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Biomedical subjects

H Tokunaga

Publications and source records attributed to H Tokunaga.

At least 163 records · Page 9Linked to original sources
PubMed1986

Significance of the increase in glucose 6-phosphatase activity in skeletal muscle cells of the mouse by starvation.

The effects of starvation on glucose 6-phosphatase (G6Pase; EC 3.1.3.9., D-glucose 6-phosphate phosphohydrolase) and glycogen phosphorylase (EC 2.4.1.1.) activities, and on glycogen content, were studied in skeletal muscles (m. rectus femoris) of mice. In the muscle cells from fed animals, the cytochemical reaction product for G6Pase activity was observed in moderate amounts in the terminal cisternae of sarcoplasmic reticulum and in small amounts in the nuclear envelope, and was rare or absent in the intermyofibrillar sarcoplasmic reticulum. After 4 days of starvation, however, the reaction product became abundant in all of the terminal cisternae, intermyofibrillar sarcoplasmic reticulum, and nuclear envelope. Biochemical G6Pase and glycogen phosphorylase a (active form) activities were higher in the muscles of starved mice than in those of fed animals. The glycogen content decreased markedly in the muscles of starved mice. The results suggest that the role of the increased G6Pase in skeletal muscle cells of starved mice is to release glucose into the blood by hydrolyzing glucose 6-phosphate produced through the increased phosphorylase activity.

Animals↗
PubMed1984

Studies on the modification and processing of prolipoprotein in Escherichia coli. Effects of structural alterations in prolipoprotein on its maturation in wild type and lpp mutants.

We have previously shown that an Escherichia coli mutant ( mlpA allele) containing a structurally altered murein prolipoprotein due to substitution of Gly14 by Asp14 , is globomycin resistant. In addition, the mutant prolipoprotein is not modified with glyceride and consequently remains uncleaved. Spontaneous revertants possessing a mature lipoprotein of apparent normal structure can be isolated by EDTA selection. Three revertants were chosen in the present study which included the analysis of kinetics of lipoprotein maturation and the determination of globomycin sensitivity. These pseudorevertants in the lpp gene which could be recognized by the anomalous prolipoprotein mobility in sodium dodecyl sulfate gels, exhibited altered globomycin sensitivity in vivo. Our results indicate that alterations in prolipoprotein structure affect the kinetics of prolipoprotein modification and processing reactions, both in vivo and in vitro. Pulse-chase experiments revealed the transient existence of unmodified prolipoprotein and modified prolipoprotein as biosynthetic intermediates of mature lipoprotein. The rate of prolipoprotein modification appeared to be slightly faster than that of processing in the wild type cell. In contrast, modification of prolipoprotein was rate limiting in a pseudorevertant strain 14R21 , and the processing of 14R21 modified prolipoprotein appeared to proceed more rapidly than that of wild type prolipoprotein, both in vitro and in vivo.

Anti-Bacterial Agents↗
PubMed1984

Properties of chemically modified porin from Escherichia coli in lipid bilayer membranes.

Purified porin OmpF from Escherichia coli outer membrane was chemically modified by acetylation and succinylation of amino groups and by amidation of the carboxyl groups. Native and chemically modified porins were incorporated into lipid bilayer membranes and the permeability properties of the pores were studied. Acetylation and succinylation of the porin trimers had almost no influence on the single channel conductance in the presence of small cations and anions and the cation selectivity remained essentially unchanged as compared with the native porin. Amidation had also only little influence on the single channel conductance and changed the pore conductance at maximum by less than 50%, whereas the cation selectivity of the porin is completely lost after amidation. The results suggest that the structure of the porin pore remains essentially unchanged after chemical modification of the pores and that their cation selectivity is caused by an excess of negatively charged groups inside the pore and/or on the surface of the protein. Furthermore, it seems very unlikely that the pore contains any positively charged group at neutral pH.

Acetylation↗
PubMed1984

[Acinic cell carcinoma of the trachea--a case report].

A 27-year-old woman was admitted to our hospital complaining of dyspnea. Bronchoscopic examination revealed an endotracheal mass in the lower trachea. Endoscopic removal of the lesion was done by the electrocoagulation method followed by wide circumferential excision and reconstruction of the trachea three days later. The patient made an uneventful recovery and has had no recurrence in two years of follow-up. The diagnosis of acinic cell carcinoma was made by light microscopy. This is the first description, to our knowledge, of a primary neoplasma of the intrathoracic trachea having the histological appearance of a salivary gland acinic cell tumor.

Adult↗
PubMed1984

Mechanisms of specific change by estradiol in sensitivity of rat uterus to serotonin.

The sensitivity (contractile response) to serotonin (5-HT) of the isolated rat uterus was increased either during estrus or by administration of estradiol to ovariectomized rats. These increases in sensitivity to 5-HT were specific, because the sensitivities to acetylcholine and oxytocin were not influenced in either case. Pargyline (10(-5) M), an inhibitor of monoamine oxidase, did not affect the contractile responses to 5-HT, acetylcholine and oxytocin of uterus from ovariectomized rats. The monoamine oxidase activities in 100,000 X g precipitates and supernatants of homogenates for uteri from ovariectomized rats were either increased or unchanged by administration of estradiol. The contractile response to 5-HT of the uterus of untreated ovariectomized rats was not affected by chlorimipramine at 10(-6) M, a concentration that inhibits 5-HT uptake. Administration of estradiol increased significantly the number of [3H]spiroperidol binding sites (5-HT receptors) from 0.56 +/- 0.04 to 1.23 +/- 0.11 pmol/mg of protein, but did not change the apparent affinity of 5-HT receptors. Administration of estradiol did not change the dissociation constant or number of binding sites for [3H]quinuclidinyl benzilate (muscarinic acetylcholine receptors) significantly. These results indicate that the specific increase in sensitivity to 5-HT on administration of estradiol is due to change in the number of 5-HT receptors, but not to change in 5-HT uptake or in metabolic degradation of 5-HT.

Animals↗
PubMed1983

Increase of serotonin receptors in rat uterus induced by estradiol.

[3H]Spiroperidol was used to label uterine membrane-binding sites that have the characteristics expected of serotonergic receptors. The characteristics of specific [3H]spiroperidol binding to the uterine membrane of 17 beta-estradiol-3-benzoate-treated ovariectomized rats were studied. The specific [3H]spiroperidol binding was rapid and reversible, and the half-maximal saturation, taken as the apparent dissociation constant (KD) for [3H]spiroperidol, was 5.16 +/- 0.24 (n = 12) nM [3H]spiroperidol. Scatchard plots of saturation curves of the specific [3H]spiroperidol binding were convex and the Hill coefficient was 2.06 +/- 0.11 (n = 12). Cinanserin, mianserin, metergoline (which are serotonergic antagonists), and serotonin (5-HT) inhibited the [3H]spiroperidol binding with apparent Ki values of 21.2, 14.1, 14.1, and 176.5 microM, respectively. Concentrations of 1 mM sulpiride (a dopaminergic antagonist) and dopamine reduced [3H]spiroperidol binding only 26 and 23%, respectively. 1 mM GTP reduced the potency of 5-HT (10(-6) - 10(-3) M) to displace bound [3H]spiroperidol. The uterine membranes were treated with various enzymes and protein-modifying reagents, and binding studies on the treated uterine membranes showed that protein(s), phospholipids, and N-acetyl-neuraminic acid in uterine membranes were important as specific binding sites of [3H]spiroperidol. Measurement of the specific binding of [3H]spiroperidol to uterine membranes from untreated and estradiol-treated ovariectomized rats showed that estradiol significantly increased the number of specific binding sites of [3H]spiroperidol, but did not change the apparent affinity of specific [3H]spiroperidol binding. Estradiol also did not change the dissociation constant or the number of binding sites for [3H]3-quinuclidinyl benzilate, which binds to muscarinic acetylcholine receptors. These findings suggest that [3H]spiroperidol mainly binds to 5-HT receptors in the uterine membrane of estradiol-treated ovariectomized rats. The finding that administration of estradiol significantly increased the number of [3H]spiroperidol-binding sites is consistent with the specific increase in the contractile response to 5-HT observed in isolated uterus from ovariectomized rats treated with estradiol.

Animals↗
PubMed1983

Streptozotocin-induced elevation of pancreatic taurine content and suppressive effect of taurine on insulin secretion.

The role of taurine in pancreatic insulin secretion was studied. The administration of the pancreato-toxic streptozotocin (STZ) induced a significant increase of pancreatic taurine content in ddY and CD-1 strains of mice in addition to a remarkable hyperglycemia which resulted from significant damage to the beta-cells of this organ. The increase in pancreatic taurine content was invariably observed under both the transient and the continuous hyperglycemic conditions induced by STZ. It was also shown by analysing lyophilized pancreatic sections that this elevation of taurine content in the pancreas induced by STZ was due to the rise of taurine level in the exocrine tissues, whereas that in the islets of Langerhans was not affected by STZ. On the other hand, the in vitro addition of taurine (1-10 mM) significantly suppressed the glucose-stimulated and Ca2+-dependent secretion of insulin (IRI) from the isolated islets of Langerhans without affecting the Ca2+-independent secretion of this hormone. Considering the results described above, it seems possible that the action site of taurine may be at the exterior of islet cells, perhaps at the cellular membranes of the islets of Langerhans. The present results suggest that pancreatic taurine may play a significant physiological role in the regulation of insulin secretion from the islets of Langerhans and of the serum level of glucose.

Animals↗