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Biomedical subjects

I Miwa

Publications and source records attributed to I Miwa.

At least 73 records · Page 4Linked to original sources
PubMed1990

High-yield purification of glucokinase from rat liver.

A rapid and reliable method for the purification of rat liver glucokinase was developed. The procedure consists of DEAE-cellulose ion-exchange chromatography, Phenyl-Sepharose hydrophobic interaction chromatography, DEAE-Affi Gel Blue dye-ligand chromatography, and duplicate steps of glucosamine-Sepharose affinity chromatography. Glucokinase was purified to a specific activity of 290 units/mg protein in a yield of 55% in 6 days. The final enzyme preparations were completely homogeneous in most experiments as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The estimated molecular weight (51,000) and sigmoidal saturation function for glucose of purified glucokinase were in good agreement with published data.

Animals↗
PubMed1990

Effects of novel hydantoin derivatives with aldose reductase inhibiting activity on galactose-induced cataract in rats.

Effects of novel aldose reductase inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), on galactose-induced cataract formation in rats were investigated. Rats fed a 30% galactose diet developed lenticular opacity in the peripheral region by the 6th day of galactose feeding and showed gradual progression of opacity from the equator to the center of lenses. Histological study on the 15th day showed apparent lens fiber swelling and vacuolation predominantly in the equatorial and anterior cortical regions. Biochemical changes such as accumulation of galactitol, depletion of myo-inositol and decrease in glutathione (GSH) content in lenses preceded the appearance of opacity. Remarkable increase in NADPH content and decrease in NADP+ content, in addition to elevation of the ratio of Na+/K+, in lenses were also observed on the 15th day. Both M16209 and M16287 (10, 30 and 100 mg/kg/day, p.o.) dose-dependently ameliorated these morphological and biochemical changes except that restoration of myo-inositol content was incomplete. These results indicate that M16209 and M16287 can prevent galactose-induced cataract formation through amelioration of metabolic disorders and thus have high potential for clinical use in the treatment of some diabetic complications.

Aldehyde Reductase↗
PubMed1990

Participation of glucokinase inactivation in inhibition of glucose-induced insulin secretion by 2-cyclohexen-1-one.

We assessed our speculation that 2-cyclohexen-1-one (CHX) impairs glucose-induced insulin secretion through inactivation of glucokinase. Treatment of pancreatic islets with CHX at concentrations (0-5 mM) that caused a dose-dependent inactivation of glucokinase activity similarly inhibited glucose-induced insulin secretion. Another glucose-phosphorylating enzyme (hexokinase) in pancreatic islets was little affected by CHX. CHX-induced inactivation of glucokinase was blocked by the presence of its substrates (glucose and mannose) and an inhibitor (N-acetylglucosamine), all of which also protected against the inhibitory effect of the drug on glucose-induced insulin secretion. CHX also impaired insulin secretion induced by D-glyceraldehyde and dimethyl succinate, which are believed to stimulate the release of the hormone by being directly oxidized by glyceraldehyde-3-phosphate dehydrogenase, by entering the midstream of the glycolytic pathway as glyceraldehyde 3-phosphate, or by entering the tricarboxylic acid cycle in mitochondria after intracellular hydrolysis. The inhibitory effect of CHX on glucose-induced insulin secretion, however, was far more marked than that on insulin secretion evoked by D-glyceraldehyde and dimethyl succinate at any CHX concentrations used. Our study revealed that the inhibitory action of CHX on glucose-induced insulin secretion is exerted mainly, but not solely, through inactivation of glucokinase. This conclusion supports the view that glucokinase is a key enzyme in the recognition of glucose as an insulin secretagogue in pancreatic islets.

Animals↗
PubMed1990

Evidence for the presence of rat liver glucokinase in the nucleus as well as in the cytoplasm.

Subcellular distribution of glucokinase was studied in rat liver. With an immunohistochemical procedure, glucokinase immunoreactivity was clearly shown in the nucleus of parenchymal cells of rat liver, but faintly in the cytoplasm. Nuclei, cytosol (extranuclear fraction in the strict sense), and homogenate prepared in nonaqueous medium, i.e. glycerol, were analyzed for glucokinase by both immunoblotting and activity measurement. Such analyses demonstrated that glucokinase concentration was far higher in the nuclei than in the cytosol when compared on the basis of total protein content and that total glucokinase activity in the cytosolic fraction was about 1.8 times that in the nuclear fraction. These results indicate that hepatocyte glucokinase is present in the nucleus as well as in the cytoplasm in contradiction to the widespread belief of its exclusive localization in the cytoplasm.

Animals↗
PubMed1989

Circadian rhythm of photoaccumulation in Paramecium bursaria.

Populations of Paramecium bursaria cells display a circadian rhythm of photoaccumulation. Both Chlorella-containing cells and Chlorella-free cells exhibit this rhythm. Several other species of Paramecium do not express rhythmic photoaccumulation when tested under the same conditions. In P. bursaria, photoaccumulation rhythms persist in continuous conditions (constant temperature and either continuous light or continuous darkness). The period of this rhythm is "temperature-compensated," with a Q10 of 1.10-1.12. The rhythm can be reset by pulses of light or darkness in a phase-dependent manner. Therefore, an endogenous circadian oscillator controls photoaccumulation behavior in P. bursaria.

Animals↗
PubMed1989

Improvement of nerve conduction velocity in mutant diabetic mice by aldose reductase inhibitor without affecting nerve myo-inositol content.

The sciatic motor nerve conduction velocity of mutant diabetic C57BL/Ks mice was significantly improved from 30.0 +/- 1.4 to 38.0 +/- 4.6 m/s by treatment with the aldose reductase inhibitor 1-[(beta-naphthyl)sulfonyl]hydantoin (30 mg/kg/d) for 2 weeks. The treatment, however, did not cause any significant change in myo-inositol concentration in the sciatic nerve. The results indicate that the ameliorating effect of the aldose reductase inhibitor on nerve conduction velocity in mutant diabetic mice is not due to alteration of myo-inositol content in the nerve.

Aldehyde Reductase↗
PubMed1988

Analysis of sorbitol, galactitol, and myo-inositol in lens and sciatic nerve by high-performance liquid chromatography.

Accumulation of sorbitol or galactitol and depletion of myo-inositol in hyperglycemic conditions such as diabetes and galactosemia involve the activity of aldose reductase and are implicated in hyperglycemia-induced complications such as cataract and neuropathy. A high-performance liquid chromatographic method has been developed for the measurement of polyols in the lens and sciatic nerve of rats. This method comprises polyol extraction from tissues, lyophilization of extracts, derivatization of polyols by the reaction with phenylisocyanate, and HPLC of derivatives with detection at 240 nm. The time needed for each run is less than 25 min, which allows the testing of a large number of samples per day. Sensitivity is very high: as low as 0.5 nmol each of sorbitol, galactitol, and myo-inositol in lyophilized extracts of tissues can be determined. The present method offers a reliable tool to evaluate the in vivo activities of aldose reductase and its inhibitors.

Animals↗
PubMed1988

Asymmetric transport of D-glucose anomers across the human erythrocyte membrane.

The anomeric preference in the influx and efflux of D-glucose across the human erythrocyte membrane was studied. beta-D-Glucose was transported 1.5 times faster than alpha-D-glucose into the cells, when washed cells were incubated at 20 degrees C in medium containing either alpha- or beta-D-glucose (100 mM). On the other hand, no difference between half-times of efflux of the two anomers was distinguishable. The result demonstrates the presence of influx-efflux asymmetry in anomeric preference in D-glucose transport across the human erythrocyte membrane, and is consistent with the view (Barnett et al., Biochem. J. 145, 417-429, 1975) that the C-1 hydroxyl group of D-glucose interacts with the D-glucose transport protein only in the influx, but not in the efflux.

Erythrocyte Membrane↗
PubMed1987

Development of potent aldose reductase inhibitors having a hydantoin structure.

Seventeen hydantoin derivatives were tested as inhibitors of aldose reductase, an enzyme believed to participate in the initiation of diabetic complications. Nine compounds with high inhibitory activities (IC50 values against purified rat lens aldose reductase less than or equal to 1.06 X 10(-6)M) were tested further for their abilities to prevent sorbitol accumulation induced by exposure of excised rat lens and sciatic nerve to a high glucose concentration (50 mM). Seven active compounds among them inhibited sorbitol accumulation by about 50% or more at a concentration of 10(-5)M. These seven compounds were given orally to streptozotocin-induced diabetic rats at a dose of 50 mg/kg/day and were assessed for their abilities to prevent both sorbitol accumulation in two tissues (lens and sciatic nerve) and myo-inositol depletion in the sciatic nerve. 1-[(2,4,5-Trichlorophenyl)sulfonyl]hydantoin, 1-[(2,5-dichlorophenyl)sulfonyl]hydantoin, and 1-[(beta-naphthyl)sulfonyl]hydantoin were found to be the most effective: they inhibited sorbitol accumulation in the sciatic nerve completely and that in the lens by more than 92%. It is conceivable from this study that the three compounds are promising for further investigation targeted to the treatment of diabetic complications.

Aldehyde Reductase↗
PubMed1987

Anomeric specificity of glucose effect on cAMP, fructose 1,6-bisphosphatase, and trehalase in yeast.

The addition of beta-D-glucose (final concentration, 50 mM) to a cell suspension of Saccharomyces cerevisiae in stationary phase caused a rapid 4-fold increase in the concentration of cAMP, while a 2-fold increase of cAMP was observed by the addition of alpha-D-glucose. beta -D-Glucose was also more effective than alpha-D-glucose in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase. These results, taken together with the previous report that alpha-D-glucose is transported more rapidly than beta-D-glucose in Saccharomyces cerevisiae, do not support the view currently proposed by some investigators that cotransport of D-glucose with protons causes the depolarization of the cell membrane, resulting in the activation of adenylate cyclase. The present data, however, provides supporting evidence for the view that cAMP-dependent protein kinase is implicated in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase.

Cyclic AMP↗
PubMed1987

Circadian rhythmicity within single cells of Paramecium bursaria.

Cell populations of Paramecium bursaria show mating reactivity in the light period, but not in the dark period, when exposed to a light-dark cycle (LD 12:12). After they are transferred to constant-light (LL) conditions (1,000 lux), they continue to show a circadian rhythm of mating reactivity. The rhythm gradually dampens in LL so that mating reactivity in populations becomes arrhythmic in LL within 2 weeks. We wanted to know whether the arrhythmicity of this population was due to the absence of circadian rhythmicity within each individual cell, or merely due to asynchrony of a population of individually rhythmic cells. Therefore, single cells were isolated randomly from an arrhythmic population that had been in LL for a long time. Then the mating reactivity of these single cells was individually tested every 3 hr for 2 days. Each single cell showed a circadian mating rhythm in LL. This shows that the disappearance of the mating rhythm in cell populations under LL is not caused by disappearance of circadian rhythmicity within individual cells, but is due to desynchronization among cells in a population. When an arrhythmic population in LL is darkened for 9 hr, the mating reactivity rhythm of the cell population reappears. This occurs by resynchronization of the rhythms among individual cells, as can be shown by exposing single cells to pulses of 9 hr of darkness. This dark treatment causes phase shifts of single-cell rhythms, and a phase response curve is obtained for this stimulus. This phase-shifting behavior explains the efficacy of 9-hr dark pulses in restoring the population's rhythm.

Animals↗
PubMed1986

Glucose transport into human erythrocytes treated with phospholipase A2 or C.

Phospholipase A2 induced crenation of human erythrocytes and decreased glucose transport activity (influx rate) by 40% when 51% of phosphatidylcholine (PC) in the membrane was hydrolyzed. On the other hand, phospholipase C induced invagination of the cells and negligibly affected the glucose transport in the case of 21% hydrolysis of the PC. By altering the pH of the medium for suspending cells treated with phospholipase A2 from 7.4 to 6.0, cell shape was changed from clear crenation to slight invagination, but glucose transport activity was not affected. Cells that were treated with phospholipase A2 and then washed with albumin to remove free fatty acids produced in the cell membrane showed an almost normal cell shape and slightly higher glucose transport activity than did untreated cells. The ratios of beta-D-glucose transport rate to alpha-D-glucose transport rate in untreated cells, cells treated with phospholipase A2 and cells treated with phospholipase C were 1.13, 1.04, and 1.20, respectively. These results demonstrate that the drastic morphological change (invagination or crenation) induced by the treatment with phospholipases bears no clear relationship to the activity of glucose transport and suggest that the increase in the volume of the outer half of the lipid bilayer might reduce the rate of glucose transport across the human erythrocyte membrane and change the anomeric preference of glucose transport.

Biological Transport↗
PubMed1986

Effect of exogenous lipids incorporated into the membrane of human erythrocytes on its glucose transport activity.

Addition of a phosphatidylcholine (dilinoleoyl), lysophosphatidylcholine (palmitoyl), saturated or unsaturated long-chain fatty acid (stearic or oleic) into human erythrocyte suspension caused both dose-dependent incorporation of the lipid into the membrane and inhibition of the glucose transport across the membrane. Loading to or partial removal of cholesterol from the membrane increased or decreased the transport rate, respectively. There was no correlation between the changes in the transport activity and those in cell shape caused by such alterations in the membrane lipid composition.

Blood Glucose↗