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Biomedical subjects

K Nagata

Publications and source records attributed to K Nagata.

At least 847 records · Page 47Linked to original sources
PubMed1988

Colloidal volume expansion during acute cerebral ischaemia: assessed by local cerebral blood flow and computerized power ratio index.

Colloidal volume expansion during acute cerebral ischaemia was assessed by local cerebral blood flow (CBF) and the power ratio index (PRI) in 8 anaesthetized Macaque monkeys. Focal cerebral ischaemia was produced by right middle cerebral artery occlusion. The animals were then volume expanded (to maximum cardiac output) with 6% hetastarch and then exsanguinated to baseline cardiac output. During volume expansion, local CBF in the ischaemic hemisphere increased from 25 +/- 12 to 39 +/- 23 cc/100 g/min (p less than 0.01) and during exsanguination decreased to 32 +/- 18 cc/100 g/min. Local CBF did not change significantly in the nonischaemic hemisphere. EEG power data, as assessed by PRI [(delta + theta power/alpha + beta power) x 100] changed significantly during blood volume manipulation. The mean PRI value in the right hemisphere deteriorated by increasing from 65 +/- 22 to 94 +/- 25 (p less than 0.01) following vessel occlusion but improved by decreasing to 81 +/- 23 (p less than 0.05) following volume expansion. Following exsanguination, the PRI value increased to 87 +/- 21. These data demonstrate the benefits of volume expansion during acute cerebral ischaemia. Changes in local CBF were consistently associated with changes in the PRI maps and values.

Animals↗
PubMed1988

Receptor current fluctuation analysis in the labellar sugar receptor of the fleshfly.

Fluctuations in the receptor current of the labellar sugar receptor of the fleshfly were analyzed. The receptor current was recorded extracellularly as a drop in potential between the tip and the base of the taste sensillum. After treatment with tetrodotoxin, the taste cells completely lost their impulses but retained their receptor currents, thus facilitating analysis of the receptor current without disturbance by impulses. The current fluctuation increased markedly when the sensillum was stimulated with effective sugars: maltose, sucrose, and fructose. The fluctuation increased in parallel with development of the receptor current, which indicates that it occurs as soon as the sugar reaches the apex of the sensory process. Analysis of fluctuations by computation of autocorrelation functions (ACFs) or power spectra (PS) revealed that: (a) the variance (mean square) of fluctuation vs. sugar concentration curve reached a maximum, in contrast to the monotonic increase shown by the receptor current; (b) the ACF was approximated by an exponential term, and its time constant differed according to the sugars used and their concentrations. The time constants for fructose and maltose decreased with increases in sugar concentration. At the concentrations of sugars evoking the same magnitude of receptor current, the time constant for fructose was the largest and that for maltose was the smallest. It was strongly suggested that transduction ion channels are present at the tip region of the sensory process of the sugar receptor cell and are operated directly by sugars.

Animals↗
PubMed1988

Purification and characterization of an acidic amino acid specific endopeptidase of Streptomyces griseus obtained from a commercial preparation (Pronase).

A protease was purified 163-fold from Pronase, a commercial product from culture filtrate of Streptomyces griseus, by a series of column chromatographies on CM-Toyopearl (Fractogel), Sephadex G-50, hydroxyapatite, and Z-Gly-D-Phe-AH-Sepharose 4B using Boc-Ala-Ala-Pro-Glu-pNA as a substrate. The final preparation was homogeneous by polyacrylamide gel electrophoresis (PAGE), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and gel isoelectric focusing. Studies on the substrate specificity with peptide p-nitroanilides revealed that this protease preferentially hydrolyzed peptide bonds on the carbonyl-terminal side of either glutamic acid or aspartic acid. It was most active at pH 8.8 for the hydrolysis of Boc-Ala-Ala-Pro-Glu-pNA. The molecular weight of the protease was estimated to be 20,000 by gel filtration on Sepharose 6B using 6 M guanidine hydrochloride as an eluent, and 22,000 by SDS-PAGE in the presence of 2-mercaptoethanol. The isoelectric point of the enzyme was 8.4. The enzyme was inactivated by diisopropyl phosphofluoridate (DFP) but not by p-chloromercuribenzoate (PCMB) or EDTA.

Amino Acids↗
PubMed1988

A sex-specific form of cytochrome P-450 catalyzing propoxycoumarin O-depropylation and its identity with testosterone 6 beta-hydroxylase in untreated rat livers: reconstitution of the activity with microsomal lipids.

Characteristics of a typical male-dominant reaction, dealkylation of n-propoxycoumarin, in rat livers were studied in relation to microsomal testosterone 6 beta-hydroxylase. The depropylation was more than 10-fold higher in the liver of male than female adult rats, but the sex-related difference was eliminated by neonatal castration. Hypophysectomy of adult male rats, which decreased the rates of male-specific P-450-male-dependent reactions, increased the depropylation of propoxycoumarin, while the rate was decreased by either intermittent injection or continuous infusion of human growth hormone to hypophysectomized rats. With regard to age-related difference, microsomal depropylation was detectable at neonate and reached a maximal level at 14 to 20 d of age, but was abruptly diminished only in female rats at puberty. These changes are in good agreement with those of testosterone 6 beta-hydroxylation and the content of a male-specific P-450(6)beta-1/PB-1. In reconstituted systems using extracted microsomal lipids, P-450(6)beta-1/PB-1 and P-450-male catalyzed the depropylation of propoxycoumarin. However, the microsomal depropylation was inhibited by antibodies which recognize P-450(6)beta-1/PB-1, but not P-450-male. These results indicate that microsomal depropylation of propoxycoumarin is catalyzed mainly by a male-specific P-450(6)beta-1/PB-1 in livers of untreated rats.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1988

RNA polymerase of influenza virus: role of NP in RNA chain elongation.

Ribonucleoprotein (RNP) cores of influenza virus A/PR/8/34 were dissociated into RNA polymerase (PB1-PB2-PA complex)-associated genome RNA and nuclear protein (NP) fractions by CsCl centrifugation. The RNA polymerase-RNA complexes were capable of catalyzing the endonucleolytic cleavage of capped RNA, the initiation of primer-dependent RNA synthesis, and the synthesis of small-sized RNA, but were unable to synthesize template-sized RNA. By adding the NP protein to the RNA polymerase-RNA complexes, RNP (RNA polymerase-RNA-NP) complexes were reconstituted; they synthesized template-sized transcripts as did native RNP cores. These observations are consistent with the model where viral RNA polymerase is composed of the three P proteins while NP is essential for the elongation of RNA chains. RNP was completely dissociated into RNA-free proteins (PB1, PB2, PA, and NP) and a protein-free genome RNA fraction by centrifugation in cesium trifluoroacetate (CsTFA) and glycerol. By mixing the protein and RNA fractions, primer-dependent RNA-synthesizing activity was regained. These complexes, however, produced only small-sized RNA, presumably due to incorrect assembly of NP on viral RNA.

DNA-Directed RNA Polymerases↗
PubMed1988

Relationship between the in vitro sensitivity to cytosine arabinoside of blast progenitors and the outcome of treatment in acute myeloblastic leukaemia patients.

The sensitivity to cytosine arabinoside (Ara-C) of blast progenitors from 22 acute myeloblastic leukaemia (AML) patients was studied in methylcellulose and suspension cultures. Primary colony-formation (PE1) in methylcellulose reflects the terminal divisions of blast progenitors, while secondary colony formation (PE2) in methylcellulose and the clonogenic cells recovery in suspension are considered to be based on the self-renewal of blast progenitors. In any patient, PE2 or clonogenic cells in suspension were more sensitive to Ara-C than PE1. The results indicate that Ara-C effectively suppresses not only terminal divisions but also self-renewal of blast progenitors D10 Ara-C value, the dose required to reduce survival to 10% of control, for PE1, PE2 and clonogenic cells in suspension showed marked patient-to-patient variation. No significant correlation was found between D10 Ara-C in methylcellulose or suspension culture and the response to treatment with a combination chemotherapy of 6-mercaptopurine, Ara-C and daunorubicin. However, a relapsed patient whose D10 values in methylcellulose and suspension cultures were very high showed poor response to a high-dose Ara-C protocol, where Ara-C was given alone at a high dose. The application of chemosensitivity test as a prediction of the clinical outcome may be dependent on the treatment protocol.

Adult↗
PubMed1988

Viral RNA polymerases.

Recent progress in molecular biological techniques revealed that genomes of animal viruses are complex in structure, for example, with respect to the chemical nature (DNA or RNA), strandedness (double or single), genetic sense (positive or negative), circularity (circle or linear), and so on. In agreement with this complexity in the genome structure, the modes of transcription and replication are various among virus families. The purpose of this article is to review and bring up to date the literature on viral RNA polymerases involved in transcription of animal DNA viruses and in both transcription and replication of RNA viruses. This review shows that the viral RNA polymerases are complex in both structure and function, being composed of multiple subunits and carrying multiple functions. The functions exposed seem to be controlled through structural interconversion.

DNA-Directed RNA Polymerases↗
PubMed1988

[Studies of the factors affecting the reduction of chronic subdural hematoma: effect of preoperative factors with special reference to cerebral atrophy].

The authors examined the preoperative factors affecting the reduction of chronic subdural hematoma (CSDH). A new method was developed to calculate the reduction rate of CSDH using CT volumetry technique. Postoperative serial CT films were examined and each hematoma volume was calculated by microcomputer. A postoperative exponential decrease of hematoma volume was observed, and the log-transformation of the hematoma volume turned the curve to a linear decrease. The least square method was used to fit an exponential curve, and the half reduction date (HRD) was calculated from the fitting curve. This HRD represents a mathematical indicator of the reduction rate of CSDH. Using this technique, the relationships between this HRD and the following parameters were examined in 61 patients. The preoperative factors examined are as follows; 1) patient's age, 2) preoperative hematoma volume, 3) CT number of the hematoma, 4) time interval between the head injury and the onset of symptom, and 5) the degree of cerebral atrophy. The degree of cerebral atrophy was calculated by means of a simple approximate formula as described by one of the authors (K.N.). Patient's age and the hematoma volume were correlated with HRD, and the correlation coefficients were 0.346 (p less than 0.01) and 0.298 (p less than 0.05) respectively. On the other hand, preoperative CT findings and the duration from the trauma had no correlation with HRD. Cerebral atrophy has hitherto been thought to affect the reduction of hematoma. However, our quantitative study revealed no correlation between cerebral atrophy and the reduction of hematoma rate. This unexpected result may be attributed to the difference between cerebral atrophy and cerebral elasticity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗