on 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a potent direct-acting bacterial mutagen found in chlorinated tap water, for the potential to induce 6-thioguanine (6-TG) resistant mutations in cultured Chinese hamster V79 cells. The mutagenicity of MX was manifested when cells were treated with MX in Hanks balanced salt solution, but not in serum-free Eagle's minimal essential medium. A 12-fold higher mutation frequency over control was obtained at 12.5 micrograms/ml MX. In addition, the inhibitory effect of MX on metabolic cooperation between cocultivated 6-TG- sensitive (6-TGs) and -resistant (6-TGr) V79 cells was investigated. Recovery of 6-TGr cells significantly increased at 0.8-2.0 micrograms/ml MX due to impaired intercellular communication with 6-TGs cells. MX is believed to exert tumor-promoting and mutagenic activity in mammalian cells.

Animals↗
PubMed1994

Analbuminemia does not significantly influence hepatocarcinogenesis on comparing F344 rats and a congenic line carrying the analbuminemic mutation.

Analbuminemic rats differ from Sprague-Dawley rats (SD), their strain of origin, with respect to carcinogenic susceptibility of various organs. We compared hepatic changes after carcinogenic treatments in two kinds of analbuminemic rats with different genetic backgrounds (NAR isolated from outbred SD and F344-alb F344-congenic analbuminemic rats) as well as in their parent strains. After the rats were treated according to the Solt-Farber protocol [a single dose of diethylnitrosamine (DEN) followed by dietary 2-acetylaminofluorene (2-AAF) plus partial hepatectomy], F344 and F344-alb demonstrated similar numbers of much larger hyperplastic hepatic nodules (HPN) than SD or NAR, while in the latter two cases, sizes are approximately the same, NAR had a greater number of HPN. When HPN cells of F344 rats were infused into the portal vein of F344 and F344-alb, followed by treatment with the Solt-Farber protocol, the transplanted cells formed almost the same numbers of colonies of almost equal size within the livers in these two strains of rats. With continuous administration of a 2-acetylaminofluorene (2-AAF) diet, which can change the normally albumin-negative hepatocytes of analbuminemic rats to albumin-positive cells, this process occurred earlier in F344-alb than NAR, but almost the same numbers were reached after 30 days. The results demonstrate responses to significantly differ between NAR and F344-alb, with both resembling their parent strains to a large extent, indicating that genetic background has the major influence on susceptibility to hepatic carcinogenesis, rather than analbuminemia itself.

2-Acetylaminofluorene↗
PubMed1994

Further examples of evolution by gene duplication revealed through DNA sequence comparisons.

To test the theory that evolution by gene duplication occurs as a result of positive Darwinian selection that accompanies the acceleration of mutant substitutions, DNA sequences of recent duplication were analyzed by estimating the numbers of synonymous and nonsynonymous substitutions. For the troponin C family, at the period of differentiation of the fast and slow isoforms, amino acid substitutions were shown to have been accelerated relative to synonymous substitutions. Comparison of the first exon of alpha-actin genes revealed that amino acid substitutions were accelerated when the smooth muscle, skeletal and cardiac isoforms differentiated. Analysis of members of the heat shock protein 70 gene family of mammals indicates that heat shock responsive genes including duplicated copies are evolving rapidly, contrary to the cognitive genes which have been evolutionarily conservative. For the alpha 1-antitrypsin reactive center, the acceleration of amino acid substitution has been found for gene paris of recent duplication.

Actins↗
PubMed1994

Induction of the SOS response and mutations by reactive oxygen-generating compounds in various Escherichia coli mutants defective in the mutM, mutY or soxRS loci.

Derivatives of E. coli WP2s (uvrA trpE) defective in 7,8-dihydro-8-oxoguanine (8-OG) DNA glycosylase activity (mutM), MutY glycosylase activity on an A:8-OG mispair (mutY), and/or an adaptive response to oxidative stress by superoxide (soxRS) were constructed to compare the mutability to various reactive oxygen-generating compounds. Induction of Trp+ reversion was assayed both in the presence and absence of plasmid pKM101. Phenazine methosulfate and phenazine ethosulfate showed mutagenic activity at a relatively low dose in soxRS mutants. In comparison to the parent strain WP2s, however, the introduction of mutM, mutY, or soxRS mutations, in any combination, did not make the strain hypersensitive in terms of mutability (i.e. mutation induction at relatively low doses) to hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, or phenylhydrazine. Mutagenicity of formaldehyde was detected only in the pKM101-carrying strains. On the other hand, bleomycin, menadione, plumbagin, paraquat, and diquat were not mutagenic to any strain, with or without pKM101. The SOS-response inducing activity was measured by monitoring the expression of a umu'-'lacZ fusion gene, carried on the plasmid pSK1002. The induction of the SOS response by hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, formaldehyde, phenylhydrazine, and bleomycin was of almost the same magnitude between the parent strain and a mutM or soxRS mutant. Phenazine methosulfate and phenazine ethosulfate induced the SOS response only in the soxRS derivatives. No induction was detected by treatment with redox-cycling compounds, such as menadione, plumbagin, paraquat, or diquat.

Bacterial Proteins↗
PubMed1994

Essential role of arginine 235 in the substrate-binding of Lactobacillus plantarum D-lactate dehydrogenase.

Substitutions of the conserved Arg-235 with Lys and Gln induced drastic decreases in the catalytic efficiency of Lactobacillus plantarum D-lactate dehydrogenase (D-LDH). Both the mutant enzymes showed a marked resistance to 2,3-butanedione, by which the wild-type enzyme is rapidly inactivated unless NADH and oxamate are present. The pKa of the catalytic His was markedly shifted to the alkaline side by the Arg-to-Gln substitution, while it was not significantly shifted by the Arg to Lys substitution. The Arg-to-Lys replacement, by which the catalytic efficiency was less damaged, also induced decreases in kcat/Km for alternative substrates, such as 2-ketobutyrate, by approximately 10,000-fold, virtually the same level as in the case of pyruvate. Although both the wild-type and mutant enzymes exhibited lower kcat/Km for the alternative substrates than that for pyruvate, in the case of the mutant enzyme, the decrease in kcat/Km for the alternative substrates was mostly due to a decrease in kcat, while it was caused mainly by an increase in Km in the wild-type enzyme, suggesting that the mutant enzyme tends to form a nonproductive enzyme-substrate complex, in particular with more unfavorable substrates. The pH-dependence of the kinetic constants also indicated that there is a nonproductive binding that does not require the protonated or deprotonated form of the catalytic His residue. These results strongly suggest that Arg-235 plays an essential role in the tight and correct binding of substrate to the binding site of D-LDH, as in the case of Arg-171 in L-LDH.

Arginine↗
PubMed1994

Presence of pancreatic alpha-amylase, trypsinogen, and lipase immunoreactivity in normal human pancreatic ducts.

Presence of pancreatic alpha-amylase, trypsinogen, and lipase in normal pancreatic ducts was evaluated immunohistochemically in 10 surgically resected normal pancreatic specimens, using monoclonal antibodies against human pancreatic alpha-amylase, trypsinogen, and lipase. Immunoreactivity to all enzymes occurred patchily in some epithelial cells not only of the common bile duct and its periductal glands but also of the main and interlobular pancreatic ducts and periductal glands in the main pancreatic duct, as well as in pancreatic acinar cells. Ductal staining was fine-granular, and generally present in the supranuclear cytoplasm. Immunoreactivity was abolished by preabsorption. Centroacinar cells and intercalated and intralobular pancreatic ducts did not stain for any enzyme. These findings suggest that some epithelial cells of the large-sized pancreatic duct and its periductal glands express pancreatic alpha-amylase-, trypsinogen-, and lipase-like peptides, as do some epithelial cells of common bile duct and its periductal glands.

Adult↗
PubMed1994

Long-term follow-up study of 10 adolescent patients with sleep-wake schedule disorders.

Therapeutic trials for sleep-wake schedule disorders have been described, but a long-term follow-up of adolescents with such disorders have not previously been reported. We investigated 10 adolescents with sleep-wake schedule disorders who had formerly received intensive treatment. The investigation was carried out with detailed questionnaires about current sleep conditions and social state. The follow-ups were obtained from 1.2 to 11.2 years after the initial treatment. Three cases have remitted, and six have improved in illness severity. All patients showed improvement in social adaptation. Improvement in the social adaptation level was greater than improvement in the illness severity level. More cases should be studied to learn what factors influence the prognosis of these disorders.

Adolescent↗
PubMed1994

Ciliated carcinoma of the endometrium associated with mucinous and neuroendocrine differentiation: a case report with immunohistochemical and ultrastructural study.

A case of endometrial ciliated carcinoma mixed with foci of mucinous adenocarcinoma and argyrophil cells is described. The patient suffered from diabetes mellitus, hypertension and obesity, but had no history of estrogen use. Although the tumor presented well differentiated histologic features, it showed complete diffuse, endophytic extension. Approximately half of the cilia had abnormal inner structures, with 8 + 2 microtubular pattern. Some ciliated cells contained intracytoplasmic mucin, while others contained neurosecretory granules. These findings suggest that malignant ciliated cells have the capacity of further transformation into mucinous or endocrine cells.

Adenocarcinoma, Mucinous↗
PubMed1994

Neoplastic and non-neoplastic intermediate trophoblasts: an immunohistochemical and ultrastructural study.

Five cases of non-molar trophoblastic disease including one placental site trophoblastic tumor (PSTT), two exaggerated placental sites and two choriocarcinomas were compared with each other and with normal chorionic villi and placental site. This involved light microscopic, immunohistochemical and ultrastructural studies. Comparison of PSTT with choriocarcinoma suggested that the former represented a neoplastic transformation of placental site intermediate trophoblast. The PSTT showed a characteristic immunohistochemical distribution of human placental lactogen and human chorionic gonadotropin, resembling that of the placental site intermediate trophoblast. Placental site trophoblastic tumor cells were also characterized ultrastructurally by prominent perinuclear filaments, abundant rough endoplasmic reticulum, or both. Infiltrating intermediate trophoblasts in exaggerated placental sites were similar to PSTT cells rather than normal placental site intermediate trophoblasts. However cells with vacuolated cytoplasm or spindle-shaped intermediate trophoblastic cells were observed more frequently in the PSTT than the exaggerated placental sites. The intermediate trophoblastic cells in the choriocarcinomas showed a morphologically transitional form from cytotrophoblastic cell to syncytiotrophoblastic cell, but did not share unique ultrastructural similarities with placental site intermediate trophoblasts.

Adult↗
PubMed1994

All-or-nothing responses to carbachol in single intestinal smooth muscle cells of rat.

1. Concentration-response relationships for carbachol (CCh)-induced increases in the cytosolic calcium concentration ([Ca2+]i) and membrane currents were studied by use of fura-2 microfluorimetry and nystatin-perforated whole-cell recording in single smooth muscle cells isolated from rat intestine. 2. CCh produced an initial peak rise in [Ca2+]i followed by a small sustained rise. In individual cells, the peak rise in [Ca2+]i did not increase in amplitude even with increasing concentrations of CCh, though the threshold concentration varied in different cells. The initial peak rise in [Ca2+]i, but not the sustained rise, was due to the release of stored Ca2+, because it was unchanged after removal of external Ca2+ and the addition of nifedipine (1 microM) or La3+ (1 mM). 3. CCh elicited an outward and inward current in a cell dialyzed with a pipette solution containing KCl at a holding potential of -30 mV and with one containing NaCl at -60 mV, respectively. In individual cells, the amplitude of each current was similar in cells stimulated at over the threshold concentration of CCh, but the threshold was different among cells. 4. The percentage of cells showing Ca(2+)-transient responses to CCh at given concentrations was similar to those showing current responses and contractile responses. 5. In thin muscle bundles, a concentration-dependent contraction was evoked by CCh in the absence of external Ca2+. Its threshold was similar to those of Ca(2+)-transient and current responses in single cells. 6. These results suggest that CCh-induced release of stored Ca2+ takes place in an all-or-nothing fashion in individual cells of the rat intestinal smooth muscle.

Animals↗
PubMed1994

Inhibitory effects of caffeine on secretagogue-induced catecholamine secretion from adrenal chromaffin cells of the guinea-pig.

1. The inhibitory action of caffeine on catecholamine secretion induced by secretagogues was investigated in perfused adrenal glands and dispersed chromaffin cells of the guinea-pig. 2. Caffeine (10 mM) caused a reversible inhibition of catecholamine secretion evoked by acetylcholine (ACh, 50 microM), KCl (56 mM, high K+) and veratridine (100 microM) and that induced by muscarinic receptor activation in the absence of extracellular Ca2+ in perfused adrenal glands. 3. In dispersed chromaffin cells, caffeine caused a dose-dependent inhibition of the secretory responses to 100 microM ACh and veratridine. Forskolin (30 microM), dibutyryl cyclic AMP (1 mM) and 8-bromo cyclic AMP (1 mM) did not mimic the action of caffeine. 4. In the voltage-clamp, whole-cell recording mode (at a holding potential of -60 mV or -70 mV), ACh (100 microM) evoked an inward current, and depolarizing pulses elicited inward Na+, Ca2+ and outward K+ currents. All these responses were partially inhibited by caffeine (20 mM). 5. ACh rapidly increased the intracellular concentration of Ca2+ ([Ca2+]i) in fura-2-loaded cells in either the presence or the absence of external Ca2+, though its magnitude was decreased by about 50% in Ca(2+)-free conditions. Caffeine (20 mM) inhibited these ACh-induced increases in [Ca2+]i. 6. In permeabilized chromaffin cells, caffeine (20 mM) caused an inhibition of catecholamine secretion evoked by Ca2+ (10 microM). 7. These results suggest that caffeine inhibits evoked catecholamine secretion through mechanisms such as the blockade of voltage-dependent Na+ and Ca2+ currents and ACh receptor current, and reduction of the release of intracellularly stored Ca2+ and/or Ca(2+)-sensitivity of the secretory apparatus.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Lysophosphatidylcholine, a component of stromal phospholipids, as a candidate vasoconstrictive factor in stroma-free hemoglobin.

Stroma-free hemoglobin (SFH) contains a trace amount of phospholipids, which has been implicated in the toxic reactions associated with SFH. We analyzed stromal phospholipids by high-performance liquid chromatography and found that SFH contained small quantities of lysophosphatidylcholine (LPC), which is known to be capable of producing a defect in endothelium-dependent arterial relaxation, in addition to major classes of constituent phospholipids in red cell membrane. LPC content was determined to be 1.65 nmol/ml (hemoglobin 8.1 g/dl). To evaluate the role of these stromal phospholipids in SFH-induced vasoconstriction, we next examined the effect of lipids on vascular tone in rabbit aortic strips. Preincubation with the crude lipid extract or the LPC purified from SFH significantly inhibited acetylcholine-induced relaxation in phenylephrine-precontracted tissues. The LPC-induced inhibition was reversed by incubation of the tissues in the absence of lipids, indicating the functional integrity of endothelium. From these results, we propose a possibility that LPC, a component of stromal phospholipids, is a candidate for vasoconstrictive factors present in SFH.

Acetylcholine↗
PubMed1994

Molecular cloning of two new heat shock genes related to the hsp70 genes in Staphylococcus aureus.

We have identified two new heat shock protein genes, orf37 and orf35, in Staphylococcus aureus, located upstream and downstream of grpE(hsp20), dnaK(hsp70), and dnaJ(hsp40) homologous genes in the order orf37-hsp20-hsp70-hsp40-orf35. The transcripts of both orf37 and orf35 were increased by thermal upshift of the culture from 37 to 46 degrees C. The heat shock promoters were located upstream of orf37 and upstream of hsp40. The deduced peptide of orf37 showed similarity with those of orfA in Clostridium acetobutylicum and orf39 in Bacillus subtilis. orf35 was unique in S. aureus and has not yet been described in other bacteria.

Amino Acid Sequence↗