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K Tamura

Publications and source records attributed to K Tamura.

At least 829 records · Page 46Linked to original sources
PubMed1992

In vitro study of E.coli tRNA(Arg) and tRNA(Lys) identity elements.

Various tRNA transcripts were constructed to study the identity elements of E.coli tRNA(Arg) and tRNA(Lys). Exchange of the anticodon of the major tRNA(Arg) from ACG to either CCG or CCU did not result in a significant loss of arginine acceptor activity, whereas not only that to UUU but also that to ACA or ACC decreased the activity. Base substitutions and deletion at A20 also impaired the arginine charging activity by over 50-fold. Arginine charging activity was introduced by either substitution of the anticodon from UAC to ACG in tRNA(Val) or from UUU to UCU in tRNA(Lys). Only a single base substitution at the third position of tRNA(Trp) anticodon (CCA) from A to G also gave rise to arginine charging activity, which was elevated to a comparable level to that of the tRNA(Arg) transcript by an additional A20 insertion. Base substitutions of the major tRNA(Arg) at the discriminator position into pyrimidines led to a decrease by factors of three to four. These data show that the third letter of the anticodon G36 or U36 besides the second letter C35 and the A20 in the variable pocket is responsible for the arginine acceptor identity, to which the discriminator base A73 or G73 contributes in an auxiliary fashion. In contrast to the arginine system, the transcript with the wild-type tRNA(Lys) sequence showed only 140-fold lower lysine charging activity than the native tRNA(Lys), suggesting the involvement of base modifications in recognition. Replacement of the anticodon UUU with not only UCU and UAC but also UUA and UUC seriously affected the lysine acceptor activity, and those with GUU and UUG also decreased by factors of 17 and 5, respectively. Introduction of UUU into the anticodons conferred lysine charging activity upon both tRNA(Val) and tRNA(Arg). Substitution of the discriminator base A73 by any of the other bases decreased the lysine acceptor activity by a factor of ten. These results indicate the involvements of all the three bases of the anticodon and A at the discriminator position in lysine specific aminoacylation.

Anticodon↗
PubMed1992

An oxidized analog of alpha-human atrial natriuretic polypeptide is a selective agonist for the atrial-natriuretic-polypeptide clearance receptor which lacks a guanylate cyclase.

The differences in biological functions between alpha-human atrial natriuretic polypeptide (alpha-hANP) and its oxidized analog, MetSO-alpha-hANP, have been investigated. Analysis of the ANP receptor subtypes by affinity labeling has shown that a bovine pulmonary aortic endothelial cell line (CPAE cells) primarily expresses ANP-R1 (R, receptor) coupled to particulate guanylate cyclase, while Hela cells from human cervical carcinoma predominantly express ANP-R2, which lacks a guanylate cyclase. alpha-hANP could bind to both ANP receptor subtypes with high affinity, while MetSO-alpha-hANP showed more selective binding to ANP-R2 than to ANP-R1. The activity of MetSO-alpha-hANP for stimulation of guanylate cyclase coupled to ANP-R1 was about 520-fold less than that of alpha-hANP (median effective dose = 2.5 nM for alpha-hANP, 1.3 microM for MetSO-alpha-hANP), indicating that MetSO-alpha-hANP was a partial agonist for this receptor. While this oxidized analog could inhibit the cAMP production through ANP-R2, with 0.15 times the activity of alpha-hANP (median concentration = 0.31 nM for alpha-hANP, 2.0 nM for MetSO-alpha-hANP). In in vivo studies, the diuretic activity of MetSO-alpha-hANP was 25-100-fold less than that of alpha-hANP. In addition, MetSO-alpha-hANP could potentiate the diuretic activity of alpha-hANP that was also caused by C-ANF4-23, a specific agonist for ANP-R2. These results demonstrate that MetSO-alpha-hANP can act as an agonist more selective for ANP-R2 than for ANP-R1, both in vivo and in vitro. The relationship between receptor selectivities and the conformation of alpha-hANP or MetSO-alpha-hANP was also discussed.

Affinity Labels↗
PubMed1992

Regulation of activin beta A mRNA level by cAMP.

We demonstrated the presence of five species of the activin beta A mRNA in human placenta and one major RNA associated with two minor RNAs of the activin in the fetal membrane. We investigated the effect of 8-bromo-cAMP (8-Br-cAMP) on accumulation of activin beta A subunit mRNA in human fibrosarcoma HT1080 cells. Although low levels of the activin mRNA were detectable in the untreated cells, the one main RNA species was predominantly accumulated by 8-Br-cAMP. We propose that generation of multiple activin mRNAs in the fetal membrane and cAMP-treated HT1080 cells is presumably due to a cell-specific alternative polyadenylation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Inhibitory and stimulatory actions of danazol in rat ovarian and uterine tissues.

We examined whether danazol has a direct action on ovarian steroid secretion and/or uterine prostaglandin (PG) F2 alpha catabolic activity in immature rats in which the first ovulation was induced and in adult ovariectomized rats. The preovulatory surge of estradiol and progesterone was markedly suppressed together with that of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by danazol administration under conditions that blocked the first ovulation. Uterine weight and PGF2 alpha catabolic activity enhanced by endogenous estrogen were greatly decreased by danazol treatment at a dose that did not block the first ovulation in immature rats. When danazol (30 mg) was given s.c. once daily for 2 days to ovariectomized rats, the uterine weight and PGF2 alpha catabolic activity per uterus were clearly increased, and the compensatory increase in FSH levels as a result of castration was not influenced, although the compensatory increase in LH levels was inhibited. These results demonstrate that danazol has a direct action on the ovary and uterus, and give further support to the view put forward in our previous paper that these actions of danazol may contribute to its therapeutic effects.

Administration, Oral↗
PubMed1992

The role of anticodon bases and the discriminator nucleotide in the recognition of some E. coli tRNAs by their aminoacyl-tRNA synthetases.

The T7 polymerase transcription system was used for in vitro synthesis of unmodified versions of the E. coli tRNA mutants that insert asparagine, cysteine, glycine, histidine, and serine. These tRNAs were used to qualitatively explore the role of some anticodon bases and the discriminator nucleotide in the recognition of tRNA by aminoacyl-tRNA synthetases. Coupled with data from earlier studies, these new results essentially complete a survey of all E. coli tRNAs with respect to the involvement of anticodon bases and the discriminator nucleotide in tRNA recognition. It is found that in the vast majority of tRNAs both of these elements are significant components of tRNA identity. This is not universally true, however. Anticodon sequences are unimportant in tRNA(Ser), tRNA(Leu), and tRNA(Ala) while the discriminator base is inconsequential in tRNA(Ser) and tRNA(Thr). The significance of these results for origin-of-life studies is discussed.

Amino Acyl-tRNA Synthetases↗
PubMed1992

Analysis of prognostic factors in patients with hepatocellular carcinoma treated by transcatheter arterial embolization.

We studied 240 cases of unresected hepatocellular carcinoma (HCC) using Cox's proportional hazard model to elucidate which factors would be closely related with the survival period after treatment by transcatheter arterial embolization (TAE) in the presence or absence of iodized oil. The results were as follows. The cumulative survival values obtained after TAE were 67.5% for 1 year, 32.0% for 2 years, and 20.5% for 3 years. The most significant prognostic factor was the degree of extension of tumor embolus in the portal vein or its branch. The tumor extension and the tumor type were also important factors. Age, sex, and AFP, HBsAg, and HCV Ab values were not useful as prognostic factors. This study provides a rational background for the selection of treatment for HCC. Furthermore, knowledge of the prognostic factors is useful for the management of patients, particularly in maintaining their good quality of life.

Adult↗
PubMed1992

Effects of prolonged exposure to histamine on guinea pig intestinal neurons.

Intracellular microelectrodes were used to study the effects of prolonged exposure to histamine on the electrophysiological behavior of AH/type-2 neurons in the myenteric plexus of the guinea pig small intestine. Application of histamine activated H2 receptors to convert the neurons to a heightened state of excitability. Heightened excitability was evident as repetitive spike discharge made possible, in part, by suppression of postspike after-hyperpolarization. The hyperexcitable state persisted unchanged for prolonged periods of 4.5 hr in the continued presence of histamine, suggesting that desensitization may never occur in vivo. The results are interpreted as a neural correlate for the pathophysiology associated with microscopic colitis and other inflammatory conditions involving mast cell hyperplasia.

Animals↗
PubMed1992

Evidence for a role of free radicals by synthesized scavenger, 2-octadecylascorbic acid, in cerulein-induced mouse acute pancreatitis.

To define the role of free radicals and of lipid peroxide involvement during the progress of cerulein-induced acute pancreatitis in mice, we evaluated the effect of a novel free radical scavenger, 2-octadecylascorbic acid (CV-3611), on pancreatic edema formation, and the levels of serum enzymes (amylase, lipase) and of lipid peroxide in pancreatic tissue. Mice were divided into three groups: control group, intraperitoneal injection of saline only; pancreatitis group, cerulein 50 micrograms/kg injected intraperitoneally six times at 1-hr intervals; treatment groups, CV-3611 10 mg/kg subcutaneously just after intraperitoneal cerulein injection. After the cerulein injection, the degree of pancreatic edema formation, serum amylase and lipase levels, and the amount of lipid peroxide in pancreatic tissue increased significantly during the observation period of 12 hr. Treatment with CV-3611 resulted in significant reduction in pancreatic edema formation at 3.5 hr (P less than 0.05) and 9 hr (P less than 0.05), serum amylase and lipase levels at 3.5 hr (P less than 0.05) and 12 hr (P less than 0.05), and lipid peroxide levels at 3.5 hr (P less than 0.05), 6 hr (P less than 0.05) and 12 hr (P less than 0.05). These results indicate that a novel free radical scavenger, CV-3611, has a strong therapeutic effect during the development of acute pancreatitis and suggest that oxygen-derived free radicals play an important role in the pathogenesis of acute pancreatitis.

Acute Disease↗
PubMed1992

A transient rise in plasma beta-endorphin after a traditional 47 degrees C hot-spring bath in Kusatsu-spa, Japan.

To clarify the mechanism of the intoxicating feeling attained after a traditional 47 degrees C hot-spring bath called 'jikan-yu' in Kusatsu-spa, Japan, we examined the change in plasma levels of beta-endorphin and methionine enkephalin in 7 healthy subjects. The mean sublingual temperature rose from 36.8 degrees C to 38.6 degrees C and the plasma beta-endorphin level from 16.2 pg/ml to 49.5 pg/ml 2 minutes after completing a 3-minute bath in 47 degrees C hot-spring water. However, the plasma methionine enkephalin level was not changed. This feeling of intoxication may be explained by the transient rise in plasma beta-endorphin level.

Adult↗
PubMed1992

Inhibitory effect of dietary iron deficiency on inductions of putative preneoplastic lesions as well as 8-hydroxydeoxyguanosine in DNA and lipid peroxidation in the livers of rats caused by exposure to a choline-deficient L-amino acid defined diet.

Effects of dietary iron deficiency on inductions of putative preneoplastic lesions and oxidative alterations in the livers of rats by a choline-deficient L-amino acid defined (CDAA) diet were examined. Male Fischer 344 rats, 4 weeks old, were used with a total experimental period of 16 weeks, consisting of 4-week pretreatment and 12-week treatment periods (periods A and B respectively). During period A, a choline-supplemented L-amino acid defined (CSAA) or an iron-deficient CSAA diet was administered, and the CDAA or an iron-deficient CDAA diet was fed in period B. Formation of 8-hydroxydeoxyguanosine (8OHdG), a DNA adduct generated by activated oxygen species, in DNA and lipid peroxidation in liver cell membranes were sequentially determined after the beginning of period B. At the end of the experiment, development of gamma-glutamyltransferase (GGT) and glutathione S-transferase placental form (GSTP) positive liver lesions were quantitatively analysed. In the animals fed the CDAA diet, formation of 8OHdG and lipid peroxidation increased with time, and GGT and GSTP positive liver lesions developed. Formation of 8OHdG, lipid peroxidation and the numbers of induced enzyme-altered liver lesions were all reduced in rats fed the iron-deficient CSAA diet in period A and/or the iron-deficient CDAA diet in period B. The present results indicate that iron plays an important role in induction of preneoplastic liver lesions in rats caused by exposure to the CDAA diet possibly in connection with its known catalytic role in generation of highly reactive activated oxygen species.

Amino Acids↗
PubMed1992

Effects of isoprenaline and ouabain on cytosolic calcium and cell motion in single rat cardiomyocytes.

OBJECTIVE: The aim was to develop a novel system to measure changes in cytosolic free calcium concentration ([Ca2+]i) and cell motion simultaneously in a single beating myocyte by digital imaging microscopy. METHODS: Indo-1 was selected as a fluorescent calcium indicator. The particular feature of our digital imaging microscopy is that, in order to avoid cell movement artifacts, two indo-1 fluorescence images of different wavelengths are obtained at the same time at 16.7 ms intervals using two SIT cameras. Isolated ventricular myocytes were used, prepared from hearts of male Sprague-Dawley rats, weighing 350 to 400 g. RESULTS: In continuously beating cells contracted by electrical field stimulation, we can visualise changes in [Ca2+]i and cell shape during contraction with pseudocolour images of the fluorescence ratios, and it was found that the onset of the calcium transient preceded that of the shortening of cell length. Both isoprenaline and ouabain enhanced the magnitudes of the calcium transient and cell contraction. Furthermore, isoprenaline shortened the half decay time of the calcium transient. CONCLUSIONS: Our data suggest that the newly developed system is useful for measuring rapid changes in [Ca2+]i in relation to cell motion, and is particularly suitable for measuring the calcium transients in a beating cardiomyocyte.

Animals↗
PubMed1992

Shigella and enteroinvasive Escherichia coli infections in households of children with dysentery in Bangkok.

Shigellae and enteroinvasive Escherichia coli (EIEC) were identified in children with dysentery and their household contacts in Bangkok. Shigellae were isolated from 49% and EIEC from 6% of 306 children with dysentery seen at the outpatient department of Children's Hospital on weekdays during January through June 1989 and October 1989 through October 1990. The same serotype infecting the index child was isolated from 21 (4%) of 522 household contacts of 151 index children with Shigella infections and from none of 60 household contacts of 19 index children with EIEC infections. Amplification of DNA sequences coding for the invasion-associated locus (ial) by polymerase chain reaction increased the identification of Shigella and EIEC infections from 57% (111/193) to 68% (132/193). ial sequences were identified in 3 of 20 drinking water specimens from which shigellae or EIEC were not isolated. Amplification of ial sequences identified more shigellae and EIEC than did bacteriologic and colony hybridization methods in children with dysentery and in drinking water in Bangkok.

Adolescent↗
PubMed1992

Localized, aggregative, and diffuse adherence to HeLa cells, plastic, and human small intestines by Escherichia coli isolated from patients with diarrhea.

Adherence of diarrhea-associated Escherichia coli was studied by scanning electron microscopy. Enteropathogenic E. coli (EPEC) adherence factor-positive (EAF+) E. coli of EPEC serotypes (class I EPEC) adhered to plastic and human jejunal and ileal mucosa, similar to case and HeLa cells. Localized adherence, elongation of cell microvilli, and "locking" of the bacterial aggregates by the elongated microvilli were evident after incubation for 20 min. EAF+ E. coli adhered strikingly to mucus but rarely to M cells in Peyer's patch-associated epithelium. Most enteroaggregative E. coli (EAggEC) strains adhered to plastic, similar to HeLa cells. Some diffuse-adhering E. coli (DAEC) strains displayed no adherence to plastic but formed "dimples" on HeLa cells. Both EAggEC and DAEC adhered at lower levels to human small intestines (except M cells) than did EAF+ E. coli. In all cases of EAF+ E. coli, EAggEC, and DAEC, strains were found with atypical characteristics. The data demonstrate the unique adherence characteristics of EAF+ E. coli, EAggEC, and DAEC.

Adhesins, Escherichia coli↗
PubMed1992

Estimation of the number of nucleotide substitutions when there are strong transition-transversion and G+C-content biases.

A simple mathematical method is developed to estimate the number of nucleotide substitutions per site between two DNA sequences, by extending Kimura's (1980) two-parameter method to the case where a G+C-content bias exists. This method will be useful when there are strong transition-transversion and G+C-content biases, as in the case of Drosophila mitochondrial DNA.

Animals↗
PubMed1992

The rate and pattern of nucleotide substitution in Drosophila mitochondrial DNA.

The nucleotide sequences of a segment of mitochondrial DNA (mtDNA) have been determined for nine species or subspecies of the subgenus Drosophila of the genus Drosophila. This segment contains two complete protein-coding genes (i.e., NADH dehydrogenase subunit 1 and cytochrome b) and a transfer RNA gene (tRNA(ser)). The G+C content at third-codon positions for the two protein-coding genes was 1.5 times higher than that in the D. melanogaster species group, which belongs to the subgenus Sophophora. However, there was a substantial difference between the nucleotide frequencies of G and C. The number of nucleotide substitutions per silent site was more than three times higher than that for nuclear DNA, although it was only 60% of that for mammalian mtDNA. Both parametric and nonparametric analyses revealed a strong transition-transversion bias in nucleotide substitution, as was observed in mammalian mtDNA. Moreover, the rate of substitution of A and T for G and C is higher than that for the opposite direction. This bias seems to be responsible for the extremely A+T-rich base composition of Drosophila mtDNA. It is also noted that the rate of transitional change between A and G is higher than that between T and C.

Animals↗
PubMed1992

Heterotopic autotransplantation of the distal pancreas segment after total pancreatectomy for cancer of the head of the pancreas.

Autotransplantation of the distal pancreas segment with pancreaticojejunostomy was performed in four patients with cancer of the head of the pancreas to preserve endocrine pancreatic function after extended total pancreatectomy. All patients had tumor involvement of both the celiac axis and the portal vein. The pancreatic graft was determined to be cancer-free by frozen section histologic and pancreatic juice cytologic examinations. The distal pancreas segment was autotransplanted to the iliac vessels heterotopically and placed in the extraperitoneal pocket to avoid untoward effects of any local recurrence or pancreatic leakage. This procedure, in the form of reconstruction, might be called modified subtotal pancreatoduodenectomy. Postoperatively, all patients remained normoglycemic without exogenous insulin administration, and their quality of life was considered satisfactory.

Aged↗