Tissue Mitochondria Research Articles

Immunoelectron microscopical identification of the uncoupling protein in brown adipose tissue mitochondria

Immunoelectron microscopical identification of the uncoupling protein in brown adipose tissue mitochondria

Acute effects of cold on GDP binding and uncoupling protein concentration in brown adipose tissue mitochondria of genetically obese (ob/ob) mice

Acute effects of cold on GDP binding and uncoupling protein concentration in brown adipose tissue mitochondria of genetically obese (<i>ob/ob</i>) mice

Effect of chemical modification in situ on L-glycerol-3-phosphate dehydrogenase in brown adipose tissue mitochondria.

Mitochondrial L-glycerol-3-phosphate dehydrogenase (E.C. 1.1.99.5.) was studied by chemical modification in situ with different amino acid side chain specific reagents in mitochondria isolated from hamster brown adipose tissue. The SH-modifying reagents have only slight effect on the enzyme activity. The most effective chemicals were tetranitromethane and diazobenzene sulfonic acid. The enzyme activity can be abolished completely by both of them. In the presence of Ca2+ and/or glycerol-3-phosphate inhibition was greater at the same electrophilic reagent concentration. The effect of Ca2+ and glycerol-3-phosphate is nonadditive on inhibition by these reagents.

Teratogenic effects of a lipophilic cationic dye rhodamine 123, alone and in combination with 2-deoxyglucose.

An anti-tumor agent, the cationic dye rhodamine 123 (Rh 123), becomes concentrated in mitochondria of certain tissues and inhibits ATP production. Rh 123 was tested for developmental toxicity by i.p. injection into pregnant CD-1 mice daily on gestation days 7-10 (plug = day 1) at doses up to 15 mg/kg/day. Additional mice were given a 500 mg/kg/day dose of 2-deoxy-glucose (2-DOG), an inhibitor of glycolytic ATP generation, alone or with Rh 123. Controls received saline equimolar to the 2-DOG. Prenatal mortality was increased by Rh 123 in combination with 2-DOG, with values of 40%, 43%, or 41% dead or resorbed at Rh 123 doses of 8, 12, or 15 mg/kg/day, respectively. When given alone, neither test agent was associated with a significant increase in prenatal death. Concurrent treatment with Rh 123 and 2-DOG resulted in significant incidences of gross malformations (17% to 20%) and skeletal malformations (9% to 72%). At the two highest Rh 123 doses (12 and 15 mg/kg/day) given with 2-DOG, significant findings included retarded skeletal ossification and variations (up to 83% and 41%, respectively), as well as decreased fetal weight. According to these results, combinations of rhodamine 123 and 2-deoxyglucose administered to the dam during early organogenesis are developmentally toxic to mice.

Uncoupling protein content of brown adipose tissue mitochondria in fasted and refed mice

Uncoupling protein content of brown adipose tissue mitochondria in fasted and refed mice

Cloning of cDNA encoding the uncoupling protein of brown adipose tissue mitochondria: lack of a mitochondrial targeting presequence

Cloning of cDNA encoding the uncoupling protein of brown adipose tissue mitochondria: lack of a mitochondrial targeting presequence

Are there one or two high-affinity binding sites for GDP in brown adipose tissue mitochondria?

Are there one or two high-affinity binding sites for GDP in brown adipose tissue mitochondria?

K+-H+ exchange and volume homeostasis in brown adipose tissue mitochondria.

K+-H+ exchange activity in hamster brown adipose tissue mitochondria is activated following depletion of matrix Mg2+ with the divalent cation ionophore A23187. Quinine inhibits K+-H+ exchange reversibly with an I50 of 22 microM, whereas mild treatment with N,N'-dicyclohexylcarbodiimide (DCCD) inhibits this activity irreversibly. In an attempt to label and identify the K+-H+ antiporter protein, brown adipose tissue mitochondria were incubated with [14C]DCCD and subjected to denaturing polyacrylamide gel electrophoresis and fluorography. We observed a labeled band of relative mol wt, 78,000, which satisfies criteria established in rat liver mitochondria for the identification of this carrier (W. H. Martin et al., J. Biol. Chem. 259: 2062-2065, 1984). Thus Mg2+ and quinine each protect the K+-H+ exchanger against both inhibition and binding by DCCD. Volume homeostasis in brown adipose tissue mitochondria, as in other mitochondria, requires a balance between K+ influx and efflux. We propose that regulation of the K+-H+ antiporter, the primary K+ efflux mechanism, plays a major role in this process.

Proteolytic digestion of the 32 000-Mr uncoupling protein in rat brown adipose tissue mitochondria

Proteolytic digestion of the 32 000-<i>M</i>r uncoupling protein in rat brown adipose tissue mitochondria

The effect of palmitoyl-CoA on GDP binding to brown adipose tissue mitochondria from lean and obese Zucker rats

The effect of palmitoyl-CoA on GDP binding to brown adipose tissue mitochondria from lean and obese Zucker rats

Flux control of fatty acid oxidation in brown adipose tissue mitochondria

Flux control of fatty acid oxidation in brown adipose tissue mitochondria

Influence of restricted food intake on brown adipose tissue function in genetically obese mice (genotype, ob/ob).

Measurements were made of cytochrome c oxidase activity and the GDP-binding capacity of mitochondria in brown adipose tissue of genetically obese mice and wild-type siblings, to estimate the thermogenic capacity of the tissue. The binding capacity was decreased in ad libitum fed obese animals compared with wild-type animals. Limited feeding of obese animals to restrict their body weight caused a large increase in the binding capacity of the tissue, which was greater than that in wild-type animals fed either ad limitum or on a limited diet. The decreased binding capacity of brown adipose tissue mitochondria in obese mice appears to be a consequence of ad libitum feeding and therefore not a cause of the obesity. Limit feeding of obese animals also corrected their characteristic hypothermia at low ambient temperature. The large increase in the thermogenic capacity of brown adipose tissue in obese animals, induced by limited feeding, may account for the vital improvement of their thermoregulation. However, close similarities were found between obesity hypothermia and hypothermia induced in wild-type animals by restraint. It is suggested that changes in posture caused by obesity, resulting in increased loss of body heat, may be important in the development of obesity hypothermia. Obese animals fed less than wild-type grained more weight than wild-type animals, indicating that the high thermogenic capacity of their brown adipose tissue did not function to regulate their calorie intake.

Brown adipose tissue thermogenesis, energy balance, and obesity.

The concept that thermogenesis in brown adipose tissue can play a role as an energy buffer has developed during the last 5 years. The history of this development is reviewed. Control of brown adipose tissue thermogenesis resides in regions of the brain, located primarily but not exclusively in the hypothalamus, that control the activity of the sympathetic nervous system in response to diet and to environmental temperature. Brown adipose tissue mitochondria are uniquely specialized for thermogenesis, possessing a specific proton leakage mechanism that is regulated by the concentration of fatty acids in the cells of the brown adipose tissue. The level of fatty acids is in turn controlled by the lipolytic action of noradrenaline on the tissue. Sympathetic stimulation also exerts a trophic influence on brown adipose tissue. Effective thermogenesis in brown adipose tissue is associated with leanness and decreased metabolic efficiency, as in the rat rendered hyperphagic and hypermetabolic, by either cold acclimation or cafeteria feeding. Conversely, food restriction is associated with suppressed thermogenesis in brown adipose tissue and increased metabolic efficiency. Defective brown adipose tissue thermogenesis is associated with obesity in a number of different types of obese animals. In three of these (the genetically obese fa/fa Zucker rat, the mouse with hypothalamic damage induced by gold thioglucose, the rat with a surgically induced hypothalamic lesion), diet-induced thermogenesis is defective in brown adipose tissue, but cold-induced thermogenesis is normal. In another type of obese animal, the genetically obese (ob/ob) mouse, control of brown adipose tissue is defective. Studies of this control are complicated by the frequency of torpor in the fed state.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of thyroid hormone in cold-induced changes in rat brown adipose tissue mitochondria.

The role of thyroid gland in cold-induced growth of brown adipose tissue and in cold-induced adaptive changes in brown adipose tissue mitochondria was investigated. Interscapular brown adipose tissue of thyroidectomized rats maintained at 28 °C was of normal size (protein, cytochrome oxidase content) and its mitochondria were normal, as judged from the level of GDP binding and the polypeptide composition. (GDP binds to a 32 000 dalton polypeptide component of the inner mitochondrial membrane. This component is part of the thermogenic proton conductance pathway. The level of GDP binding is a sensitive indicator of the thermogenic state of the tissue.) Brown adipose tissue mitochondria of thyroidectomized rats exposed to 4 °C for 15 h did not show the usual increase in GDP binding, an indication of a lack of a thermogenic response; the response was restored in thyroxine-treated thyroidectomized animals. In thyroidectomized rats treated with a low maintenance dose of thyroxine (25 μg/kg, s.c., three times per week) and acclimated to cold (4 °C) for 2 weeks, a normal growth of brown adipose (increase in protein and cytochrome oxidase) and normal changes in mitochondria (increase in GDP binding and an increase in the proportion of polypeptides of molecular weight 31 200 – 34 400) occurred. Treatment of intact rats with a large dose of thyroxine (1000 μg/kg, s. c., per day) resulted in a large increase in wet weight, mainly due to lipid accumulation since only small increases in protein and cytochrome oxidase and no change in DNA content occurred; mitochondrial GDP binding was decreased and polypeptide composition unchanged. It is concluded that thyroid hormone exerts a permissive effect on the cold-induced, noradrenaline-mediated, unmasking of GDP-binding sites in brown adipose tissue. The failure of the thyroidectomized rat to survive at 4 °C is probably primarily due to its inability to activate thermogenesis in its brown adipose tissue. Thyroid hormone does not appear to be involved, other than in a permissive way, in long-term cold-induced growth and mitochondrial changes in brown adipose tissue, since these occur normally in the presence of only small amounts of thyroxine in thyroidectomized rats and do not occur in intact rats treated with large amounts of thyroxine.

Ascorbic acid metabolism in diabetes mellitus

In contrast to normal subjects diabetic patients had very low plasma ascorbic acid and significantly high (p < 0.001) dehydroascorbic acid irrespective of age, sex, duration of the disease, type of treatment, and glycemic control. However, there was no significant difference between the mean leukocyte ascorbate concentrations of the two populations. The in vitro rates of dehydroascorbate reduction in the hemolysate and the erythrocyte reduced glutathione levels and the glucose-6-phosphate dehydrogenase activities, which regulate the dehydroascorbate reduction, were similar in normal and diabetic subjects. The turnover of ascorbic acid was higher in the diabetics than that in the normal volunteers. Experiments with diabetic rats indicated that the increased turnover of ascorbic acid was probably due to increased oxidation of ascorbate to dehydroascorbate in tissue mitochondria. Ascorbic acid supplementation at a dose of 500 mg per day for a brief period of 15 days resulted in an increase in the plasma ascorbate level temporarily, but it did not lower the blood glucose level of the diabetic patients.

Carotene in bovine milk fat globules: observations on origin and high content in tissue mitochondria.

The location and origin of carotenoids in bovine milk fat globules was investigated using spectral absorption of lipid solutions at 461 nm to quantitate carotene. Release of membrane from globules as a result of churning to butter or by freezing and thawing of the globules yielded membrane preparations which were devoid of carotene. Globule cores from these procedures exhibited carotene concentrations comparable to those in total milk lipids. Fractionation of lactating bovine tissue and analysis of lipid extracts revealed that the intracellular fat droplets have carotene concentrations approximating those of secreted globules. However, intracellular membranes of the tissue, particularly the mitochondria, are much richer in carotenoids than formative or secreted fat globules. The evidence indicates that bovine milk fat globules acquire carotene during their formation in the cell, but that some minor fraction of the total carotene may be extracted from the enveloping secretory membrane. Mean carotene values (microgram/g of lipid) for fractions from three samples of lactating tissue were: whole tissue 47, mitochondria 461, microsomes 69, cytosol 67, fat droplets 8, milk 9. One tissue analysis indicated that Golgi membranes contain somewhat more carotene than do microsomes.

Hepatic cellular hypoxia in murine peritonitis.

Reduced oxygen consumption and lactic acidosis were observed frequently in patients with peritonitis. This study was designed to evaluate whether reduced oxygen consumption is secondary to deficient oxygen delivery or is a function of primary injury to mitochondria. Peritonitis was produced in rats by cecal ligation and perforation. Animals were killed at 2, 4, and 6 hours and agonally. Oxygen utilization was studied polarographically in isolated hepatic mitochondria with glutamate, pyruvate, and succinate substrates. State 3, state 4, respiratory control index (RCI), and ADP:O ratios were determined. Whole tissue and isolated mitochondrial ultrastructure were examined by electron microscopy. Systemic blood pressure and oxygenation were monitored. Hepatic tissue oxygenation was examined using a surface oxygen electrode. Peritonitis resulted in acceleration of state 3 respiratory rates and increased respiratory control indices at all time intervals. Maximal respiratory control was observed at 4 hours with all substrates. Whole tissue mitochondria demonstrated mild swelling and thinning of membranes and matrix. Experimental and control isolates showed similar orthodox-to-condensed conformational changes. Hepatic tissue oxygenation declined to less than 10% of control by 6 hours, while arterial Po2 was unchanged. The conclusions of this study are that lethal peritonitis results in (1) no primary injury to the hepatic mitochondria, (2) increased efficiency of hepatic mitochondrial oxygen utilization, and (3) reduced hepatic tissue oxygenation. The exact mechanisms of defective oxygen delivery require further study.

An inverse relation between mitochondrial hexokinase content and phosphoglucomutase activity of rat tissues.

The hexokinase: fumarase ratios of mitochondria isolated from ten tissues of the rat were determined, and compared with the tissue content of phosphoglucomutase and phosphorylase, taken as representatives of enzymes concerned with glycogen metabolism. A generally inverse relationship was found between the mitochondrial hexokinase: fumarase ratio and phosphoglucomutase levels. The cytochrome: fumarase ratios were relatively invariant in these same mitochondria. The results are interpreted as indicating a specialization of mitochondria, with increased amounts to hexokinase being associated with the mitochondria in tissues exhibiting less dependence on glycogen metabolism, as judged from phosphoglucomutase levels.

Oxidative phosphorylation in brown adipose tissue mitochondria from rats kept under normal environmental conditions.

Based on criteria such as the ADP/O ratio and respiratory control by ADP, the energy-coupling efficiency of brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions for a long time decreased remarkably. The presence of bovine serum albumin, GTP, or ATP plus carnitine in the reaction medium markedly increased the efficiency of oxidative phosphorylation of brown adipose tissue mitochondria. Pre-treatment of brown adipose tissue mitochondria with 2% bovine serum albumin, GTP, or ATP plus carnitine caused a decrease in the amount of free fatty acids bound to the mitochondria from 13.1 to 7.0, 9.0, or 8.2 mug per mg protein, respectively. Removal of the free fatty acids by means of these pre-treatments resulted in restoration of efficient oxidative phosphorylation; there was a correlation between the amount of free fatty acids removed and the degree of recovery in the respiratory control ratio. The elimination of only a fraction of the free fatty acids, as little as 4 mug per mg protein, was sufficient to ensure respiratory control by ADP. It appears that the free fatty acids which lie mainly outside the inner mitochondrial membrane are responsible for the decrease in the efficiency of oxidative phosphorylation in brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions.

An electron paramagnetic resonance study of Mn 2+ uptake by the chick chorioallantoic membrane

Mn 2+ uptake in the chick chorioallantoic membrane, an embryonic epithelial tissue which transports Ca 2+ in vivo was studied using electron paramagnetic resonance (EPR). Mn 2+ was used as a paramagnetic analog for Ca 2+, since there is evidence that Mn 2+ is accumulated by the Ca 2+ transport mechanism. After 1.5 h of uptake the EPR spectrum of the Mn 2+ in the membrane indicated that 89 % of the Mn 2+ was in a spin-exchange form, indicating close packing of Mn 2+. The Mn 2+ spacing was estimated from the line width to be about 4.7 Å. The remaining Mn 2+ was very likely Mn 2+ hexahydrate. At pH 7.4 the spin-exchange spectrum tended to broaden when uptake was inhibited, while at pH 5.0 the spin-exchange spectrum was completely abolished in the presence of inhibitors. The EPR spectrum of Mn 2+ in the chorioallantoic membrane had a broader line width than that of Mn 2+ in isolated mitochondria, suggesting that in this tissue mitochondria are not directly involved in divalent cation transport. These EPR studies support the concept that divalent cations are sequestered in high concentrations from the rest of the cell contents during transcellular active transport.