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Biomedical subjects

J B Clark

Publications and source records attributed to J B Clark.

At least 19 recordsLinked to original sources
PubMed1992

Evidence for intramitochondrial complementation between deleted and normal mitochondrial DNA in some patients with mitochondrial myopathy.

Twenty-three patients with mitochondrial myopathies and mitochondrial DNA deletions in muscle were studied by means of deletion mapping and sequencing, histochemistry and polarography. Histochemistry showed significantly less focal cytochrome oxidase deficiency relative to number of ragged red fibres when the deletion did not involve reading frames for cytochrome oxidase subunits. Polarography in such patients showed defects exclusively involving complex I, in contrast to the others with larger deletions who generally had more diffuse respiratory chain defects. Analysis of other published histochemical data showed similar findings to our own. It is concluded that translation of a proportion of deleted mitochondrial DNAs occurs in at least some patients with mitochondrial DNA deletions, implying that deleted and normal mitochondrial genomes share transfer RNAs within mitochondria in such cases.

Base Sequence↗
PubMed1992

One-step immunoaffinity purification of complex I subunits from beef heart mitochondria.

Polypeptides of beef heart mitochondrial complex I were isolated from 15 mg of solubilized beef heart mitochondria using antibodies immobilized on an agarose chromatography column. The preparation was examined by SDS electrophoresis and Western blotting using affinity-purified antibodies to complex I and compared to beef heart complex I purified according to the conventional method of Hatefi and Rieske. There was a high degree of homology between the two preparations as judged by SDS-polyacrylamide electrophoresis and by immunoblotting with seven affinity-purified antibodies to various complex I subunits. This method could be applied to the preparation of complex I subunits from small samples such as human muscle biopsy specimens.

Animals↗
PubMed1992

Effect of lidocaine on somatosensory evoked response and cerebral blood flow after canine cerebral air embolism.

BACKGROUND AND PURPOSE: Victims of air embolism often recover rapidly on hyperbaric treatment then deteriorate again, even if hyperbaric treatment is continued. In previous animal experiments, lidocaine has been shown to improve recovery of somatosensory evoked response amplitude after air embolism. However, animals in these experiments rarely deteriorated. We have shown that the induction of air embolism and transient hypertension in canines produces deterioration despite hyperbaric treatment, and we decided to test the effect of lidocaine on somatosensory evoked potential recovery and cerebral blood flow in this model. METHODS: Dogs were treated with repeated doses of lidocaine or equivalent volumes of saline during hyperbaric therapy after internal carotid air embolism and transient hypertension. The investigators were unaware of treatment group assignment during the experiments. The amplitude of the median nerve somatosensory evoked potential and cerebral blood flow measured with carbon-14-labeled iodoantipyrine autoradiography were used to assess effect of therapy. RESULTS: Lidocaine-treated dogs recovered 60 +/- 10% (mean +/- 95% confidence limits) of the baseline somatosensory evoked potential amplitude 220 minutes after air embolism; saline-treated dogs recovered 32 +/- 10% (a significant difference at p less than 0.01). Lidocaine-treated dogs also had higher cerebral blood flow values than saline-treated dogs 220 minutes after air embolism. CONCLUSIONS: Lidocaine ameliorated the delayed deterioration of evoked potential associated with air embolism and hypertension in this canine model. The improved cerebral blood flow may be a mechanism of action of lidocaine or an associated effect of improved neuronal survival.

Animals↗
PubMed1992

Treatment of experimental NADH ubiquinone reductase deficiency with menadione.

Chronic administration of diphenylene iodonium (DPI) to rats has been shown to model the characteristics of mitochondrial myopathy. Using this model the efficacy of menadione therapy has been assessed. Menadione treatment of rats injected with DPI was associated with improved weight gain and increased survival rate. This was accompanied by an improvement in muscle function as judged by analysis of isometric twitch tension of the gastrocnemius muscle (1 Hz for 20 min). The decline in phosphocreatine (PCr) levels in the gastrocnemius muscle during stimulation and delayed recovery in PCr after stimulation were similar in the menadione treated and untreated models. Menadione treatment of the DPI model resulted in a resting intramuscular pH significantly lower than control or untreated DPI rats, but a similar decline in intramuscular pH to the DPI rats during stimulation. The changes in metabolite levels were broadly similar in both the menadione treated and untreated DPI models following stimulation, although the changes, except for increased lactate concentration, were generally less marked in the menadione-treated DPI model.

Adenosine Diphosphate↗
PubMed1992

Spatial disorientation and dysfunction of orientation/equilibrium reflexes: aeromedical evaluation and considerations.

Loss of spatial awareness has been implicated as a direct causal factor in 4-10% of serious aircraft mishaps and 10-20% of fatal aircraft mishaps (7). Spatial disorientation in flight usually results from misperception of visual, vestibular, or proprioceptive cues. Pathologic causes have rarely been implicated. A student naval aviator with recurrent loss of spatial awareness due to a defective vestibulo-ocular reflex (VOR), presumably from vestibular neuronitis in adolescence, is reported. His chief complaint, an inability to focus on the instrument panel during turbulent instrument meteorological conditions (IMC), resulted in spatial disorientation and adverse flight attitude. A simple test of visual-vestibular interaction, the dynamic visual acuity test, could identify a defective vestibulo-ocular reflex in aviation personnel. An absent or defective vestibulo-ocular reflex has potential for disorientation in instrument flight. A comprehensive vestibular function test battery is indicated in individuals with recurrent or overwhelming spatial disorientation who fail a screening dynamic visual acuity test. The aeromedical disposition of vertigo and dysequilibrium is discussed.

Adult↗
PubMed1991

Possible horizontal transfer of Drosophila genes by the mite Proctolaelaps regalis.

There is strong inferential evidence for recent horizontal gene transfer of the P (mobile) element to Drosophila melanogaster from a species of the Drosophila willistoni group. One potential vector of this transfer is a semiparasitic mite, Proctolaelaps regalis DeLeon, whose morphology, behavior, and co-occurrence with Drosophila are consistent with the properties necessary for such a vector. Southern blot hybridization, polymerase chain reaction (PCR) amplification, and DNA sequencing showed that samples of P. regalis associated with a P strain of D. melanogaster carried P element sequences. Similarly, Drosophila ribosomal DNA sequences were identified in P. regalis samples that had been associated with Drosophila cultures. These results have potentially important evolutionary implications, not only for understanding the mechanisms by which genes may be transferred between reproductively isolated species, but also for improved detection of some host-parasite and predator-prey relationships.

Animals↗
PubMed1991

Fluorocarbon perfusion of the isolated rat brain: measurement of tissue spaces, EEG and oxygen uptake.

Previously, we have used the isolated perfused rat brain (IPRB) to demonstrate authentic cerebral synthesis of the lipid mediator platelet-activating-factor (Kumar, R., Harvey, S.A.K., Kester, M., Hanahan, D.J. and Olson, M.S. (1988) Biochim. Biophys. Acta 963, 375-383). The present study demonstrates that this fluorocarbon perfusion technique maintains the integrity of the blood-brain barrier (BBB), as evidenced by the small volume (1.77-3.33%) accessible to [carboxyl-14C]inulin. 51-66% of the brain was accessible to 3H2O, except for the spinal cord which is poorly perfused (16% accessible to 3H2O). There is no effective perfusion of muscle tissue associated with the preparation (less than 6% accessible to 3H2O). Fast Fourier Transform analysis of digitized EEG data showed that in low frequency bands (less than 7.5 Hz) the IPRB had reduced electrical activity relative to the whole conscious animal. The GABA antagonist bicuculline, which has convulsant effects in vivo, causes a 3-4-fold increase in overall (root-mean-square) electrical activity, but decreases further the relative amplitude of low frequencies. With appropriate corrections, measurement of the oxygen consumption of the IPRB can be made without the necessity for venous cannulation. Oxygen consumption of the IPRB is flow-dependent. At a perfusion rate of 1.54 ml/min per g, unstimulated oxygen consumption of the IPRB is 2.07-2.23 mumol/min per g, or 67-72% of the consumption of the brain in vivo. Administration of bicuculline to the IPRB causes a 31% increase in lactate efflux, but only a 15% increase in oxygen uptake, suggesting that the preparation becomes functionally ischemic. Measurement of ATP/ADP levels in control and bicuculline-treated IPRBs confirms this. Other workers have used the IPRB as a model for the cerebral effects of pharmacological agents and of metabolic insult. The present study shows that under various experimental conditions oxygen uptake, analytical EEG measurements, and the integrity of the blood-brain barrier all can be monitored.

Animals↗
PubMed1991

Reoxygenation-dependent decrease in mitochondrial NADH:CoQ reductase (Complex I) activity in the hypoxic/reoxygenated rat heart.

Reoxygenation of the hypoxic myocardium results in a number of processes, including an O2-dependent increase in total tissue Ca2+ and cell lysis in which mitochondrial electron transport plays a key role. In the present study we have isolated mitochondria from perfused rat hearts subjected to hypoxia and found no change in their respiratory function relative to controls. In contrast, mitochondria isolated immediately after reoxygenation of hypoxic-perfused hearts exhibited a specific and significant decrease in NADH:CoQ reductase (Complex I; EC 1.6.5.3) activity, as measured both polarographically and spectrophotometrically. Isolated cardiomyocytes subjected to a similar protocol of hypoxia/reoxygenation also exhibited a specific decrease in Complex I activity. Myocardial perfusion with media containing Ruthenium Red protected against the reoxygenation-dependent loss of Complex I activity. These observations taken together suggest that mitochondrial Ca2+ uptake on reoxygenation is implicated in the mechanism of the specific loss of Complex I activity.

Animals↗
PubMed1991

Protection of ischaemic synaptosomes from calcium overload by addition of exogenous lactate.

In depolarised anoxic synaptosomes, in which lactate production was significantly raised compared with normoxic conditions, calcium uptake, net acetylcholine release, and the intrasynaptosomal calcium concentration were all significantly lowered. In contrast, lactate production in synaptosomes incubated under aglycaemic- and ischaemic-type conditions was significantly lower and basal calcium uptake, acetylcholine release, and intrasynaptosomal calcium concentration were elevated compared with normoxia. In addition, the increase in intrasynaptosomal calcium concentration under the ischaemic-type condition appeared to be greater than could be accounted for by the rise in calcium uptake alone. Intrasynaptosomal pH reflected the lactate production under each condition investigated. Addition of exogenous lactate to normoxic synaptosomes mimicked the effects observed in anoxia, suggesting that lactate itself may have blocked the calcium uptake, inhibiting the rise in intrasynaptosomal calcium and acetylcholine release occurring in depolarised anoxic synaptosomes. When lactate was added to ischaemic synaptosomes, the large rise in intrasynaptosomal calcium concentration, calcium uptake, and acetylcholine release were decreased, suggesting that lactate may have a protective role in preventing cell death by calcium overload under ischaemic-type conditions. Evidence is presented to suggest that the effect of L-lactate was due to the lactate moiety itself rather than the associated acidosis.

Acetylcholine↗
PubMed1991

Lactate utilization by isolated cells from early neonatal rat brain.

The utilization of lactate, glucose, 3-hydroxybutyrate, and glutamine has been studied in isolated brain cells from early newborn rats. Isolated brain cells actively utilized these substrates, showing saturation at concentrations near physiological levels during the perinatal period. The rate of lactate utilization was 2.5-fold greater than that observed for glucose, 3-hydroxybutyrate, or glutamine, suggesting that lactate is the main metabolic substrate for the brain immediately after birth. The apparent Km for glucose utilization suggested that this process is limited by the activity of hexokinase. However, lactate, 3-hydroxybutyrate, and glutamine utilization seems to be limited by their transport through the plasma membrane. The presence of fatty acid-free bovine serum albumin (BSA) in the incubation medium significantly increased the rate of lipogenesis from lactate or 3-hydroxybutyrate, although this was balanced by the decrease in their rates of oxidation in the same circumstances. BSA did not affect the rate of glucose utilization. The effect of BSA was due not to the removal of free fatty acid, but possibly to the binding of long-chain acyl-CoA, resulting in the disinhibition of acetyl-CoA carboxylase and citrate carrier.

3-Hydroxybutyric Acid↗
PubMed1991

Synthesis and anti-inflammatory activities of some N-[pyridyl(phenyl)carbonylamino]-tert-butyl/phenyl-1,2,3,6- tetrahydropyridines.

Nucleophilic attack of tert-butyl/phenylpyridines 3 on 1-chloro-2,4-dinitrobenzene 4 results in the formation of tert-butyl/phenyl substituted 2,4-dinitrophenylpyridinium chlorides 5. Benzoyl hydrazide and pyridyl acid hydrazides 6 were reacted with the pyridinium chlorides 5 furnishing the 2,4-dinitroanilino derivatives 7, which were subsequently hydrolyzed with water: p-dioxane to yield N-[pyridyl(phenyl)carbonylimino]-tert-butyl/phenylpyridinium ylides 8. The title compounds 9, N-[pyridyl(phenyl)carbonylamino]-tert-butyl/phenyl-1,2,3,6- tetrahydropyridines, were obtained by sodium borohydride reduction of the pyridinium ylides 8. The anti-inflammatory activities of compounds 9a-p were determined using the carrageenan-soaked sponge model of inflammation in Sprague Dawley rats. All compounds tested showed moderate to good anti-inflammatory effects compared to indomethacin. Compounds 9b, 9c and 9p were the most active analogs of the group in this model.

Animals↗
PubMed1991

The molecular pathology of human respiratory chain defects.

Deletions of the mitochondrial genome were identified in 21 out of 58 patients (36 percent) with mitochondrial myopathies, 47 of whom had defects in the mitochondrial respiratory chain. In cases with Complex I defects, the deleted regions of mtDNA, were confined to structural genes encoding Complex I subunits but additionally involved the intervening tRNA genes and in one case included the large and small rRNA genes. In cases with more extensive loss of respiratory chain function, the deletions eliminated genes encoding subunits of Complexes I, IV and V, as well as several tRNAs. Complex I and Complex IV polypeptides were usually normal in deleted cases. This was in contrast to 7 out of 22 patients without detectable mtDNA deletions, who showed specific deficiencies of subunits encoded by nuclear genes. Further studies in one of these cases pointed to defective translocation of the Rieske precursor from the cytosol into the mitochondria. The genetic basis of the disease in 15 cases without detectable deletions or specific subunit deficiencies, remains unknown. The multiple biochemical abnormalities encountered in these cases would be consistent with more subtle alterations of the mitochondrial genome.

Chromosome Deletion↗
PubMed1990

The molecular pathology of respiratory-chain dysfunction in human mitochondrial myopathies.

Some of the different molecular pathologies of respiratory-chain dysfunction in human mitochondrial myopathies will be reviewed in relation to the findings in 58 cases. Deletions of mitochondrial DNA were identified in 21 cases [36%]. There was some correlation between the sites of the deletion and the mitochondrial biochemistry in patients with defects of Complex I but not in cases with more extensive loss of respiratory chain activity. Complex I and Complex IV polypeptides were usually normal in deleted cases. Non-deleted cases, however, often showed specific subunit deficiencies which involved the products of both nuclear and mitochondrial genes. Immunoblots of respiratory-chain polypeptides in one case pointed to defective translocation of the Rieske precursor from the cytosol into the mitochondria. The pathogenic role of circulating autoantibodies to specific matrix proteins and the nature of the target antigens in two patients with mitochondrial encephalomyopathies and respiratory-chain dysfunction will also be discussed.

Autoantibodies↗
PubMed1990

Epizootiology of neoplasms in bony fish of North America.

Over the past 25 years, there have been an increasing number of fish tumor epizootics recognized in discrete geographical areas in North America. This is consistent with an association between tumor development in fish and exposure to waterborne contaminants as a result of increased industrialization. Reports of fish tumor epizootics from the literature, plus acquisitions at the Registry of Tumors in Lower Animals, Smithsonian Institution originate from 41 geographical regions in North America. Epizootics of hemic, neural, connective tissue, and gonial neoplasms seem unrelated to environmental pollution, but epizootics of hepatic and epidermal neoplasms appear to be caused or strongly influenced by environmental pollution. The 14 species with epizootic liver tumors are all bottom feeding fish, and tumor-bearing fish are generally located in areas where chemical contaminants are concentrated. Epidermal neoplasms are also found in fish near polluted areas, but a direct cause-and-effect link with chemical carcinogens is not clear.

Animals↗