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Biomedical subjects

Y Sako

Publications and source records attributed to Y Sako.

At least 73 records · Page 4Linked to original sources
PubMed1996

Rhodothermus obamensis sp. nov., a modern lineage of extremely thermophilic marine bacteria.

A novel extremely thermophilic bacterium was isolated from a shallow marine hydrothermal vent environment (depth, 22 m) in Tachibana Bay, Nagasaki Prefecture, Japan. The cells of this organism were gram-negative rods. Growth occurred at temperatures between 50 and 85 degrees C (optimum temperature, 80 degrees C; doubling time at optimum temperature, 90 min), at pH 5.5 and 9.0 (optimum pH, 7.0), and in the presence of 1 and 5% NaCl (optimum NaCl concentration, 3%). The new isolate was an aerobic heterotroph which utilized the following compounds as sole energy and carbon sources: yeast extract, peptone, starch, casein, Casamino Acids, a variety of sugars, some carboxylic acids, and amino acids. As determined by a sequence analysis of the 16S rRNA, the new isolate belongs to the genus Rhodothermus and represents a modern lineage of extreme thermophiles within the domain Bacteria. On the basis of the physiological and molecular properties of the new isolate, we describe a new species, Rhodothermus obamensis. The type strain of R. obamensis is strain OKD7 (= JCM 9785).

Base Sequence↗
PubMed1995

Expression of a 32 kilodalton Theileria sergenti piroplasm surface protein by recombinant baculoviruses.

Previous studies detected a single amino acid substitution (Ala196 to Gly196) between cDNA clones encoding a 32 kDa antigen (p32) of Theileria sergenti (Chitose stock) obtained from a persistently infected calf. In this study, 2 different recombinant baculoviruses (pAc/p32-Ala196 and pAc/p32-Gly196) were constructed for the expression of p32. Molecular masses of the polypeptides produced in Spodoptera frugiperda cells infected with the recombinant baculoviruses were the same as that of authentic p32. pAc/p32-Ala196 produced additional polypeptides, with molecular masses higher than 32 kDa, which resulted from differential N-glycosylation as revealed by endo N-glycosidase treatment. The results indicate that a single amino acid substitution may lead to a conformational change in p32 which affected post-translational modification of recombinant products.

Alanine↗
PubMed1995

Metabolism of oxidized glycated low-density lipoprotein in cultured bovine aortic endothelial cells.

The serum concentration of glycated low-density lipoprotein (gLDL) is increased in individuals with diabetes mellitus, which may be a contributing factor to the increased incidence of atherosclerosis in this population. Given the importance of oxidized LDL (oLDL) in atherosclerosis and that vascular endothelial cells express receptors for oLDL, oxidized glycated LDL (ogLDL) was prepared in vitro and its binding and degradation by cultured bovine aortic endothelial cells were examined. Glycation of native LDL (nLDL) isolated from normal human subjects was performed by incubation with 20 mM glucose at 37 degrees C for 3 days, and ogLDL was prepared by oxidation of gLDL with 1 microM CuSO4 at 37 degrees C for 12 hours. The electrophoretic mobility and thiobarbituric acid reactive substance (TBARS) value of ogLDL were greater than those of nLDL and gLDL. Both binding and degradation of ogLDL by cultured endothelial cells also were significantly greater than for nLDL and gLDL. Degradation of nLDL by endothelial cells was completely inhibited by ogLDL, whereas degradation of acetylated LDL was not inhibited by nLDL or ogLDL. Thus, the binding and degradation of ogLDL by endothelial cells do not appear to be mediated by the scavenger receptor. Although the exact mechanism is not clear, it appears that vascular endothelial cells may play a protective role against atherosclerosis by removing potential atherogenic lipoproteins.

Animals↗
PubMed1995

Barriers for lateral diffusion of transferrin receptor in the plasma membrane as characterized by receptor dragging by laser tweezers: fence versus tether.

Our previous results indicated that the plasma membrane of cultured normal rat kidney fibroblastic cell is compartmentalized for diffusion of receptor molecules, and that long-range diffusion is the result of successive intercompartmental jumps (Sako, Y. and Kusumi, A. 1994. J. Cell Biol. 125:1251-1264). In the present study, we characterized the properties of intercompartmental boundaries by tagging transferrin receptor (TR) with either 210-nm-phi latex or 40-nm-phi colloidal gold particles, and by dragging the particle-TR complexes laterally along the plasma membrane using laser tweezers. Approximately 90% of the TR-particle complexes showed confined-type diffusion with a microscopic diffusion coefficient (Dmicro) of approximately 10(-9) cm2/s and could be dragged past the intercompartmental boundaries in their path by laser tweezers at a trapping force of 0.25 pN for gold-tagged TR and 0.8 pN for latex-tagged TR. At lower dragging forces between 0.05 and 0.1 pN, particle-TR complexes tended to escape from the laser trap at the boundaries, and such escape occurred in both the forward and backward directions of dragging. The average distance dragged was half of the confined distance of TR, which further indicates that particle-TR complexes escape at the compartment boundaries. Since variation in the particle size (40 and 210 nm, the particles are on the extracellular surface of the plasma membrane) hardly affects the diffusion rate and behavior of the particle-TR complexes at the compartment boundaries, and since treatment with cytochalasin D or vinblastin affects the movements of TR (Sako and Kusumi as cited above), argument has been advanced that the boundaries are present in the cytoplasmic domain. Rebound of the particle-TR complexes when they escape from the laser tweezers at the compartment boundaries suggests that the boundaries are elastic structures. These results are consistent with the proposal that the compartment boundaries consist of membrane skeleton or a membrane-associated part of the cytoskeleton (membrane skeleton fence model). Approximately 10% of TR exhibited slower diffusion (Dmicro approximately 10(-10)-10(-11) cm2/s) and binding to elastic structures.

Animals↗
PubMed1995

Impaired feedback inhibition of insulin secretion by hyperinsulinemia in patients with insulinoma.

By means of the euglycemic three step hyperinsulinemic clamp technique, suppression of endogenous C-peptide secretion by exogenous insulin infusion was evaluated in patients with insulinoma (n = 8) and healthy controls (n = 20). Euglycemic hyperinsulinemic clamp studies were performed with an artificial pancreas (STG-22 NIKKISO, Tokyo, Japan). Insulin (Actrapid human insulin) was infused at the rate of 1.12, 3, and 10 mU/kg/min. Plasma glucose levels were clamped at 80 mg/dl, and high insulin levels were maintained in all subjects (833 +/- 78 microU/ml at the rate of 10 mU/kg/min insulin infusion). During the clamp studies, plasma C-peptide levels in normal subjects declined from 2.0 +/- 0.2 to 0.9 +/- 0.2 ng/ml, indicating suppression of endogenous insulin secretion by exogenous insulin infusion. In patients with insulinoma, plasma C-peptide levels were 3.1 +/- 1.6 ng/ml in the basal state, and were not suppressed even during exogenous hyperinsulinemia. We concluded that the feedback inhibition of insulin secretion by exogenous insulin infusion is attenuated in patients with insulinoma, and that the hyperinsulinemic clamp technique may be a useful method for the diagnosis of insulinoma.

Adult↗
PubMed1995

Secretion of insulin and glucagon by the perfused pancreas of genetically obese (fa/fa) Zucker rats and its alteration with aging.

To evaluate the sequential changes in secretion of insulin and glucagon by the pancreas of Zucker fa/fa rats, we examined the secretion of these peptides by the perfused pancreas of the rats and by that of their lean littermates aged 9, 18, and 54 wks. Obese rats weighted significantly more than lean rats at all ages and had increased plasma insulin except for those at 54 wks of age. Isolated pancreas of obese rats at 9 wks showed greater insulin secretion response to glucose and arginine than that of lean rats at the same age. Insulin secretion response to arginine from pancreas of obese rats at 18 wks was also greater than that from pancreas of lean rats at 18 wks. Increased glucose concentration in the perfusion medium caused less suppression in obese rats than in lean rats. 10 mM arginine stimulation resulted in a higher secretion response in lean rats than in obese rats at 18 and 54 wks. Impairment of glucagon secretion was observed even at 54 wks of age, when the obese rats no longer had significantly increased plasma insulin. This suggested that abnormal glucagon secretion was due not only to hyperinsulinemia, but also to a possible defect in the secretory mechanism.

Aging↗
PubMed1994

Sulfamethizole capsule method. A new method for assessing gastric emptying of solids.

We have developed a new method that is capable of assessing gastric emptying in humans. This method is based on the rapid absorption of sulfamethizole in the upper small intestine. Sulfamethizole capsules are gelatin capsules that are filled with a solid composed of egg albumin and sulfamethizole. After subjects ingested of 15 capsules with ham and bread, blood concentrations of sulfamethizole were measured and the areas under the sulfamethizole concentration-time curve (AUC) were calculated as an index of gastric emptying. After ingestion of 99mTc-labeled sulfamethizole capsules, there was a statistically significant correlation between the percentage of radioactivity remaining in the stomach at 120 min and AUC for 120 min (r = -0.82, P < 0.01). This method yielded a reliable value for gastric emptying of a solid meal as estimated by AUC. This method can be considered safe and is easily applicable to human subjects for assessment of gastric emptying.

Adult↗
PubMed1994

Insulin treatment improves relative hypersecretion of amylin to insulin in rats with non-insulin-dependent diabetes mellitus induced by neonatal streptozocin injection.

The dissociated release of insulin and amylin in the hyperglycemic state has been reported. This relative hypersecretion of amylin is thought to provide an important insight into how amylin aggregates to form islet amyloid deposits in non-insulin-dependent diabetes mellitus (NIDDM). The aim of the present study was to characterize the alterations of amylin hypersecretion in NIDDM with exacerbation or amelioration of diabetic control. For this purpose, neonatally streptozocin (nSTZ) diabetic rats were treated with dexamethasone (0.25 mg/kg) or Lente insulin (3 to 5 U/kg) daily for 14 days, and responses of amylin and insulin to 16.7 mmol/L glucose or 10 mmol/L arginine were evaluated in vitro using an isolated perfused pancreas system. nSTZ rats exhibited moderate elevations of plasma glucose compared with normal rats. In the isolated perfused pancreas, the molar ratio of secreted amylin to insulin in response to 16.7 mmol/L glucose by nSTZ pancreas (1.8% +/- 0.2%) was significantly greater than that of normal rat pancreas (1.2% +/- 0.1%). Plasma glucose levels in nSTZ rats (7.3 +/- 0.4 mmol/L) increased with dexamethasone treatment (17.8 +/- 1.1 mmol/L, P < .005) and decreased with insulin treatment (5.8 +/- 0.4 mmol/L, P < .05). The secreted amylin to insulin ratio in dexamethasone-treated nSTZ rats was significantly greater than that of the controls (P < .05). Moreover, insulin-treated nSTZ rats exhibited decreased amylin to insulin molar ratios compared with saline-treated nSTZ rats (P < .05), which had the same levels as normal rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗
PubMed1994

Compartmentalized structure of the plasma membrane for receptor movements as revealed by a nanometer-level motion analysis.

Movements of transferrin and alpha 2-macroglobulin receptor molecules in the plasma membrane of cultured normal rat kidney (NRK) fibroblastic cells were investigated by video-enhanced contrast optical microscopy with 1.8 nm spatial precision and 33 ms temporal resolution by labeling the receptors with the ligand-coated nanometer-sized colloidal gold particles. For both receptor species, most of the movement trajectories are of the confined diffusion type, within domains of approximately 0.25 microns2 (500-700 nm in diagonal length). Movement within the domains is random with a diffusion coefficient approximately 10(-9) cm2/s, which is consistent with that expected for free Brownian diffusion of proteins in the plasma membrane. The receptor molecules move from one domain to one of the adjacent domains at an average frequency of 0.034 s-1 (the residence time within a domain approximately 29 s), indicating that the plasma membrane is compartmentalized for diffusion of membrane receptors and that long-range diffusion is the result of successive intercompartmental jumps. The macroscopic diffusion coefficients for these two receptor molecules calculated on the basis of the compartment size and the intercompartmental jump rate are approximately 2.4 x 10(-11) cm2/s, which is consistent with those determined by averaging the long-term movements of many particles. Partial destruction of the cytoskeleton decreased the confined diffusion mode, increased the simple diffusion mode, and induced the directed diffusion (transport) mode. These results suggest that the boundaries between compartments are made of dynamically fluctuating membrane skeletons (membrane-skeleton fence model).

Animals↗
PubMed1994

Adult T-cell leukaemia with various abnormalities in endocrine and metabolic systems.

Adult T-cell leukaemia (ATL) is a unique type of T-cell malignancy closely associated with human T-cell leukaemia virus-1 (HTLV-1). Despite frequent descriptions of hypercalcaemia, cases accompanied by diabetes insipidus or syndrome of inappropriate secretion of anti-diuretic hormone (SIADH) in ATL patients have rarely been reported. We present an unusual case of ATL with various abnormalities in his endocrine and metabolic systems involving anterior pituitary function, thyroid function, lipid metabolism and Ca metabolism. Some of these abnormalities were considered to arise from infiltration or leukaemic cells into systemic organs after elimination of the above symptoms. Clinical and haematological data showing improvement following chemotherapy are also presented.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1993

Plasma homocysteine concentrations in Japanese patients with non-insulin-dependent diabetes mellitus: effect of parenteral methylcobalamin treatment.

It has been postulated that the accumulation of homocysteine in plasma may induce arteriosclerosis. In order to explore the possible contribution of homocysteine to the occurrence of macroangiopathy in patients with non-insulin-dependent diabetes mellitus, the concentrations of total homocysteine in plasma were determined in 52 diabetic patients with clinical macroangiopathy, 84 diabetic patients without macroangiopathy, and 57 non-diabetic control subjects. The levels of total homocysteine in plasma were significantly higher in diabetic patients with macroangiopathy (10.8 +/- 3.8 nmol/ml) than in those without macroangiopathy (8.3 +/- 3.1 mmol/ml, P < 0.001) or non-diabetic subjects (7.5 +/- 2.1 nmol/ml, P < 0.001). Among all diabetic patients, multiple logistic regression analysis after adjustment for age, sex, and systolic blood pressure revealed that high levels of plasma homocysteine were significantly associated with the presence of diabetic macroangiopathy (P = 0.01). By an intramuscular injection of 1000 micrograms methylcobalamin daily for 3 weeks, the plasma levels of homocysteine in 10 diabetic patients were significantly decreased (14.7 +/- 7.5 vs. 10.2 +/- 6.0 nmol/ml, P < 0.01). Our results suggest that plasma homocysteine levels could be one of a number of independent risk factors for macroangiopathy in patients with diabetes mellitus and that they can be reduced by parenteral treatment with methylcobalamin.

Adult↗
PubMed1993

Confined lateral diffusion of membrane receptors as studied by single particle tracking (nanovid microscopy). Effects of calcium-induced differentiation in cultured epithelial cells.

The movements of E-cadherin, epidermal growth factor receptor, and transferrin receptor in the plasma membrane of a cultured mouse keratinocyte cell line were studied using both single particle tracking (SPT; nanovid microscopy) and fluorescence photobleaching recovery (FPR). In the SPT technique, the receptor molecules are labeled with 40 nm-phi colloidal gold particles, and their movements are followed by video-enhanced differential interference contrast microscopy at a temporal resolution of 33 ms and at a nanometer-level spatial precision. The trajectories of the receptor molecules obtained by SPT were analyzed by developing a method that is based on the plot of the mean-square displacement against time. Four characteristic types of motion were observed: (a) stationary mode, in which the microscopic diffusion coefficient is less than 4.6 x 10(-12) cm2/s; (b) simple Brownian diffusion mode; (c) directed diffusion mode, in which unidirectional movements are superimposed on random motion; and (d) confined diffusion mode, in which particles undergoing Brownian diffusion (microscopic diffusion coefficient between 4.6 x 10(-12) and 1 x 10(-9) cm2/s) are confined within a limited area, probably by the membrane-associated cytoskeleton network. Comparison of these data obtained by SPT with those obtained by FPR suggests that the plasma membrane is compartmentalized into many small domains 300-600 nm in diameter (0.04-0.24 microns2 in area), in which receptor molecules are confined in the time scale of 3-30 s, and that the long-range diffusion observed by FPR can occur by successive movements of the receptors to adjacent compartments. Calcium-induced differentiation decreases the sum of the percentages of molecules in the directed diffusion and the stationary modes outside of the cell-cell contact regions on the cell surface (which is proposed to be the percentage of E-cadherin bound to the cytoskeleton/membrane-skeleton), from approximately 60% to 8% (low- and high-calcium mediums, respectively).

Animals↗
PubMed1993

Fluorescence lifetime imaging microscopy (flimscopy). Methodology development and application to studies of endosome fusion in single cells.

A new method of fluorescence microscopy for cell imaging has been developed that takes advantage of the spatial variations of fluorescence lifetimes in single cells as a source of image contrast, and thus it is named "fluorescence lifetime imaging microscopy (flimscopy)". Since time-resolved fluorescence measurements are sensitive to molecular dynamics and interactions, flimscopy allows the molecular information to be visualized in single cells. In flimscopy measurements, several (nanosecond) time-resolved fluorescence images of a sample are obtained at various delay times after pulsed laser excitation of the microscope's entire field of view. Lifetimes are calculated pixel-by-pixel from these time-resolved images, and the spatial variations of the lifetimes are then displayed in a pseudocolor format (flimscopy image). The total data acquisition time needed to obtain a flimscopy image with the diffraction-limited spatial resolution (approximately 250 nm) is decreased to just approximately 30 s for approximately 300 fluorescent molecules/micron2. This was achieved by developing a high-frequency (400 kHz) nanosecond-gating (9 ns full width at half height)-signal accumulation system. This technique allows the extent of resonance energy transfer to be visualized in single living cells, and is free from the errors due to variations in path length, light scattering, and the number of fluorophores that necessitate complex corrections in steady-state microfluorometry and fluorescence ratio imaging microscopy. Flimscopy was applied here to observe the extent of fusion of individual endosomes in single cells. Results revealed the occurrence of extensive fusion between primary endocytic vesicles and/or sorting endosomes, thereby raising the possibility that the biogenesis of sorting endosomes involves multiple fusions of primary endocytic vesicles.

Animals↗
PubMed1992

Diazoxide infusion at excess but not at basal hyperglycemia enhances beta-cell sensitivity to glucose in vitro in neonatally streptozotocin-diabetic rats.

The influence of chronic and moderate hyperglycemia vis-à-vis a 48-hour further elevation of blood glucose on beta-cell sensitivity to glucose was compared in an animal model of non-insulin-dependent diabetes. Neonatally streptozotocin-diabetic (n-STZ) rats infused with saline for 48 hours displayed moderate nonfasting hyperglycemia (mean, 11.5 +/- 1.5 mmol/L/48 h) and plasma insulin levels similar to those seen in normoglycemic, nondiabetic rats. In perfused pancreas, the insulin response to 27 mmol/L glucose was severely reduced to 1.60 +/- 0.45 pmol/min, ie, approximately 15% of the response in nondiabetic rats. A continuous infusion of diazoxide (5 mg/kg/h), which normally blocks glucose-induced insulin secretion, did not affect glucose and insulin levels in vivo, nor did it significantly affect the insulin response to glucose in vitro. In other experiments, "basal" hyperglycemia in n-STZ rats was doubled by glucose infusions for 48 hours to reach a mean of 23.8 +/- 0.6 mmol/L. Plasma insulin increased 3.2-fold. The in vitro insulin response to 27 mmol/L glucose was totally abolished, and the pancreatic insulin content was decreased by 81% relative to the content after saline. Addition of a diazoxide infusion inhibited the increase in plasma insulin by 93%. After the combined glucose and diazoxide infusion, the subsequent in vitro response to 27 mmol/L glucose was dramatically enhanced to 9.55 +/- 3.25 pmol/min, ie, the response was sixfold higher than after saline alone. This aftereffect of the diazoxide infusion was not significantly altered by an insulin infusion (2 U/d) added to the hyperglycemia plus diazoxide protocol to compensate for the insulin-lowering effect of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗