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Biomedical subjects

G K Radda

Publications and source records attributed to G K Radda.

At least 19 recordsLinked to original sources
PubMed1992

Endoplasmic reticulum: the major contributor to the PDE peak in hepatic 31P-NMR spectra at low magnetic field strengths.

31P-NMR spectra of liver in vivo, subcellular fractions and model systems were acquired in order to characterise further the hepatic phosphodiester peak seen at low magnetic field strengths previously shown to be predominantly due to phospholipid bilayers. The data obtained in this study in vitro suggested that the phospholipid membranes of the endoplasmic reticulum provide the dominant contribution to this phosphodiester peak. Support for this hypothesis was provided by experiments on rats. Phenobarbitone, which is known to induce proliferation of the endoplasmic reticulum produced a considerable increase in intensity of the phosphodiester peak in liver spectra in vivo.

Animals↗
PubMed1992

Skeletal muscle Pi transport and cellular [Pi] studied in L6 myoblasts and rabbit muscle-membrane vesicles.

In the rat skeletal myoblast line L6 and in a rabbit skeletal muscle sarcolemma/t-tubule vesicle preparation, [32P]Pi uptake was largely dependent on the transmembrane Na gradient. Na-dependent [32P]Pi uptake had a hyperbolic relationship to [Pi] and [Na], being half-maximal at 0.2-0.3 mM [Pi] and at 25-40 mM [Na]. In vesicles the Na-dependence suggests that approx. two Na are transported with each Pi, but the inhibition of [32P]Pi uptake at high pH suggests that the Pi monoanion is the transported form. Together these imply electrogenic transport and this is confirmed by the results of manipulating the vesicle membrane potential. Thus, electrogenic Na-Pi co-transport exploits both the sodium gradient and the cell membrane potential to maintain muscle cellular [Pi] against an unfavourable electrochemical gradient. The low [Pi] for half-maximal flux may partly explain the small effect of altered extracellular [Pi] on cellular [Pi]. In L6 myoblasts most 32P was first detectable in an organic phosphate pool rather than cellular Pi, while the specific activity of cell Pi rapidly reached 40% of that of extracellular Pi and was stable for at least 3 h. These results are discussed in terms of the organisation of cellular phosphate metabolism.

Animals↗
PubMed1992

Changes in phosphatidylethanolamine metabolism in regenerating rat liver as measured by 31P-NMR.

31P-NMR spectra of regenerating rat liver in vivo show increases in resonance intensities in the phosphomonoester (PME) region and decreases in the phosphodiester (PDE) region as early as 12 h post partial hepatectomy, which return to normal by 8 days. The compounds primarily responsible for these changes have been identified in perchloric acid extracts as the phosphomonoester phosphoethanolamine and the phosphodiester glycerophosphoethanolamine (GPE), indicating altered phosphatidylethanolamine metabolism. A corresponding increase in diacylglycerol (DAG) levels during regeneration indicates a possible role for a phosphatidylethanolamine-specific phospholipase C in cellular proliferation. These results suggest that changes in phospholipid metabolites previously associated with neoplastic tissue can also be induced by normal tissue undergoing rapid cellular proliferation. The spectral changes observed in the regenerating rat liver are similar to changes seen in spectra from the livers of human patients in several disease states, indicating that 31P-NMR may allow non-invasive study of cell turnover in liver disease.

Adenosine Triphosphate↗
PubMed1992

Determination of free creatine and phosphocreatine concentrations in the isolated perfused rat heart by 1H- and 31P-NMR.

To measure free creatine in the isolated perfused rat heart, the concentration of phosphocreatine, and phosphocreatine plus creatine (sigma Cr) were measured by 31P- and 1H-NMR, respectively. Quantification was performed in the presence and absence of an intraventricular balloon filled with a known amount of PCr, which acted as an external standard. Total (free plus bound) phosphocreatine and creatine were measured by HPLC analysis of extracts from the same hearts, freeze-clamped at the end of the perfusions. A greater concentration of creatine (mumol/g dry wt.) in the perfused rat heart was measured by HPLC analysis (40.3 +/- 2.38 (11)) as compared to NMR (34.6 +/- 1.95 (11)), whilst no significant difference was observed in the measurement of phosphocreatine between the two assay methods. Consequently, a greater sigma Cr was measured by HPLC. This work suggests that the majority of Cr in the heart is NMR visible and unbound, so available to interact with creatine kinase. The lower free ADP concentration calculated from NMR measurements (53.3 +/- 3.80 microM (9)) was not significantly different from that determined by HPLC analysis (56.9 +/- 5.90 microM (9)). This suggests that the concentration of free ADP in the heart is higher than values where it can regulate oxidative phosphorylation most effectively.

Animals↗
PubMed1992

31P magnetic resonance spectroscopy detects a functional abnormality in liver metabolism after acetaminophen poisoning.

Eighteen patients with acetaminophen poisoning were studied with 31P magnetic resonance spectroscopy to measure phosphorus-containing metabolites in their livers. The concentrations of all magnetic resonance-detectable metabolites fell in parallel with a decrease in the synthetic ability of the liver, indicated by the prothrombin time ratio (international normalized ratio). In particular, ATP fell to about 20% of its normal concentration in severely affected patients, as did the phosphodiester signal, which is thought to arise mainly from the endoplasmic reticulum in the liver. The correlation between ATP levels and international normalized ratio suggests that the international normalized ratio is a more accurate measure of the number of viable hepatocytes than are other biochemical tests.

Acetaminophen↗
PubMed1992

A 31P-NMR study of muscle exercise metabolism in mdx mice: evidence for abnormal pH regulation.

We have studied exercise metabolism in vivo in the mdx mouse model of Duchenne muscular dystrophy with 31P-nuclear magnetic resonance spectroscopy. Intracellular pH, ratios of phosphocreatine (PCr) to ATP and PCr to inorganic phosphate (P(i)) expressed as PCr/ATP and PCr/(PCr+P(i)) as well as tension generated at the Achilles tendon were measured during sciatic nerve stimulation. Tension was similar between the mdx and control strain C57Bl/10ScSn at 10 Hz stimulation but slightly higher than the control at 100 Hz. The PCr/ATP and PCr/(PCr+P(i)) ratios were significantly reduced in mdx vs. control muscle during exercise. Although resting muscle pH in mdx mice is more alkaline than normal muscle, the pH of mdx muscle during exercise is reduced relative to controls, as is the rate of pH recovery. Total lactate is not elevated in the cells and so it is argued that there is a reduction in the capacity to export proton equivalents in muscles of mdx mice which could be caused by an elevation in intracellular sodium. This provides more evidence of impaired ionic regulation in dystrophic muscle and could be used as an index for the evaluation in vivo of therapeutic interventions such as myoblast transfer or gene replacement therapy.

Adenosine Triphosphate↗
PubMed1992

Human muscle cell denervation: the results of a 31-phosphorus magnetic resonance spectroscopy study.

The results presented here demonstrate that there is a major abnormality of high and low energy phosphate metabolism in muscle following peripheral nerve damage. Using 31-phosphorus magnetic resonance spectroscopy the changes in phosphocreatine, adenosine triphosphate, inorganic phosphate and metabolites of membrane metabolism could be observed in vivo in human subjects. The data indicate that there may be a metabolic myopathy in the muscle cells after nerve injury. Further, the metabolic changes did not always return to the control level, indicating a persistence of the abnormality. This failure of the metabolic function of the cells may be important in determining the ultimate outcome of peripheral nerve surgery.

Adenosine Triphosphatases↗
PubMed1992

Proton efflux from rat skeletal muscle in vivo: changes in hypertension.

1. An analysis of the recovery kinetics of intracellular pH and phosphocreatine concentration after exercise in skeletal muscle was developed to calculate the rate of proton efflux in vivo. 2. Recovery of rat leg muscle pH after sciatic nerve stimulation was faster in spontaneously hypertensive rats than in Wistar-Kyoto controls (both n = 5). 3. Analysis of these data showed that the rate of proton efflux depends on intracellular pH, being greater at lower pH. 4. The early rate of proton efflux was greater in spontaneously hypertensive rats [measured over the first 0.8 min, 12.5 mmol min-1 kg-1 (SEM 1.8) in spontaneously hypertensive rats compared with 7.6 mmol min-1 kg-1 (SEM 0.4) in Wistar-Kyoto rats, P less than 0.05], even though pH at the start of recovery was higher [6.30 (SEM 0.03) in spontaneously hypertensive rats compared with 6.17 (SEM 0.01) in Wistar-Kyoto rats, P less than 0.01]. 5. This novel analysis provides a quantitative estimate of the rate of proton efflux in vivo, and demonstrates directly that this is increased in spontaneously hypertensive rats, as has previously been inferred from pH changes during exercise and studies of cultured muscle cells in vitro.

Animals↗
PubMed1992

Effect of bicarbonate administration on skeletal muscle intracellular pH in the rat: implications for acute administration of bicarbonate in man.

1. The effect of bicarbonate administration on the intracellular pH of rat skeletal muscle was examined by using 31P n.m.r. 2. Bicarbonate administered intraperitoneally caused a significant intracellular acidosis in rat skeletal muscle in vivo. When the bicarbonate was administered intravenously there was no such change in the pH of the skeletal muscle. 3. Bicarbonate administration by either route resulted in an elevated mixed venous partial pressure of carbon dioxide and an elevated arterial pH, but no significant change in the arterial partial pressure of carbon dioxide. The increase in arterial bicarbonate concentration after intraperitoneal injection of bicarbonate was delayed when compared with that after intravenous injection. 4. The administration of hypertonic solutions intravenously caused a transient 40-50% fall in blood pressure, which had resolved within 1 min. 5. The data suggest that the effect of bicarbonate administration on intracellular pH in vivo is related not only to carbon dioxide loading of the cell but also to the rate of change in the extracellular bicarbonate concentration.

Animals↗
PubMed1992

Control, bioenergetics, and adaptation in health and disease: noninvasive biochemistry from nuclear magnetic resonance.

The noninvasive study of cellular homeostasis, control, and energetics in tissues and organs within intact living systems is now possible. Nuclear magnetic resonance (NMR) spectroscopy in vivo provides information about key metabolites, reaction rates, the control of ionic equilibria and fluxes (including that of H+), and molecular diffusion and motions within the cell. When phosphorus (31P) is measured, the processes associated with the production and utilization of adenosine triphosphate (ATP) are followed. Using 13C for measurement, the pathways and fluxes in the synthesis and degradation of sugars (e.g., glycogen), amino acids, etc., can be observed. Intracellular, cytoplasmic pH (H+ concentration) can be determined from the 31P-NMR spectrum of organs and cells whereas Na+ and K+ (or its congener Rb+) are directly measurable by NMR. All these can be observed in physiological situations in almost any organism in the animal or plant kingdom. The bioenergetics of locust muscle in flight is as readily measured as that in human muscle in health, training, and disease. When spatially resolved, the NMR spectra can provide metabolic maps of the human heart, brain, and other organs. Thus we can now directly delineate the biochemical basis of human diseases.

Animals↗
PubMed1992

Cellular energetics in hypothyroid muscle.

Skeletal muscle of seven hypothyroid patients was investigated in the resting state and during exercise and recovery using 31P magnetic resonance spectroscopy. The bioenergetics and intracellular pH of the hypothyroid muscle were thus evaluated and compared with results from normal muscle and muscle of patients with mitochondrial myopathy. In resting hypothyroid muscle there were significant elevations in the concentration ratios of phosphocreatine/ATP and inorganic phosphate/ATP, while phosphocreatine/inorganic phosphate and intracellular pH were lower than normal. In exercising hypothyroid muscle, energy stores were depleted more rapidly and acidification began later than in normal muscle. Recovery of phosphocreatine to the pre-exercise value was normal, but intracellular pH recovered slowly. The data suggest that in the hypothyroid state, glycogen breakdown in skeletal muscle was delayed thereby limiting the substrate supply for both glycolytic and oxidative production of ATP at the beginning of exercise. There was no evidence for a decrease in the oxidative capacity of the muscle of our patients, but elevated ADP may have stimulated oxidative metabolism and helped to compensate for low mitochondrial content. The low intracellular pH in resting muscle and the slow pH recovery after exercise imply that proton handling was abnormal in the hypothyroid muscle.

Adult↗
PubMed1992

Bio-energetic changes in human gastrocnemius muscle 1-2 days after strenuous exercise.

[31P]magnetic resonance spectroscopy was used to study the metabolic sequelae of intense muscular activity in gastrocnemius of seven subjects 1-2 days after a 67-mile bicycle ride. The muscle was examined at rest, during a test exercise and during recovery from test exercise. Post-ride and pre-ride results were compared. At rest, the ratio of phosphocreatine to ATP (PCr/ATP) was increased post-ride; during test exercise PCr/(PCr+Pi) was lower post-ride; and the recoveries of PCr, Pi and PCr/(PCr+Pi) after test exercise were delayed, with decreased 'overshoot' of PCr/(PCr+Pi) (which is due to recovery of Pi to below its resting value). Mild mitochondrial damage (perhaps due to exposure to high cytosolic [Pi] during the bicycle ride) may explain some of these results. In contrast to reports of largely eccentric exercise there was no increase in resting Pi/ATP. We have thus demonstrated perturbations of muscle bio-energetics 1-2 days after strenuous exercise, in the absence of convincing enzymological evidence of muscle damage.

Adult↗
PubMed1992

Changes in high-energy phosphates in rat skeletal muscle during acute respiratory acidosis.

We used 31P magnetic resonance spectroscopy to study changes in phosphorus metabolite concentrations in rat skeletal muscle during respiratory acidosis (14 and 20% inspired CO2) and recovery. As intracellular pH fell (from 7.05 to 6.75 after 20 min of 20% CO2), intracellular [P(i)] increased by up to 50% while phosphocreatine concentration decreased by up to 8%. The sum of all intracellular phosphates remained constant. [ADP] decreased by up to 40% in accordance with the creatine kinase equilibrium but the phosphorylation potential [ATP]/([ADP][P(i)]) was preserved as a result of increased [P(i)]. This adjustment may be a mechanism for maintaining mitochondrial ATP synthesis despite low pH. Eventually this increase in cellular [P(i)] could lead to slow efflux of P(i) from the skeletal muscle cell contributing to the hyperphosphataemia of acute respiratory acidosis.

Acidosis, Respiratory↗