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Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 253 records · Page 14Linked to original sources
PubMed1988

Relationship of muscular fatigue to pH and diprotonated Pi in humans: a 31P-NMR study.

Seventeen normal subjects performed maximal wrist flexion exercise with continuous monitoring of forearm muscle pH and H2PO4-, measured with 31P nuclear magnetic resonance, and muscle fatigue, expressed as a percentage of decline in maximal developed force. Four minutes of exercise (flexion duration = 1 s) reduced maximal developed force from 100 to 74 +/- 9% and pH from 6.99 +/- 0.04 to 6.17 +/- 0.33 and increased H2PO4- to 927 +/- 401% of resting levels. In all subjects, linear relationships were noted between developed force and pH (r = 0.90 +/- 0.08) and between developed force and H2PO4- (r = -0.89 +/- 0.08). Doubling the contraction duration to 2 s produced more rapid changes in developed force, pH, and H2PO4- but no change in the relationship of force to pH and H2PO4-. Two minutes of submaximal exercise before maximal exercise significantly reduced pH and increased H2PO4-. During subsequent maximal exercise, the relationship between developed force and H2PO4- remained unchanged. In contrast, the relationship between developed force and pH was shifted leftward; muscle pH remained lower throughout maximal exercise, and developed force remained comparable to that noted during control exercise. These observations suggest that muscle fatigue during intense short-term exercise is primarily caused by an increase in intramuscular H2PO4- rather than by a decrease in intramuscular pH.

Adult↗
PubMed1988

Application of 31P magnetic resonance spectroscopy to the study of athletic performance.

Magnetic resonance spectroscopy is a non-invasive and repeatable method of studying muscle metabolism. Magnetic resonance spectroscopy uses specific radiofrequency pulses in a strong magnetic field to determine the relative concentrations of chemical compounds in the sample. 31P Magnetic resonance spectroscopy provides indirect measures of phosphate compounds such as adenosine triphosphate (ATP), phosphocreatine and inorganic phosphate. Muscle intracellular pH can also be determined. Exercise tests can be performed in the magnet such that the metabolic response to steady-state exercise can be measured. The ratio of inorganic phosphate to phosphocreatine reflects the relative metabolic rate of mitochondrial respiration (V) and the extrapolated maximum capacity of oxidative metabolism (Vm). Normal humans vary considerably in their metabolic response to exercise. These differences are reflected in their Vms and the degree of acidosis during exercise. Active muscles in endurance trained athletes have higher Vms and faster recovery rates than normal controls. Preliminary studies have been done to assess muscle glycolytic capacity by measuring the degree of acidosis during ischaemic exercise. Exercise-induced muscle injury can be detected as an increased inorganic phosphate to phosphocreatine ratio in resting muscle. The increase in the inorganic phosphate to phosphocreatine ratio with injury reaches a peak 1 to 2 days after the injury and lasts for up to a week. Similar increases in the inorganic phosphate to phosphocreatine ratio occur in patients with destructive neuromuscular diseases. Thus changes in the resting inorganic phosphate to phosphocreatine ratio may be used to detect the degree of muscle injury following exercise. Levels of H2PO4- in muscle are thought to be important in causing muscle fatigue during exercise. As 31P magnetic resonance spectroscopy can measure H2PO4-, magnetic resonance spectroscopy has become a useful technique in the study of the metabolic causes of muscle fatigue. It may also be possible to identify the relative populations of fast twitch and slow twitch fibres in a skeletal muscle using pH changes measured with 31P magnetic resonance spectroscopy. Magnetic resonance spectroscopy using other nuclei, such as 1H, 13C and 23Na, have the potential to provide information on other metabolic changes which occur with exercise. Magnetic resonance spectroscopy has shown promise as a technique to monitor the effects of training, including overtraining, in specific muscle groups in athletes.

Energy Metabolism↗
PubMed1988

The bioenergetics of preservation of limbs before replantation. The rationale for intermediate hypothermia.

Of all tissues of the extremities, muscle is the least tolerant of ischemia. Hypothermia of tissue is considered beneficial for the maintenance of viability of muscle in amputated limbs before surgical replantation, but it has never been established that conventional cooling in an ice bath or its equivalent (temperature of tissue, approximately 1 degree Celsius) is the optimum level of hypothermia for minimizing metabolic derangement in ischemic muscle. In this study, we first defined the time course and level of metabolic derangement of muscle in twenty-eight ischemic hind limbs in cats at 22, 15, 10, 5, and 1 degree Celsius. The levels of adenosine triphosphate and phosphocreatine and the mean intracellular pH of the muscles in the lateral aspect of the thigh in each limb were monitored with phosphorus nuclear magnetic-resonance spectroscopy over time. The excised muscles from six freshly amputated legs of live humans were then similarly studied to determine whether muscles from cats and from humans exhibit comparable bioenergetic responses to hypothermic ischemia. A final series of ten ischemic hind limbs from cats was studied by nuclear magnetic resonance and muscle biopsy for direct biochemical assay of tissue energy metabolites to compare the metabolic benefits of two different methods of preserving limbs: continuous cooling in an ice bath, and a newly devised protocol for the rapid induction and maintenance of so-called intermediate (10 +/- 5 degrees Celsius) hypothermia of tissue. Ischemic skeletal muscle in cats exhibited a paradoxical metabolic response to extreme cold (1 degree Celsius). The rate of metabolic deterioration progressively declined with decreasing temperature of tissue to 10 degrees Celsius. However, at 5 degrees Celsius, no additional benefit was detected, and at 1 degree Celsius, there was a significant acceleration in the rates of degradation of adenosine triphosphate and phosphocreatine and in the production of lactate. The rate of degradation of adenosine triphosphate in human ischemic muscle was also faster at 1 degree Celsius than at 10 degrees Celsius. This paradoxical response is apparently due to a severe inhibition of the calcium pump of the sarcoplasmic reticulum of the muscle cell at temperatures of less than 5 degrees Celsius. The inhibition permits an efflux of calcium to the myofibrils, which stimulates both glycolysis and the degradation of adenosine triphosphate by myofibrillar adenosine triphosphatase.

Adenosine Triphosphate↗
PubMed1988

The compartment syndrome. An experimental and clinical study of muscular energy metabolism using phosphorus nuclear magnetic resonance spectroscopy.

In an experimental ischemic compartment syndrome in dogs, phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy was used to determine the tissue pressure threshold at which resting skeletal muscle begins to use anaerobic energy sources due to insufficient cellular oxygen delivery. The interactive effects of systemic perfusion pressure and moderate muscle trauma on this anaerobic threshold were also evaluated. The severity of cell injury produced by various degrees of compartment pressurization over an eight-hour period was concomitantly studied using muscle biopsy and electron microscopy. Clinical correlation of a preliminary patient series studied using 31P-NMR demonstrated that the threshold for cellular metabolic derangement in skeletal muscle subjected to increased tissue pressure was more closely associated with the difference between mean arterial blood pressure (MABP) and compartment pressure than with the absolute compartment pressure alone. The difference is termed MABP-compartment pressure, or delta P. The lowest delta P at which a normal cellular metabolic state can be maintained is approximately 30 mmHg in normal muscle and 40 mmHg in moderately traumatized muscle. It is imperative to interpret compartment pressure measurements in light of the degree of soft tissue trauma sustained and the patient's blood pressure, as well as the clinical signs and symptoms.

Animals↗
PubMed1988

In vivo 31P nuclear magnetic resonance measurement of chronic changes in cerebral metabolites following neonatal intraventricular hemorrhage.

The purpose of this study was to determine whether cerebral metabolic changes occur after intraventricular hemorrhage in the newborn. Five babies with bilateral grade 3 to 4 intraventricular hemorrhage were compared with 15 preterm infants without intraventricular hemorrhage. Cerebral high-energy phosphorus metabolites and intracellular pH were measured with in vivo 31P nuclear magnetic resonance spectroscopy. Spectra were collected initially within the first 2 weeks of life, and then every other week until discharged from the hospital. The phosphocreatine to inorganic phosphate ratio and the phosphocreatine to adenosine triphosphate ratio were significantly lower in the group with intraventricular hemorrhage, but differences in intracellular pH were not significant. Differences between babies with and without intraventricular hemorrhage varied with postconceptional age: in those with intraventricular hemorrhage, the phosphocreatine to adenosine triphosphate ratio was decreased at all postconceptional ages, and the phosphocreatine to inorganic phosphate ratio was lower in babies with intraventricular hemorrhage and younger than 30 weeks. Results of this study confirm the presence of chronic metabolic changes following intraventricular hemorrhage which may exacerbate neurologic damage after intraventricular hemorrhage in the newborn.

Adenosine Triphosphate↗
PubMed1987

Extended X-ray absorption fine structure studies on the iron-containing subunit of ribonucleotide reductase from Escherichia coli.

Iron K-edge X-ray absorption spectra were obtained on the protein B2, the small subunit of ribonucleotide reductase from Escherichia coli. Protein B2 contains a binuclear iron center with many properties in common with the iron center of oxidized hemerythrins. The extended X-ray absorption fine structure (EXAFS) measurements on protein B2 were analyzed and compared with published data for oxyhemerythrin. In protein B2 there are, in the first coordination shell around each Fe atom, five or six oxygen or nitrogen atoms that are directly coordinated ligands. In oxyhemerythrin there are six ligands to each iron. As in oxyhemerythrin, one of the ligands in the first shell of protein B2 is at a short distance, about 1.78 A, confirming the existence of a mu-oxo bridge. The other atoms of the first shell are at an average distance of 2.04 A, which is about 0.1 A shorter than in oxyhemerythrin. In protein B2 the Fe-Fe distance is in the range 3.26-3.48 A, and the bridging angle falls between 130 and 150 degrees. On the basis of these data, there is no direct evidence for any histidine ligands in protein B2, but the noise level leaves way for the possibility of a maximum of about three histidines for each Fe pair. The X-ray absorption spectrum of a hydroxyurea-treated sample was not significantly different from that of the native protein B2, which implies that no significant alteration in the structure of the iron site occurs upon destruction of the tyrosine radical.

Escherichia coli↗
PubMed1987

Kinetic, structural, and spectroscopic identification of geminate states of myoglobin: a ligand binding site on the reaction pathway.

Elementary steps or geminate states in the reaction of gaseous ligands with transport proteins delineate the trajectory of the ligand and its rebinding to the heme. By use of kinetic studies of the 765-nm optical "conformation" band, three geminate states were identified for temperatures less than approximately 100 K. MbCO, which is accumulated by photolysis between 1.2 and approximately 10 K, was characterized by our previous optical and X-ray absorption studies [Chance, B., Fischetti, R., & Powers, L. (1983) Biochemistry 22, 3820-3829]. Between 10 and approximately 100 K, geminate states that are also identified that have recombination rates of approximately 10(3) s-1 and approximately 10(-5) s-1 (40 K). Thus, it is possible to maintain a steady-state nearly homogeneous population of the slowest recombining geminate state, Mb, by regulated continuous illumination (optical pumping). Both X-ray absorption and resonance Raman studies under similar conditions of optical pumping show that the heme structure around the iron in Mb is similar to that of MbCO. In both geminate states, the iron-proximal histidine distance remains unchanged (+/- 0.02 A) from that of MbCO while the iron to pyrrole nitrogen average distance has not fully relaxed to that of the deoxy state. In MbCO the CO remains close to iron but not bound, and the Fe...CO angle, which is bent in MbCO (127 +/- 4 degrees C), is decreased by approximately 15 degrees [Powers, L., Sessler, J. L., Woolery, G. L., & Chance, B. (1984) Biochemistry 23, 5519-5523]. The CO molecule in Mb, however, has moved approximately 0.7 A further from iron. Computer graphics modeling of the crystal structure of MbCO places the CO in a crevice in the heme pocket that is just large enough for the CO molecule end-on. Above approximately 100 K resonance Raman studies show that this structure relaxes to the deoxy state.

Binding Sites↗
PubMed1987

1H- and 31P-NMR studies on smooth muscle of bullfrog stomach.

31P-NMR spectra of bullfrog stomach smooth muscle showed peaks for creatine phosphate (4.8 mumol X g-1 wet wt.), ATP (3.6), inorganic phosphate (Pi, 2.4), phosphomonoesters (3.0) and phosphodiesters (3.3). The intracellular pH was 7.3, and calculated from the chemical shift of Pi. 1H-NMR spectra of smooth muscle yielded peaks of 2.9 for lactate, 6.6 for total creatine (creatine phosphate + creatine) and methyl protons of choline tentatively assigned to glycerolphosphorylcholine or to membrane phospholipids. Creatine phosphate and ATP decreased under anaerobic conditions, and intracellular acidification was observed with the concomitant increase in lactate. 31P saturation transfer studies showed that saturation of the gamma-ATP resonance reduced the intensity of creatine phosphate to 60% of its control value, and the measured T1 value of creatine phosphate was 2.4 s with saturation. The calculated forward flux of the creatine kinase reaction (decomposition direction of creatine phosphate) was 0.77 mumol X g-1 wet wt. X s-1. The creatine kinase flux was approx. 100-times larger than the ATP turnover rate, calculated from the oxygen consumption rate with the assumption, P/O = 3. In conclusion, the creatine kinase reaction is at equilibrium in resting smooth muscle of bullfrog stomach.

Adenosine Triphosphate↗
PubMed1987

Structure of the copper sites in membrane-bound cytochrome c oxidase.

The structures of membrane proteins are difficult to obtain by crystallography and may be altered by the detergents used in their extraction. X-ray absorption spectroscopy has been used to identify the structures of the copper atoms of the membrane-bound enzyme in mitochondria and in submitochondrial particles at respective concentrations of 100 and 200 micron of molar copper. To within the experimental error, the x-ray absorption spectra of the copper atoms of the membrane-bound and the Yonetani (Yonetani, T. (1961) J. Biol. Chem. 236, 1680-1688) purified oxidase are identical; all detectable shells of the active site indicate no alteration of structural parameters. Significant differences are found when compared to the Hartzell-Beinert (Hartzell, R. C., and Beinert, H. (1974) Biochim. Biophys. Acta 368, 318-338) preparation. Extended x-ray absorption fine structure technology is now adequate for the direct studies of membrane proteins in situ in their natural environment.

Animals↗
PubMed1987

A new procedure for the purification of monodisperse highly active cytochrome c oxidase from bovine heart.

A simple and rapid method for the isolation of a large quantity of cytochrome c oxidase from bovine heart mitochondria was developed, based on selective solubilization of mitochondrial protein with first Triton and then lauryl maltoside. Gel filtration shows that the lauryl maltoside-solubilized oxidase preparation is in a hydrodynamically homogeneous state with a Stokes radius of 7.5 +/- 0.2 nm. It contains 8.0 mumol of haem (with an a/a3 ratio of 1)/g of protein. The catalytic constant (maximum turnover number) with respect to cytochrome c approaches 600 S-1. After further purification of the solubilized enzyme on a sucrose-gradient centrifugation, the purified enzyme has a haem content of 10.3 mumol/g of protein and eight major polypeptide bands shown on SDS/polyacrylamide-gel electrophoresis.

Animals↗
PubMed1987

Phosphorus magnetic resonance spectroscopy of partially blocked muscle glycolysis. An in vivo study of phosphoglycerate mutase deficiency.

In vivo phosphorus magnetic resonance spectroscopy was used to evaluate the changes in muscle bioenergetics in a patient with a partial glycolytic block. Phosphoglycerate mutase-deficient muscle showed the following evidence: Abnormal accumulation of sugar phosphates does occur, even when 6% enzyme activity is present. The elimination of sugar phosphates was faster than in complete glycolytic blocks. Mild intracellular acidosis occurred during ischemic exercise. The energy state was slightly low at rest but not during exercise. Postexercise recovery was mildly slowed. These findings suggest that phosphorus magnetic resonance spectroscopy can detect partial defects, as well as full glycolytic blocks, in muscle metabolism.

Adenosine Triphosphate↗
PubMed1987

Muscle energy metabolism in human phosphofructokinase deficiency as recorded by 31P nuclear magnetic resonance spectroscopy.

31P nuclear magnetic resonance studies of a patient with phosphofructokinase deficiency in muscle provided the following new findings: First, ATP metabolism is disturbed at rest and during exercise. At rest, ATP levels are lower than normal and continue to decline during exercise. Second, exercise kinetics are normal, suggesting a normal mitochondrial fuel supply although glycolysis is blocked. Third, no "phosphate trapping" is observed during prolonged low-level exercise. Fourth, postexercise recovery is abnormally prolonged by the slow dephosphorylation of sugar phosphates, which has an in vivo half-life of about nine minutes. These findings demonstrate how muscle tissue adapts to a block in a major bioenergetic pathway.

Adenosine Triphosphate↗
PubMed1987

Cardiac transfer function relating energy metabolism to workload in different species as studied with 31P NMR.

Cardiac metabolism was studied with 31P NMR in 7 dogs and 4 cats to determine whether animals adapted for different life-styles (stalk and sprint vs endurance running) respond to increased work loads (heart rate X blood pressure product) with different high-energy phosphate kinetics. Hearts were exposed via a left lateral thoracotomy under Nembutal anesthesia (40 mg/kg). Two-turned solenoid surface coils were placed on the left ventricles; pacing wires were sutured into the left ventricular apices. The femoral artery and vein were cannulated for blood pressure and arterial blood gas monitoring and fluid and drug infusion, respectively. Animals were placed in a plexiglass holder into a 2.1-T, 31-cm-bore, superconducting magnet. 31P spectra were obtained from the heart using respiratory and electrocardiogram gating. Cardiac work loads were changed by pacing the heart at 4, 4.5, and 5 Hz. Heart rate X blood pressure product "work" was correlated with Pi/PCr ratios. Dog hearts were more resistant than those of cats to changes in Pi/PCr with increasing work load. It is possible that animals adapted to different life-styles may have cardiovascular systems which are metabolically and mechanically adapted for different forms of stress. These differences may be elicited and effectively delineated using in vivo NMR techniques during various physiological interventions, such as pacing. The basis for these differences may be related to cardiac microvasculature or to intrinsic differences in enzyme kinetics. Delineation of these mechanisms may be helpful in the understanding of the physiological basis of cardiac function in health and disease.

Adaptation, Physiological↗
PubMed1987

31P and 1H NMR spectroscopy to study the effects of gallopamil on brain ischemia.

Studies were performed on 16 cats to evaluate the potential protective effects of Gallopamil on brain ischemia. Brain energy state was determined by 31P NMR and lactate concentration was determined by 1H NMR. Double-tuned surface coils (tuned to 35.8 and 88.4, respectively) were placed on the head after skin and muscle were removed from the calvarium. A 2.1-T, 25-cm-bore Oxford magnet interfaced to a Phosphoenergetics 250-80 spectrometer was used. The cats were bled to 50 mm Hg for 10 min with subsequent application of bilateral carotid occlusion for 10 min to produce ischemia. In all animals, brain energy state as measured by Pi/PCr and lactate concentrations were determined over 5-min intervals (before, during, and after the onset of ischemia). While Gallopamil did not prevent decreases in brain energy state or attenuate the rise in lactate concentration seen during ischemia, brain from animals treated with Gallopamil had a more rapid return of pHi to baseline during the recovery period. In Gallopamil-treated cats, higher levels of lactate were necessary to cause a similar decrease in pHi when compared to controls. The rate of lactate recovery to baseline levels was similar in both groups (control = -0.38 +/- 0.14 mM/min; Gallopamil = -0.44 +/- 0.32 mM/min). In conclusion, Gallopamil appears to lessen the acidosis caused by cerebral ischemia. In addition, we have demonstrated that multinuclear NMR spectroscopy is a powerful tool to study the effects of drugs on cerebral metabolism.

Animals↗
PubMed1987

Steady-state kinetic approaches to complex biological systems.

Steady-state kinetic approaches to study the biochemical systems have been extremely useful. In this paper we use this approach to explain the inhibition of electron transport in structurally bound multienzyme systems and in applying the work-energy cost transfer function to living tissues as studied by 31P NMR spectroscopy. We show that in both systems the steady-state approach leads to equations and predictions that are in accordance with the experimental data.

Animals↗
PubMed1987

Simultaneous 31P- and 1H-nuclear magnetic resonance studies of hypoxia and ischemia in the cat brain.

The objective of this study was to evaluate simultaneous 31P/1H nuclear magnetic resonance (NMR) spectroscopy as a technique for monitoring and correlating changes in brain energy metabolism during hypoxia and ischemia. Five cats were studied with a protocol that involved 20 min of hypoxia (PaO2 20 mm), 60 min of recovery, 10 min of hypoxia with relative ischemia (bilateral carotid occlusion, PaO2 20 mm), and 60 min of recovery. Bifrontal and biparietal electrocorticograms (ECoG) were monitored continuously during the entire protocol. The results demonstrate that the degree of metabolic response is different in individual cats, but a number of quantitative relationships between metabolic parameters are consistently observed for all cats. First, there is agreement between increases in lactate and changes in intracellular pH; the observed relationship corresponds to an in vivo cerebral buffer capacity of 29 mumol/g/pH unit. Second, the delayed recovery of PCr is due to the effect of metabolic acidosis on the creatine kinase equilibrium and not to a delayed recovery of the ATP/ADP ratio. Third, the observed rate of lactate clearance from the cell is zero-order (k = 0.36 mumol/g/min) for lactate levels greater than 5 microns/g and may be composed of both lactate efflux from the cell and lactate oxidation.

Adenosine Triphosphate↗
PubMed1987

Cerebral energy metabolism measured in vivo by 31P-NMR in middle cerebral artery occlusion in the cat--relation to severity of stroke.

The energy metabolism of the brain has been measured in a middle cerebral artery (MCA) occlusion model in the cat utilizing 31P-nuclear magnetic resonance (NMR). 31P-NMR spectra were serially obtained during 2 h of ischemia and a subsequent 4-h recovery period. The ratio of creatine phosphate (PCr) to inorganic phosphate (Pi) (PCr/Pi) showed a precipitous decrease in parallel with changes in electroencephalographic (EEG) amplitude in severe strokes during ischemia as well as during recirculation. Animals with mild strokes, as determined by EEG criteria, exhibited a much smaller decrease in PCr/Pi during ischemia. In the severe strokes, there was a splitting and significant shift of the Pi peak immediately after occlusion. In addition, the shifted Pi peak rapidly increased and remained elevated throughout the study. In the mild strokes, Pi also increased, but not as markedly. Intracellular pH determination by chemical shift of the Pi peak revealed a decrease from 7.1 to 6.2-6.3 during ischemia and the subsequent recovery period in the animals with severe strokes, whereas the pH in the animals with mild strokes did not show a significant change. A gradual decrease in adenosine triphosphate (ATP) to 57-79% of the control was exhibited in severely stroked animals during both the ischemia and the recovery period, whereas there was no change in ATP in the mild stroked animals. These results suggest that the dynamic process of pathophysiological changes in an MCA occlusion model in the cat leads to significant differences in cerebral metabolism between animals with mild and severe strokes.

Adenosine Triphosphate↗