Oxygen conformance of cellular respiration in hepatocytes

1993 ◽  
Vol 265 (4) ◽  
pp. L395-L402 ◽  
Author(s):  
P. T. Schumacker ◽  
N. Chandel ◽  
A. G. Agusti
Keyword(s):  
Metabolic Activity ◽  
Energy Demand ◽  
Lactic Acid Production ◽  
Rat Hepatocytes ◽  
Cellular Respiration ◽  
O2 Uptake ◽  
Rapid Reduction ◽  
Isolated Rat Hepatocytes ◽  
Cell Densities ◽  
O2 Supply

Cellular respiratory rates are normally determined by metabolic activity, but become rate limited by O2 availability if the cell O2 tension (PO2) falls below a critical value (typically 1–10 Torr). An ability to reduce metabolic activity and energy demand in response to a falling O2 availability might confer an increased resistance to a diminished O2 supply. Isolated rat hepatocytes were studied in primary culture under controlled O2 tensions. Cells were obtained by collagenase digestion and seeded into nutritive media in control and experimental spinner flasks at identical cell densities. Cells subjected to rapid reduction in PO2 (100⇢0 Torr over < 40 min) exhibited undiminished O2 uptake until PO2 fell below 10 Torr. By contrast, when cell PO2 was reduced over several hours, significant decreases in O2 uptake became evident at O2 tensions as high as 70 Torr. These decreases were associated with a reduction in ATP concentration and an increase in NAD(P)H, compared with rapidly deoxygenated cells at the same PO2. No loss in cell viability was detected after 24 h at reduced PO2. The decrease in respiratory rate was associated with an increased rate of lactic acid production relative to normoxic controls. Restoration of normoxia was associated with an immediate return of O2 uptake to control levels. These results demonstrate that hepatocytes are capable of reversibly decreasing metabolic activity and O2 demand during sustained moderate reductions in PO2, via a mechanism that appears to involve an inhibition of mitochondrial function other than O2 supply limitation. This response may alter cellular susceptibility to physiological stresses including hypoxia.

Dependence of hepatic gluconeogenesis on PO2: inhibitory effects of halothane

1987 ◽  
Vol 63 (5) ◽  
pp. 1776-1780 ◽  
Author(s):  
F. J. Romero ◽  
F. V. Pallardo ◽  
R. Bolinches ◽  
J. Roma ◽  
G. T. Saez ◽  
...  
Keyword(s):  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Synthesis Rate ◽  
Inhibitory Effects ◽  
O2 Uptake ◽  
Isolated Rat Hepatocytes ◽  
Halothane Concentration ◽  
Low Concentrations ◽  
Glucose Synthesis ◽  
Critical Po2

The dependence of gluconeogenesis and O2 uptake on PO2 in isolated rat hepatocytes is presented. Maintenance of steady-state PO2 was achieved with an oxystat system (Biochem. J. 236: 765–769, 1986). O2 uptake showed a half-maximal (K0.5) value of 0.5 Torr PO2, whereas the glucose synthesis rate was half-maximal at 1.2 Torr PO2. Halothane at concentrations greater than 1 mM exerted a parallel inhibition of O2 uptake and glucose synthesis at all PO2 levels studied. In contrast, at halothane concentrations less than 1 mM, inhibition of glucose synthesis occurred only at less than 20 Torr PO2. At these low concentrations, halothane was without significant effects on cellular O2 uptake. In isolated mitochondria, inhibition of O2 uptake was already half-maximal at a halothane concentration of 0.5 mM. In this subcellular system the inhibitory effect of halothane was independent of PO2. These results demonstrate that the critical PO2 at which cellular O2 utilization begins to decrease and the PO2 at which glucose synthesis begins to decrease are comparable; both PO2 levels are approximately 5 Torr. The metabolic zonation of the liver lobule is discussed in view of the results presented.

scholarly journals The effect of acute ethanol treatment on rates of oxygen uptake, ethanol oxidation and gluconeogenesis in isolated rat hepatocytes

1985 ◽  
Vol 230 (3) ◽  
pp. 595-602 ◽  
Author(s):  
K M Stowell ◽  
K E Crow
Keyword(s):  
Ethanol Oxidation ◽  
Physiological State ◽  
Rat Hepatocytes ◽  
O2 Uptake ◽  
Isolated Rat Hepatocytes ◽  
Liver Preparation ◽  
Acute Ethanol ◽  
Ethanol Pretreatment ◽  
In Cells

In hepatocytes isolated from fed rats, acute ethanol pretreatment (at a dose of 5.0 g/kg body wt.) did not change rates of O2 uptake. In cells from starved animals, acute ethanol pretreatment increased O2 uptake by 17-29%. The increased O2 uptake in hepatocytes from starved rats was not accompanied by increased rates of ethanol oxidation, but was accompanied by increased rates of gluconeogenesis under some conditions. The provision of ethanol (10 mM) as a substrate to cells from fed or starved rats decreased O2 uptake in the absence of other substrates or in the presence of lactate, and increased it in the presence of pyruvate or lactate and pyruvate. The results of this study show that the acute effects of ethanol on liver O2 uptake are dependent on the physiological state of the liver. Previously reported large (2-fold) increases in O2 uptake after acute ethanol pretreatment may have been an artefact owing to low control uptake rates (approximately 1.8 micromol/min per g wet wt. of cells) in the liver preparation used. The ATP contents (2.4-2.6 micromol/g wet wt. of cells) and rates of O2 uptake (2.5-5.0 micromol/min per g wet wt. of cells) of cells used in the present study were the same as values reported under conditions close to those in vivo. Therefore the increase in O2 uptake in cells from starved rats after acute ethanol pretreatment is likely to be of physiological significance.

scholarly journals Effects of fructose concentration on carbohydrate metabolism, heat production and substrate cycling in isolated rat hepatocytes

1979 ◽  
Vol 184 (3) ◽  
pp. 501-507 ◽  
Author(s):  
Dallas G. Clark ◽  
Owen H. Filsell ◽  
David L. Topping
Keyword(s):  
Heat Production ◽  
Rat Hepatocytes ◽  
Fold Increase ◽  
Hepatic Metabolism ◽  
Heat Output ◽  
O2 Consumption ◽  
O2 Uptake ◽  
Isolated Rat Hepatocytes ◽  
High Concentrations ◽  
Fructose 1,6 Bisphosphate

1. Hepatocytes from starved rats were incubated with 5mm-glucose, labelled uniformly with 14C and specifically with 3H at positions 1, 2, 3 or 6, and with fructose at concentrations of 2.5, 7.5 or 25mm. 2. In the absence of other substrates only 1% of the radioactivity initially present in [U-14C]glucose appeared in the metabolic products, CO2, lactate, pyruvate, amino acids and glycogen. 3. Fructose at 2.5mm caused a 30% increase in the glucose concentration and a 4-fold increase in the apparent oxidation of [U-14C]-glucose. 4. The formation of 3H2O from [1-3H]-, [2-3H]-, [3-3H]- or [6-3H]-glucose was 2.4, 4.3, 2.15 or 1.6% respectively in the control incubations and 4.1, 10.4, 7.7 or 5.1% with 2.5mm-fructose. 5. Fructose at 7.5 and 25mm decreased the 3H2O yields to less than the control values, but had no apparent effect on the amount of [U-14C]glucose metabolized. 6. In the incubations with 5mm-glucose and 25mm-fructose there were significant decreases in heat production, O2 consumption and in the ratio of O2 uptake to heat output. 7. Fructose at 2.5mm caused a 64% increase in heat output, but only a 43% increase in O2 uptake. 8. The radioisotopic and calorimetric data demonstrate that physiological concentrations of fructose greatly increase metabolism in hepatocytes from starved rats. These data also indicate increased cycling at glucose/glucose 6-phosphate and at fructose 6-phosphate/fructose 1,6-bisphosphate in the presence of 2.5mm-fructose, although the rates of cycling were actually decreased relative to the amount of glucose catabolized. 9. At concentrations of 2.5, 7.5 and 25mm, fructose depressed hepatocyte ATP concentrations by 20, 65 and 80% respectively. Although fructose at 7.5 and 25mm increased glucose and lactate release, O2 consumption, production of heat and formation of3H2O from [1-3H]-, [2-3H]-, [3-3H]- or [6-3H]-glucose were lowered to values equal to, or less than, controls. These effects probably reflect a severe derangement of hepatic metabolism due to excess phosphorylation of fructose when present at high concentrations.

Cryopreservation of Isolated Rat Hepatocytes: Effects of Iron-Mediated Oxidative Stress on Metabolic Activity

Cryobiology ◽  
1997 ◽  
Vol 34 (2) ◽  
pp. 150-156 ◽  
Author(s):  
Peter De Loecker ◽  
Barry J. Fuller ◽  
Vitali A. Koptelov ◽  
Valentin I. Grischenko ◽  
William De Loecker
Keyword(s):  
Oxidative Stress ◽  
Metabolic Activity ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

scholarly journals Regulation of bioenergetics in O2-limited isolated rat hearts

1994 ◽  
Vol 77 (6) ◽  
pp. 2530-2536 ◽  
Author(s):  
M. Samaja ◽  
S. Casalini ◽  
S. Allibardi ◽  
A. Corno ◽  
S. L. Chierchia
Keyword(s):  
Energy Demand ◽  
Lactate Concentration ◽  
Adaptation To Hypoxia ◽  
O2 Uptake ◽  
Lactate Release ◽  
Rat Hearts ◽  
Perfused Rat Hearts ◽  
Myocardial Contractile ◽  
O2 Supply

Assessing the role of O2 supply in the regulation of cardiac function in O2-limited hearts is crucial to understanding myocardial ischemic preconditioning and adaptation to hypoxia. We exposed isolated Langendorff-perfused rat hearts to either ischemia (low coronary flow) or hypoxemia (low PO2 in the perfusing medium) with matched O2 supply (10% of baseline). Myocardial contractile work and ATP turnover were greater in hypoxemic than in ischemic hearts (P < 0.05; n = 12). Thus, the energy demand was higher during hypoxemia than during ischemia, suggesting that ischemic hearts are more downregulated than hypoxemic hearts. Venous PO2 was 12 +/- 2 and 120 +/- 15 Torr (P < 0.0001) for ischemic and hypoxemic hearts, respectively, but O2 uptake was the same. Lactate release was higher during hypoxemia than during ischemia (9.7 +/- 0.9 vs. 1.4 +/- 0.2 mumol/min, respectively; P < 0.0001). Electrical stimulation (300 min-1; to increase energy demand) increased performance in ischemic (P < 0.005) but not in hypoxemic hearts without changes in venous PO2 or O2 uptake. However, venous lactate concentration and lactate release increased in ischemic (P < 0.002) but not in hypoxemic hearts, suggesting that anaerobic glycolysis provides the energy necessary to meet the increased energy demand in ischemic hearts only. We conclude that high intracellular lactate or H+ concentration during ischemia plays a major role as a downregulating factor. Downregulation disappears in hypoxemic hearts secondary to enhanced washout of lactate or H+.

scholarly journals The application of microcalorimetry to the assessment of metabolic efficiency in isolated rat hepatocytes

1979 ◽  
Vol 180 (3) ◽  
pp. 631-638 ◽  
Author(s):  
Ivan G. Jarrett ◽  
Dallas G. Clark ◽  
Owen H. Filsell ◽  
John W. Harvey ◽  
Michael G. Clark
Keyword(s):  
Liver Cell ◽  
Physiological Saline ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Heat Output ◽  
Metabolic Efficiency ◽  
O2 Uptake ◽  
Isolated Rat Hepatocytes ◽  
Significant Difference ◽  
Isolated Rat

1. Heat output by suspensions of isolated rat hepatocytes was determined by using a modified batch-type microcalorimeter. 2. The ratio of O2 uptake (determined polarographically) to heat output was used to assess the metabolic efficiency of isolated hepatocytes. 3. Cells from starved or fed rats incubated in either bicarbonate-buffered physiological saline containing gelatin, or bicarbonate-buffered physiological saline containing amino acids, serum albumin and glucose showed no significant difference with respect to the ratio of O2 uptake to heat output. 4. For liver cells from 24h-starved rats, the addition of 10mm-dihydroxyacetone and 2.5mm-fructose significantly decreased the ratio of O2 uptake to heat output from 1.94±0.05 in the controls to 1.52±0.04 and 1.54±0.01μmol/J respectively. 5. Glucagon (1μm), which slightly increased both O2 uptake and heat output, did not significantly alter the ratio. 6. The addition of extracellular 10mm-NH4Cl and urease to provide an energetically wasteful cycle by ensuring hydrolysis of newly synthesized urea, lowered the ratio of O2 uptake to heat output from 1.81±0.08 to 1.47±0.06μmol/J, indicating a reduced metabolic efficiency. 7. Metabolic efficiency in rats of different dietary regimen, age and genetically based obesity was also assessed. No differences in the ratio of O2 uptake to heat output were found between liver cell suspensions prepared from rats maintained on colony diet and high-fat diet or sucrose-rich diet nor between animals ranging from 38 to 179 days of age. Comparison of the ratio of liver cell O2 uptake to heat output between homozygote Zucker fa/fa obese rats and their lean littermates showed no significant difference. 8. It is concluded that the ratio of O2 uptake to heat output for isolated hepatocytes is relatively constant unless perturbed by conditions that markedly enhance substrate cycling.

Effect of mitochondrial clustering on O2 supply in hepatocytes

1984 ◽  
Vol 247 (1) ◽  
pp. C83-C89 ◽  
Author(s):  
D. P. Jones
Keyword(s):  
Diffusion Coefficient ◽  
Rat Hepatocytes ◽  
Dependence Analysis ◽  
Isolated Rat Hepatocytes ◽  
Intact Cells ◽  
Isolated Mitochondria ◽  
Intracellular Diffusion ◽  
O2 Supply ◽  
Intermediate Value ◽  
Isolated Rat

Isolated rat hepatocytes were treated with digitonin to selectively disrupt the plasma membrane and allow study of the O2 dependence of mitochondria within the cell cytoskeleton, but without cytosol. Half-maximal oxidation of cytochrome c occurred at 2.0 microM O2 in treated cells incubated under State 3 conditions, whereas in intact cells it was 6.0 microM and in isolated mitochondria (State 3) 0.69 microM. the intermediate value for treated cells indicates that both the geometry of mitochondrial packing and the intracellular diffusion coefficient are important in determining intracellular mitochondrial O2 dependence. Analysis of intracellular diffusion, assuming that the mitochondrial clustering increases the effective mitochondrial radius, indicates that an intracellular diffusion coefficient of between 10(-6) and 4 X 10(-6) cm2 . s-1 and an effective mitochondrial radius of approximately 2 micron would account for the observed intracellular O2 dependence of mitochondrial function.

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