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Biomedical subjects

R S Balaban

Publications and source records attributed to R S Balaban.

At least 163 records · Page 9Linked to original sources
PubMed1983

In vivo flux between phosphocreatine and adenosine triphosphate determined by two-dimensional phosphorous NMR.

The in vivo unidirectional flux between creatine phosphate and ATP was determined in the leg and head of the anesthetized rat using a two-dimensional NMR technique. The unidirectional flux of creatine phosphate to ATP was 13 mumol/s/g-weight in the leg and 2 mumol/s/g-weight in the head. The unidirectional flux between ATP and inorganic phosphate was too slow to be detected and was estimated to be less than 0.1 mumol/s/g-weight.

Adenosine Triphosphate↗
PubMed1983

The efficiency of (Na+ + K+)-ATPase in tumorigenic cells.

The efficiency of (Na+ + K+)-ATPase (i.e. the amount of K+ pumped per ATP hydrolyzed) in intact tumorigenic cells was estimated in this study. This was accomplished by simultaneously measuring the rate of ouabain-sensitive K+ uptake and oxygen consumption in tumorigenic cell suspensions during the reintroduction of K+ to K+-depleted cells. The ATP turnover was then estimated by assuming 5.6-6 ATP/O2 as the stoichiometry of NADH-linked respiration in these cells. In the three cell lines tested (hamster and chick embryo cells transformed with Rous sarcoma virus and Ehrlich ascites cells), the K+/ATP ratio was approximately 2, the same value as that found in normal tissues. Furthermore, only 20% of the total ATP production of these cells was used by (Na+ + K+)-ATPase.

Adenosine Triphosphate↗
PubMed1983

Rates of enzyme-catalyzed exchange determined by two-dimensional NMR: a study of glucose 6-phosphate anomerization and isomerization.

The application of two-dimensional (2D) Fourier-transform NMR to the determination of rate constants of complex enzyme-catalyzed reactions in the steady state is described. The yeast phosphoglucose isomerase (EC 5.3.1.9)-catalyzed anomerization of glucose 6-phosphate (Glc-6-P) as well as its isomerization to fructose 6-phosphate (Fru-6-P) was chosen as an example. The 2D technique permitted the simultaneous monitoring of the time course of the anomerization and isomerization steps, from which the various reaction rates were determined. The results obtained in the steady state demonstrate the usefulness of the 2D technique by confirming that the anomerization of Glc-6-P is enzyme catalyzed and that the isomerization of the alpha anomer of Glc-6-P to Fru-6-P is at least 10 times faster than the isomerization of the beta anomer of Glc-6-P. These results are compared with reaction rates obtained by rapid-quench methods and the mechanistic implications are discussed. Extrapolation of these results suggests that the 2D Fourier-transform NMR method should be applicable in intact biological tissues.

Fourier Analysis↗
PubMed1983

Energy metabolism of preimplantation mammalian blastocysts.

We have measured the relative contributions of glycolytic and oxidative energy production pathways of metabolism in rabbit and mouse preimplantation blastocysts. We have further studied the relationship between these pathways and active transepithelial Na+ transport. Our results show that over 85% of all ATP production arises from mitochondrial respiration. By using amphotericin B to increase the Na+ permeability of the apical (or uterine-facing) membrane of the blastocyst, we have determined that the ratio of ouabain-sensitive Na+ influx to ATP consumption is 3. Based on the measurements of ouabain-sensitive Na+ influx across blastocysts incubated in glucose-containing medium, only 6% of the total energy consumption of the embryo is used for active transepithelial Na+ transport.

Adenosine Triphosphate↗
PubMed1983

Nitrogen-14 nuclear magnetic resonance spectroscopy of mammalian tissues.

The use of 14N nuclear magnetic resonance (NMR) to monitor the concentrations of nitrogenous compounds in biological tissues was investigated. 14N-NMR spectra were collected in vivo and in vitro from several tissues of the rat and rabbit. Many nitrogen-containing compounds were detected, including urea, NH+4, trimethylamines, and several amino acids. In general, the compounds detected had approximately tetrahedral symmetry about the 14N nucleus and concentrations in the millimolar range. A problem that may limit the usefulness of 14N-NMR in intact tissue is the rapid exchange of nitrogen compounds in solution with those bound to sites on macromolecules. Such interactions tend to broaden the 14N resonance signal considerably. The binding of urea to intra- and extracellular proteins is presented as a specific example of this phenomenon. A particularly interesting finding was the high concentration (approximately 90 mM) of trimethylamine compounds in the renal inner medulla. We propose that 14N-NMR is a potentially useful technique for noninvasive detection of specific nitrogen-containing compounds in intact biological tissues.

Amino Acids↗
PubMed1983

Comparison of energy metabolism in human normal and neoplastic (Burkitt's lymphoma) lymphoid cells.

In order to detect possible differences in the energy metabolism between normal and neoplastic lymphoid cells, we studied purified normal human lymphocytes (FL) and transformed lymphoblastoid cell lines derived from umbilical cord blood (CL) and compared them to cell lines derived from American Burkitt's lymphoma (BL). The total adenosine triphosphate production rate by these cells was estimated by measuring O2 consumption and lactic acid production rates. O2 consumption (nmol/min/mg protein) was 4.9 +/- 0.3 (S.D.) in CL, 4.4 +/- 0.3 in FL, and 4.9 +/- 0.3 in BL. Lactic acid production (nmol/min/mg protein) was 30.9 +/- 3.0 in CL, 29.9 +/- 3.0 in FL, and 23.4 +/- 4.0 in BL. Using these values of O2 consumption and lactic acid production, the average adenosine triphosphate production rates (nmol/min/mg protein) were calculated to be 60 in CL, 56 in FL, and 53 in BL. We conclude that the BL do not have more aerobic glycolysis than do normal lymphoid cells, suggesting that the lactic acidosis seen in American Burkitt's lymphoma is not due to a preferential glycolytic metabolism of the tumor. More likely, the lactic acidosis is simply due to the large total mass of these neoplastic cells and not due to a modification of their energy metabolism.

Adenosine Triphosphate↗
PubMed1982

Hormone-induced changes in NADH fluorescence and O2 consumption of rat hepatocytes.

Hepatocytes isolated from fasted male rats were incubated with a mixture of glucose, ribose, mannose, glycerol, and acetate and then treated with vasopressin (ADH), glucagon, or vasoactive intestinal polypeptide (VIP). Each of these hormones causes a rapid transient increase in the fluorescence signal arising from NADH and a sustained increase in the rate of metabolic oxygen consumption (QO2). The NADH transient was largest in response to glucagon, followed by ADH and VIP, respectively. For each hormone the responses were prevented by addition of a calcium-chelating agent. These results show that a transient, Ca2+-dependent redox shift in NADH and stimulation of QO2, perhaps resulting from an increase in the rate of delivery of reducing equivalents to the mitochondrion, occur early in the sequence of events by which several hormones that increase gluconeogenesis act.

Animals↗
PubMed1982

Redox state of cytochrome aa3 in isolated perfused rat kidney.

Optical spectroscopy was used to evaluate mitochondrial anoxia in the isolated perfused rat kidney by determining the percentage of cytochrome aa3 in the reduced state. Despite high levels of plasma flow (greater than 20 ml . g-1 . min-1) and venous PO2 (greater than 300 mmHg), 25--40% of cytochrome aa3 appeared to be in its reduced form. Agents that alter metabolism or transport primarily in renal cortex had little or no effect on the redox state of cytochrome aa3. These included 3-mercaptopicolinate, an inhibitor of gluconeogenesis; 2-tetradecylglycidic acid, an inhibitor of fat metabolism via carnitine-fatty acyltransferase, and acetazolamide. In contrast, a decrease in medullary transport induced by the loop diuretics bumetanide or furosemide produced an increase in cytochrome aa3 oxidation consistent with a decrease in transport-related oxygen consumption in the hypoxic area. The results suggest that substantial portions of the kidney, particularly in the renal medulla, may normally operate on the brink of anoxia despite high PO2 in artery and vein.

Animals↗
PubMed1982

Nuclear magnetic resonance studies of epithelial metabolism and function.

Nuclear magnetic resonance (NMR) is a noninvasive technique for studying cellular metabolism and function. In this review the general applications and advantages of NMR will be discussed with specific reference to epithelial tissues. Phosphorus NMR investigations have been performed on epithelial tissues in vivo and in vitro; however, other detectable nuclei have not been utilized to date. Several new applications of phosphorus NMR to epithelial tissues are also discussed, including studies on isolated renal tubules and sheet epithelia.

Adenosine Diphosphate↗
PubMed1981

Mitochondrial respiratory capacity and Na+- and K+-dependent adenosine triphosphatase-mediated ion transport in the intact renal cell.

Cellular oxygen consumption was monitored during stimulation and inhibition of the Na+- and K+-dependent adenosine triphosphatase in a suspension of intact tubules isolated from the rabbit renal cortex. Respiratory rates were compared to the ADP-stimulated respiratory rate (state 3 rate) obtained in mitochondria released directly from the renal tubules by digitonin shock. At 37 degrees C, in the presence of NADH-linked substrates and fats, isolated renal cells respire at 50 to 60% of the state 3 rate. Inhibition of the (Na+,K+)-ATPase with the cardiac glycoside, ouabain, results in a decline in respiration to 25 to 30% of the state 3 rate. Stimulation of the (Na+,K+)-ATPase produced as a result of nystatin-mediated dissipation of plasma membrane Na+ and K+ gradients results in increased respiration with an oxygen consumption rate characteristic of optimal ATP synthesis (state 3). The relationship between metabolic substrate regimen, mitochondrial respiratory capacity, and cellular energy demand is examined in the context of these findings.

Animals↗
PubMed1981

Phosphorus nuclear magnetic resonance study of the rat kidney in vivo.

We show that phosphorus nuclear magnetic resonance (31P-NMR) can be used to study the metabolic state of kidneys in live, anesthetized rats without the need for surgery. To localize signals from the kidney, we used a radiofrequency surface coil in conjunction with the magnetic field profiling technique that is used for "topical magnetic resonance," (TMR). Signals are observed from phosphorus-containing metabolites including ATP and inorganic phosphate, and under certain conditions intracellular pH can be estimated. We suggest that the ratio of free ATP to free ADP is higher than the estimates of 1.5 to 2.0 obtained from freeze-clamping studies. Because of the important roles that ATP, ADP, inorganic phosphate, and pH are believed to play in cellular metabolism, it seems that 31P-NMR could be a powerful clinical tool.

Adenosine Triphosphate↗
PubMed1981

Microfluorometric monitoring of NAD redox state in isolated perfused renal tubules.

We report the successful application of microfluorometric techniques to monitor the redox state of mitochondrial nicotinamide adenine dinucleotide (NAD) in conjunction with measurements of transepithelial transport in intact isolated perfused tubules from the rabbit kidney. The determination of the redox state of NAD yields important information on the delivery of substrate to, and the energy demands on, the tubular mitochondria. These studies required only minor modifications of the basic perfusion apparatus. With this technique we detected net reductions of mitochondrial NAD upon the addition of metabolic substrates (succinate), the inhibition of active ion transport (ouabain), and the inhibition of mitochondrial electron flow (cyanide). Uncoupling of oxidative phosphorylation with 1799 caused an oxidation of NAD. These changes in NAD redox state are predictable from previous studies in isolated mitochondria, intact tissues, and from experiments on cortical tubule suspensions from the rabbit cortex.

Animals↗
PubMed1981

Stoichiometry and coupling of active transport to oxidative metabolism in epithelial tissues.

A linear relationship has been observed between the rate of active ion transport and the oxygen consumption or lactate production rate in a variety of epithelia. Stoichiometries of ions transported per oxygen consumed or ATP utilized calculated from these relationships reflect actual properties of the active transport step when the following two conditions are met: 1) the basal metabolic rate, obtained in the absence of active transport, remains constant at all rates of active transport; and 2) all the net transport across the tissue considered in the calculation traverses through active (energy-dissipative) pathways. The nature of the cellular mechanism linking active transport and energy production is a fundamental physiological question. Experimental alterations in the rate of active transport elicit mitochondrial state transitions and/or changes in adenine nucleotide concentrations in various epithelia. These findings, obtained by optical and biochemical methods, indicate that ATP and its hydrolysis products constitute part of the coupling mechanism linking the turnover of transport ATPase and the aerobic metabolic rate in epithelia.

Adenosine Triphosphate↗
PubMed1981

Spectrophotometric monitoring of O2 delivery to the exposed rat kidney.

Optical spectrophotometry was used to measure changes in the oxidation-reduction state of cytochrome c oxidase in the in situ rat kidney. Alterations in the redox state of cytochrome c oxidase were monitored during variations in the amount of oxygen being delivered to the animal. Spectral analyses were performed on whole kidney, cortical tubule suspensions, and blood (the latter flowing freely through surgically implanted femoral arteriovenous shunts). Reaction spectra identified the location of the absorption maxima for reduced cytochrome c oxidase to be at approx. 605 nm. Additional spectral analysis indicated that hemoglobin oxygenation-deoxygenation changes had minimal artifactual interference on the cytochrome redox signals. The present results indicate that mitochondrial cytochrome c oxidase is not maximally oxidized in the in situ kidney of anesthetized rats at arterial oxygen in the in situ kidney of anesthetized rats at arterial oxygen tensions within the normal physiological range. The redox state of the enzyme in vivo is altered by changes in the level of inspired oxygen over a wide range. The current data are consistent with the existence of nonuniform regions of aerobic respiration occurring in the in situ kidney.

Aerobiosis↗
PubMed1980

Oxygen consumption and cellular ion transport: evidence for adenosine triphosphate to O2 ratio near 6 in intact cell.

Oxygen (O2) consumption and net K+ uptake were measured simultaneously upon reintroduction of K+ into a K+-depleted suspension of renal tubules. The K+/O2 stoichiometries of 11.8 +/- 0.2 and 8.4 +/- 0.6 were obtained for reduced nicotinamide adenine dinucleotide- and flavoprotein-linked substrates, respectively. These values complement classical K+ to adenosine triphosphate (ATP) and ATP/O2 stoichiometries, thereby demonstrating a remarkably efficient coupling between the processes of Na+- and K+-dependent adenosinetriphosphatase-mediated ion transport and oxidative phosphorylation within the intact cell.

Adenosine Triphosphate↗