Mitochondrial myopathies: defects in mitochondrial metabolism in human skeletal muscle.
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Adolescent↗
Biomedical subjects
J B Clark
Publications and source records attributed to J B Clark.
Scanning electron microscopy of the interaction between Haemophilus influenzae and organ cultures of rat trachea.
Organ cultures of rat trachea inoculated with either a type b or a non-capsulated strain of Haemophilus influenzae showed loss of ciliary activity and disruption of the mucosal surface. Examination of tissue pieces by scanning electronmicroscopy showed that mucosal damage was due to the sloughing of epithelial cells. Bacteria associated with the epithelial surface were seen infrequently and this, together with the observation that sloughed cells were usually free of adherent bacteria, indicated that bacterial attachment was not a necessary prerequisite for the production of tissue damage.
Animals↗
Effects of in vivo hypoxia on acetylcholine synthesis by rat brain synaptosomes.
Synaptosomes from normoxic and hypoxic rats were incubated aerobically in the presence and absence of veratridine. In the absence of veratridine, no significant difference was observed between the two types of preparation regarding either ATP/ADP ratio or 14CO2 or [14C]acetylcholine synthesis from D-[U-14C]glucose. However, in the presence of veratridine, significant reductions in the output of 14CO2 and [14C]acetylcholine by synaptosomes from hypoxic rats were apparent. It was concluded that irreversible metabolic lesions occur at the synapse as a result of hypoxia, which are apparent only when the metabolism of the preparation is accelerated to a level comparable with the maximal rate occurring in vivo. The presence of such lesions is further evidenced by the significant reductions in ATP/ADP ratio, 14CO2 output, and [14C]acetylcholine synthesis that occur in synaptosomes from hypoxic rats made anoxic in vitro and permitted to recover. Such decreases are not seen when synaptosomes from normoxic rats are similarly treated.
Acetylcholine↗
The diabetic Zucker fatty rat.
A noninsulin-dependent diabetes appeared in fatty rats in our Zucker rat colony. A breeding program yielded a genetic pattern of diabetes consistent with a dominant gene not closely linked to the fatty gene. Fatty males were more frequently affected than fatty females. Since no markers could be identified for heterozygous carriers and since affected fatty rats were 6 months old when diabetes appeared, the diabetic trait could not be sustained in our small colony. Glucose tolerance tests showed that the diabetic fatty rats had little increase in plasma insulin concentration after a glucose load was administered. Plasma insulin concentrations were unchanged relative to control fatty rats. Percentage body fat and plasma triglyceride values were decreased in fatty diabetic rats relative to control fatty rats, however, consistent with insulin resistance in fat and liver. The content of pancreatic insulin was markedly decreased in the diabetic fatty rat relative to either the ad libitum or diet-restricted fatty rats. The occurrence of a genetically based diabetes in a normally outbred colony underscores the importance of genetic traits that interact with obesity in determining diabetes in rodent models.
Adipose Tissue↗
Subarachnoid hemorrhage and intracranial aneurysms: a review of assessment and early management.
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Adult↗
In vitro 14C-leucine incorporation into nonsynaptic and synaptic rat brain mitochondria isolated by Ficoll gradients.
The in vitro incorporation of 14C-leucine by nonsynaptic and synaptic rat brain mitochondria purified by means of discontinuous Ficoll gradients has been characterised. The incorporation was linear for the first 45 min for both populations. Synaptic mitochondria showed a higher rate of incorporation than the nonsynaptic mitochondria at high concentrations of leucine. The incorporation was more effective in the presence of Mg2+ and inhibited by dinitrophenol. The incorporation was sensitive to chloramphenicol and insensitive to cycloheximide. Bacterial contamination was in any case lower than 1,000 colonies per ml after the incubation period. The incorporation was carried out in the presence of either an external ATP-generating system consisting of ATP, phosphoenolpyruvate and pyruvate kinase or with mitochondria respiring with oxidisable substrates plus ADP (state III). The rates obtained for incorporation in this state III were higher for all the substrates assayed (succinate, pyruvate and glutamate) than in the presence of exogenous ATP. The highest rate obtained was found when glutamate was the respiratory substrate. No significant metabolic oxidation of leucine occurs in either synaptic or nonsynaptic mitochondria in the presence of exogenous ATP. Glutamate did not increase leucine uptake in any mitochondrial populations.
Adenosine Triphosphate↗
The effects in vitro of hypoglycaemia and recovery from anoxia on synaptosomal metabolism.
Synaptosomes from several regions of the rat brain were found to exhibit half-maximal rates of 14CO2 output and [14C]acetylcholine synthesis from D-[U-14C]glucose at glucose concentrations approx. 50-fold lower than those required by the brain in situ. However, synaptosomal acetylcholine synthesis was found not to be directly proportional to substrate oxidation as measured by 14CO2 output. When synaptosomes had been exposed to anoxia in vitro, their metabolic indices (14CO2 and [14C]acetylcholine synthesis, and adenine nucleotide levels) were found not to be significantly different from control aerobic values, unless they had been subjected to veratridine depolarization. This is in accord with previous findings that neither the absolute metabolic rates nor the vulnerability to hypoxic damage exhibited by brain in situ is reflected by brain slices in vitro, unless these are stimulated by depolarization. The use of synaptosomes as a model for synaptic damage in vivo is discussed.
Acetylcholine↗
Toxic effects of human eosinophil products on isolated rat heart cells in vitro.
Rat heart cells and mitochondria were incubated with supernatants from eosinophils or neutrophils that had been stimulated with zymosan-C3b. Supernatants from eosinophils, but not neutrophils, were toxic to rat heart cells in a dose-dependent manner. This was associated with an increased O2 uptake, which was blocked by either 1 mM-cyanide or 100 microM-ouabain. Supernatants from eosinophils, but not neutrophils, caused a decrease in O2 uptake by rat heart mitochondria utilizing pyruvate (+ malate) but not other substrates. The activity of pyruvate dehydrogenase (EC 1.2.4.1) from rat heart was inhibited by Ca2+-free eosinophil supernatants. The activity of oxoglutarate dehydrogenase (EC 1.2.4.2) was also inhibited but not that of lipoamide dehydrogenase (EC 1.6.4.3). Prior incubation with heparin prevented these effects of eosinophil supernatants on heart cells, suggesting that they were caused by eosinophil cationic proteins. Other cationic proteins, including poly-L-lysine and poly-L-arginine were also toxic to rat heart cells, but these reduced O2 uptake. It was concluded that granulocyte secretion products containing eosinophil cationic proteins are toxic to isolated rat heart cells in vitro. This may be due to an initial increase in membrane permeability, which may lead to activation of (Na+ + K+)-dependent ATPase and increased O2 uptake. A second step may involve inhibition of pyruvate dehydrogenase by the same products, leading to a decreased O2 uptake. It is suggested that these mechanisms could contribute to the development of cardiac injury and myocardial disease in clinical situations where many degranulated eosinophils are present.
Animals↗
Mitochondrial encephalomyopathies: biochemical studies in two cases revealing defects in the respiratory chain.
We describe two patients with mitochondrial myopathies who presented with complex multisystem diseases predominantly affecting the central nervous system. In both cases the disease ran a fluctuating clinical course, eventually leading to profound impairment of intellectual function. In Case 1 dementia was associated with optic atrophy, absent pupillary responses, impaired eye movements and generalized dystonic rigidity without evidence of weakness or loss of muscle bulk. In Case 2 myoclonus preceded the onset of ataxia, generalized weakness and mental confusion by several years. Biochemical studies on isolated muscle mitochondria revealed defects in the mitochondrial respiratory chain which were located at NADH-CoQ reductase in Case 1, and at cytochrome b in Case 2. This study illustrates the potential value of muscle biopsy in the diagnosis of unusual and otherwise unexplained cerebral syndromes in man, even in the absence of muscle weakness.
Biopsy↗
Tyrosine hydroxylase activity in rat brain synaptosomes: direct measurement using high performance liquid chromatography.
By use of high performance liquid chromatography with electrochemical detection to measure dopamine production, tyrosine hydroxylase (EC 1.14.16.2) activity has been measured in rat brain synaptosomes from striatum and forebrain. Normal specific activities three- to fivefold higher than previously reported in the literature for radiochemical methods of assay were found. It is suggested that synaptosomes contain a significant amount of endogenous substrate for tyrosine hydroxylase, which causes dilution of the added labelled tyrosine and hence underestimation of the activity of this enzyme when radiochemical methods are used.
Animals↗
Noncorrelation of choline kinase or ATP citrate lyase with cholinergic activity in rat brain.
The activity of choline acetyltransferase was used as an index of cholinergic structures in regions of rat brain. The activities of ATP citrate lyase and choline kinase correlated poorly with cholinergic activity in whole tissue fractions, contrasting with the good correlation between acetylcholinesterase and choline acetyltransferase. Choline acetyltransferase was preferentially localised in synaptosomes prepared from regions of high (striatum) or intermediate (cortex, medulla oblongata/pons) cholinergic activity. In general, this was not true for either choline kinase or ATP citrate lyase.
ATP Citrate (pro-S)-Lyase↗
Age-related changes in insulin receptor regulation in liver membranes from Zucker fatty rats.
Hyperinsulinemic obese rodents have been shown to have reduced insulin binding to liver plasma membranes, a finding consistent with the model of down-regulation of insulin receptors by hyperinsulinemia. In contrast, hepatocytes from the hyperinsulinemic Zucker fatty rat were reported to have insulin binding equivalent to that of lean littermates. We have isolated liver plasma membranes from Zucker fatty rats 10 weeks, 5 months, and 1 yr of age and from fatty rats diet restricted until 5 months and 1 yr of age. We found no evidence for down-regulation of hepatic insulin receptors at 10 weeks of age. However, at 5 months and 1 yr of age there was marked down-regulation evident in isolated liver plasma membranes. Scatchard plots of the data are consistent with a decreased number of receptors rather than changes in receptor affinity accounting for the decreased binding. Diet restriction of the fatty rats resulted in lower plasma insulin levels and less marked down-regulation of hepatic insulin receptors. Our results are consistent with the hypothesis that in developing obesity there is a pattern of developing insulin resistance, first seen in muscle, later in fat, and finally in liver. Regulation of insulin receptors by hyperinsulinemia is probably less important than prior alterations in tissue metabolism by hyperinsulinemia in accounting for insulin resistance.
Aging↗
Studies on the regulation of insulin binding by liver plasma membranes from Zucker fatty rats.
The hyperinsulinemia of obese rodents has been associated with a reduced number of hepatic insulin receptors except in hepatocytes from fatty Zucker rats. We isolated liver plasma membranes from 10-11-wk-old lean and fatty Zucker rats, some of which were injected with streptozotocin 2--4 wk earlier. We have determined that although the number of hepatic insulin receptors is not reduced in young hyperinsulinemic fatty Zucker rats, the number of receptors can be increased when the hyperinsulinemia of the fatty rats is reduced by treatment with streptozotocin. In the fatty rats, this reduction in circulating insulin is accompanied by a reduction in plasma triglyceride concentration, consistent with a decreased stimulation of hepatic lipogenesis. Competitive binding curves for insulin were obtained with isolated liver plasma membranes and 125I-insulin. Analysis of these curves for affinity and number of receptors indicated that the number of insulin receptors was unchanged for the fatty control rats relative to the lean control rats but was increased in streptozotocin-treated animals. These data indicate that the regulation of hepatic insulin receptors is altered in the young fatty Zucker rat as characterized by a lack of downregulation of hepatic insulin receptors by hyperinsulinemia and an upregulation of hepatic insulin receptors at insulin concentrations higher than those found in lean rats. An altered state of hepatic insulin receptor regulation may be characteristic of developing obesity.
Animals↗
Mitochondrial/cytosolic carbon transfer in the developing rat brain.
The rates of citrate and acetoacetate efflux from rat brain mitochondria (synaptic and free) utilizing different substrates (pyruvate, 3-hydroxybutyrate or acetoacetate) under different conditions have been studied as a function of development. In general there were no marked differences in the acetoacetate efflux rates between 'free' and 'synaptic' brain mitochondria whereas citrate efflux rates were usually higher in 'free' mitochondria. Developmental studies with brain mitochondria utilizing 3-hydroxybutyrate + malate showed a profile for acetoacetate efflux which was at a peak at weaning (21 days) and then decreased by 50% in the adult state. Similar studies measuring citrate efflux showed little change as the brain developed, but when pyruvate + malate were used as substrates the citrate efflux doubled during the period 5--20 days and was then maintained in the adult state. Phenylpyruvate was found to inhibit both acetoacetate and citrate efflux from 21-day-old and adult rat brain mitochondria when they used either 3-hydroxybutyrate or pyruvate as substrate. It is concluded that ketone bodies may be potentially as effective, if not better, than glucose in the brain of the suckling rat as precursors of cytosolic biosynthetic activities whereas in the adult rat brain, ketone bodies are relatively poor precursors of these activities.
Acetoacetates↗
Mitochondrial myopathy. Biochemical studies revealing a deficiency of NADH--cytochrome b reductase activity.
This paper presents biochemical data upon a young male with a mitochondrial myopathy characterised by weakness, severe exercise intolerance, muscle wasting and exercise-induced lactic acidaemia. Two similar cases have been previously documented (Morgan-Hughes et al. 1979). This report more precisely locates the mitochondrial defect. In vitro mitochondrial studies show markedly decreased respiratory rates with all NAD-linked substrates whilst that with flavin-linked succinate is normal. Oxidative phosphorylation is normally coupled. Mitochondrial cytochrome components as determined by low temperature spectroscopy are normal. NADH-ferricyanide reductase and primary dehydrogenase activities are present at levels far in excess of that required to support normal NAD-linked substrate oxidation rates. Intramitochondrial NAD levels are similar to those found in other mammalian muscle. It is proposed therefore that the mitochondrial defect is situated between NADH dehydrogenase and the CoQ--Cytochrome b complex; possibly being a derangement of a non-haem iron sulphur centre.
Adult↗
The postnatal development of brain metabolism.
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Aging↗