892 research outputs found
Structure diversity in three forest types of north-eastern Thailand (Sakaerat Reserve, Pak Tong Chai)
The aim of the present study is to provide a basic knowledge in view of a better understanding of the global structure of threetropical forests at the Sakaerat Environmental Research Station (Pak Tong Chai district, Northeastern Thailand): a drydipterocarp forest (DDF), a dry evergreen forest (DEF) and an intermediate stage (DDFwf), characterized by the absence offire since 29 years in a pyro-climax. These forest ecosystems were contrasted by the composition and floristic structure, thebasal area and the tree density. The species richness increases with the passage from the DDF, the most open environment, to the DDFwf, the most densely wooded. By these tree density and basal area, the DDF (602 trees/ha at DBH ³ 5 cm, 14.2 m2/ha) and the DEF (992 trees/ha at DBH ³ 5 cm, 29.0 m2/ha) studied belong to the typical tropical ecosytems of southeast Asia. The man-made fires and anarchic forest exploitations are a danger for the stability of these different ecosystems
Effects of lactisole on pancreatic islet B-cells electrophysiology
Sucralose mimics the effects of glucose upon several variables of pancreatic islet B-cell metabolism and function, including bioelectrical activity. The present study aimed at investigating whether lactisole, which was recently found to act as an antagonist of the sweet taste receptor TIR3 in pancreatic islet B-cells, also opposes the effects of glucose and/or sucralose upon B-cell electrophysiology. A dual effect of lactisole, both inhibitory and stimulatory, was observed upon the electrical activity of mouse pancreatic islet B-cells. The present findings thus document that agents supposed to act specifically on the TIR3 sweet receptor may either mimic or oppose the effect of glucose upon islet B-cell electrical activity
Porin Proteins in Mitochondria from Rat Pancreatic Islet Cells and White Adipocytes
The binding of hexo-/glucokinase and glycerol kinase to mitochondria via the channel forming protein, porin, in pancreatic islet β-cells and adipocytes, was recently proposed to participate in nutritional signaling, glucose sensing, and the control of high-energy phosphate distribution and oxidative phosphorylation. In this study we demonstrate that polyclonal antisera against purified rat liver porin recognize unique proteins in rat pancreatic islets, adipocytes, and RINm5F cells, each with an apparent Mr about 2000 smaller than that of liver porin. Immunoblotting of subcellular fractions, the purity of which has been controlled by the distribution of marker proteins, revealed the mitochondrial localization of the cross-reacting proteins. Their enrichment with a method used for the purification of porin proteins, the characteristic behavior during isoelectric focusing, and the specific binding of rat liver hexokinase and glycerol kinase to phospholipid vesicles containing the purified cross-reacting β-cell or adipocyte proteins strongly suggest their identity with mitochondrial porin. The subtle differences in the apparent Mr and charge heterogeneity raise the possibility of the existence of porin isoforms expressed in a tissue-specific manner. Anti-porin antisera coimmunoprecipitated hexo-/glucokinase from rat insulinoma cell (RINm5F) and adipocyte mitochondria as determined by subsequent immunoblotting of the immunoprecipitates with polyclonal antisera against yeast hexokinase and rat liver glucokinase, respectively. This indicates that some rat pancreatic glucokinase (54 kDa) and liver hexokinase (102 kDa), respectively, is bound to mitochondrial porin. The major portion of the bound fraction is released from mitochondria after treatment with glucose 6-phosphate. Incubation of RINm5F and fat cells with the insulin releasing sulfonylurea drug, glimepiride (20 nM and 5 μM, respectively) for 30 min reduces the amount of hexo-/glucokinase associated with mitochondria and porin to about 50-30%. The reduced kinase binding activity of porin is preserved after isolation of porin from glimepiride-treated cells, reconstitution into phospholipid vesicles and assaying for glucose 6-phosphate inhibitable binding of rat liver hexokinase. The sulfonylurea tolbutamide (20 μM and 5 mM) is significantly less effective. The sulfonylurea-induced inhibition of hexo-/glucokinase binding to mitochondrial porin does not require glucose metabolism or Ca2+ influx into the cells. These data suggest that the sulfonylurea glimepiride, which is thought to inhibit the ATP-regulated K+-channel in β-cells, may have, in addition, an intracellular site of action in pancreatic islet and adipocyte cells at the level of regulation of gluco-/hexokinase binding to mitochondrial porin
Feeding a Protective Hydrolysed Casein Diet to Young Diabetes-prone BB Rats Affects Oxidation of L[U−C14] glutamine in Islets and Peyer's Patches, Reduces Abnormally High Mitotic Activity in Mesenteric Lymph Nodes, Enhances Islet Insulin and Tends to Normalize NO Production
The present studies were undertaken to examine
concomitant diet-induced changes in pancreatic
islets and cells of the gut immune system of
diabetes-prone BB rats in the period before classic
insulitis. Diabetes-prone (BBdp) and control non-diabetes
prone (BBc) BB rats were fed for ~ 17 days
either a mainly plant-based standard laboratory
rodent diet associated with high diabetes frequency,
NIH-07 (NIH) or a protective semipurified diet with
hydrolyzed casein (HC) as the amino acid source. By
about 7 weeks of age, NIH-fed BBdp rats had lower
plasma insulin and insulin/glucose ratio, lower
insulin content of isolated islets, lower basal levels
of NO but higher responsiveness of NO production
to IL-1β in cultured islets, and higher Con A
response and biosynthetic activities in mesenteric
lymphocytes than control rats fed the same diet. In
control rats, the HC diet caused only minor changes
in most variables, except for a decrease in oxidation
of L-[U−C14]glutamine in Peyer's patch (PP) cells and
an increase in protein biosynthesis in mesenteric
lymphocytes. In BBdp rats, however, the HC diet increased plasma insulin concentration, islet insulin/
protein ratio, and tended to normalize the basal
and IL-1β-stimulated NO production by cultured
islets. The HC diet decreased oxidation of L-[U−C14]glutamine in BBdp pancreatic islets, whereas
oxidation of L-[U−C14]glutamine in PP cells was
increased, and the basal [Methyl-H3] thymidine
incorporation in mesenteric lymphocytes was decreased.
These findings are compatible with the
view that alteration of nutrient catabolism in islet
cells as well as key cells of the gut immune system,
particularly changes in mitotic and biosynthetic
activities in mesenteric lymphocytes, as well as
basal and IL-1β stimulated NO production, participate
in the sequence of events leading to autoimmune
diabetes in BB rats. Thus, the protection afforded by feeding a hydrolysed casein-based diet
derives from alterations in both the target islet tissue
and key cells of the gut immune system in this
animal model of type 1 diabetes
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