scholarly journals The influence of nanomolar calcium ions and physiological levels of thyroid hormone on oxidative phosphorylation in rat liver mitochondria. A possible signal amplification control mechanism

1987 ◽  
Vol 247 (2) ◽  
pp. 315-320 ◽  
Author(s):  
W E Thomas ◽  
A Crespo-Armas ◽  
J Mowbray
Keyword(s):  
Calcium Ions ◽  
Signal Amplification ◽  
Control Mechanism ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Binding Studies ◽  
Receptor Sites ◽  
Low Concentrations ◽  
Hormone Effect

Using different conditions mitochondria from hypothyroid rats can show both unchanged ADP/O ratios and lowered ADP/O ratios without evidence of uncoupling when compared with euthyroid controls. Raising the free Ca2+ concentration to around 25 nM progressively lowered the ADP/O ratio in hypothyroid but not in euthyroid mitochondria. Ruthenium Red did not alter this behaviour and further increasing the Ca2+ concentration to levels below those which stimulate State 3 respiration had no additional effect. Measurements of the free Ca2+ concentration in the mitochondrial suspending medium using a Quin 2 fluorescence assay showed that the mitochondria did not buffer the free Ca2+ at these low concentrations. At 25 nM-free Ca2+, addition of 10-13) M-T3 to hypothyroid mitochondria produced an immediate and significant increase in the ADP/O ratio without altering the free Ca2+ concentration. The hormone effect was maximal by 10(-11) M. The concentration of ATP synthetase can be estimated to lie at about 10 nM in these experiments. Hence it appears possible that a substantial amplification of the hormone signal may have taken place. Comparison with binding studies suggests that T3 may have been maximally stimulating when somewhat less than half its receptor sites had been filled. The possible mechanisms by which this receptor mediated alteration of the ADP/O ratio might be achieved are discussed.

scholarly journals Effects of lysophospholipids on Ca2+ transport in rat liver mitochondria incubated at physiological Ca2+ concentrations in the presence of Mg2+, phosphate and ATP at 37° C

1984 ◽  
Vol 224 (2) ◽  
pp. 423-430 ◽  
Author(s):  
S Dalton ◽  
B P Hughes ◽  
G J Barritt
Keyword(s):  
Plasma Membrane ◽  
Rat Liver ◽  
Isolated Hepatocytes ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Intact Cells ◽  
Phosphate Ions ◽  
Low Concentrations ◽  
Significant Impairment

Lysophospholipids caused the release of 45Ca2+ from isolated rat liver mitochondria incubated at 37 degrees C in the presence of low concentrations of free Ca2+, ATP, Mg2+, and phosphate ions. The concentrations of lysophosphatidylethanolamine, lysophosphatidylcholine, lysophosphatidic acid and lysophosphatidylinositol which gave half-maximal effects were 5, 26, 40 and 56 microM, respectively. The effects of lysophosphatidylethanolamine were not associated with a significant impairment of the integrity of the mitochondria as monitored by measurement of membrane potential and the rate of respiration. Lysophosphatidylethanolamine did not induce the release of Ca2+ from a microsomal fraction, or enhance Ca2+ inflow across the plasma membrane of intact cells, but did release Ca2+ from an homogenate prepared from isolated hepatocytes and incubated under the same conditions as isolated mitochondria. The proportion of mitochondrial 45Ca2+ released by lysophosphatidylethanolamine was not markedly affected by altering the total amount of Ca2+ in the mitochondria, the concentration of extramitochondrial Mg2+, by the addition of Ruthenium Red, or when oleoyl lysophosphatidylethanolamine was employed instead of the palmitoyl derivative. The effects of 5 microM-lysophosphatidylethanolamine were reversed by washing the mitochondria. The possibility that lysophosphatidylethanolamine acts to release Ca2+ from mitochondria in intact hepatocytes following the binding of Ca2+-dependent hormones to the plasma membrane is briefly discussed.

scholarly journals The inhibition of mitochondrial calcium transport by lanthanides and Ruthenium Red

1974 ◽  
Vol 140 (2) ◽  
pp. 143-155 ◽  
Author(s):  
Ken C. Reed ◽  
Fyfe L. Bygrave
Keyword(s):  
Binding Sites ◽  
Calcium Transport ◽  
Specific Binding ◽  
Protein A ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Mitochondrial Calcium ◽  
Binding Studies ◽  
Specific Binding Sites

An EGTA (ethanedioxybis(ethylamine)tetra-acetic acid)-quench technique was developed for measuring initial rates of 45Ca2+ transport by rat liver mitochondria. This method was used in conjunction with studies of Ca2+-stimulated respiration to examine the mechanisms of inhibition of Ca2+ transport by the lanthanides and Ruthenium Red. Ruthenium Red inhibits Ca2+ transport non-competitively with Ki 3×10-8m; there are 0.08nmol of carrier-specific binding sites/mg of protein. The inhibition by La3+ is competitive (Ki=2×10-8m); the concentration of lanthanide-sensitive sites is less than 0.001nmol/mg of protein. A further difference between their modes of action is that lanthanide inhibition diminishes with time whereas that by Ruthenium Red does not. Binding studies showed that both classes of inhibitor bind to a relatively large number of external sites (probably identical with the ‘low-affinity’ Ca2+-binding sites). La3+ competes with Ruthenium Red for most of these sites, but a small fraction of the bound Ruthenium Red (less than 2nmol/mg of protein) is not displaced by La3+. The results are discussed briefly in relation to possible models for a Ca2+ carrier.

scholarly journals Proton translocation by the mitochondrial cytochrome b-c1 complex is inhibited by NN′-dicyclohexylcarbodi-imide

1982 ◽  
Vol 206 (2) ◽  
pp. 419-421 ◽  
Author(s):  
B D Price ◽  
M D Brand
Keyword(s):  
Electron Transport ◽  
Cytochrome Oxidase ◽  
Cytochrome B ◽  
Rat Liver ◽  
Proton Translocation ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Mitochondrial Cytochrome ◽  
Low Concentrations ◽  
Mitochondrial Cytochrome B

NN'-Dicyclohexylcarbodi-imide at low concentrations decreases the H+/2e ratio for rat liver mitochondria over the span succinate to oxygen from 5.9 +/- 0.3 (mean +/- S.E.M.) to 4.0 +/- 0.1 and for the cytochrome b-c1 complex from 3.8 +/- 0.2 to 1.9 +/- 0.1, but has little effect on the H+/2e ratio of cytochrome oxidase. The decrease in stoicheiometry is due, not to uncoupling or inhibition of electron transport, but to inhibition of proton translocation. NN'-Dicyclohexylcarbodi-imide thus ‘decouples’ proton translocation in the cytochrome b-c1 complex.

scholarly journals Effect of micromolar concentrations of manganese ions on calcium-ion cycling in rat liver mitochondria

1983 ◽  
Vol 212 (3) ◽  
pp. 773-782 ◽  
Author(s):  
B P Hughes ◽  
J H Exton
Keyword(s):  
Rat Liver ◽  
Calcium Ion ◽  
Incubation Medium ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Manganese Ions ◽  
Dose Dependent Decrease ◽  
Incubation Temperatures ◽  
Dose Dependent

The effects of micromolar concentrations of Mn2+ on the rat liver mitochondrial Ca2+ cycle were investigated. It was found that the addition of Mn2+ to mitochondria which were cycling 45Ca2+ led to a rapid dose dependent decrease in the concentration of extramitochondrial 45Ca2+ of about 1 nmol/mg of protein. The effect was complete within 30 s, was half maximal with 10 microM Mn2+ and was observed in the presence of 3 mM Mg2+ and 1 mM ATP. It occurred over a broad range of incubation temperatures, pH and mitochondrial Ca2+ loads. It was not observed when either Mg2+ or phosphate was absent from the incubation medium, or in the presence of Ruthenium Red. These findings indicate that micromolar concentrations of Mn2+ stimulate the uptake of Ca2+ by rat liver mitochondria, and provide evidence for an interaction between Mg2+ and Mn2+ in the control of mitochondrial Ca2+ cycling.

Pathway for uncoupler-induced calcium efflux in rat liver mitochondria: inhibition by Ruthenium Red

Biochemistry ◽  
1984 ◽  
Vol 23 (8) ◽  
pp. 1645-1651 ◽  
Author(s):  
Paolo Bernardi ◽  
Venturina Paradisi ◽  
Tullio Pozzan ◽  
Giovanni Felice Azzone
Keyword(s):  
Rat Liver ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Calcium Efflux

scholarly journals Stimulation of the respiration rate of rat liver mitochondria by sub-micromolar concentrations of extramitochondrial Ca2+

1987 ◽  
Vol 245 (1) ◽  
pp. 217-222 ◽  
Author(s):  
J D Johnston ◽  
M D Brand
Keyword(s):  
Respiration Rate ◽  
Rat Liver ◽  
Oxidative Metabolism ◽  
Mitochondrial Respiration ◽  
Liver Mitochondria ◽  
Ruthenium Red ◽  
Rat Liver Mitochondria ◽  
Mitochondrial Matrix ◽  
Stimulation Of

1. The respiration rate of rat liver mitochondria was stimulated by up to 70% when the extramitochondrial Ca2+ concentration was raised from 103 to 820 nM. This occurred when pyruvate, 2-oxoglutarate, or threo-(Ds)-isocitrate was employed as substrate, but not when succinate was used. 2. Ruthenium Red prevented the stimulation of mitochondrial respiration by extramitochondrial Ca2+, showing that the effect required Ca2+ uptake into the mitochondrial matrix. 3. Starvation of rats for 48 h abolished the stimulation of mitochondrial respiration by extramitochondrial Ca2+ when pyruvate was used as substrate, but did not affect the stimulation of 2-oxoglutarate oxidation by extramitochondrial Ca2+. 4. Our findings are in accord with proposals that oxidative metabolism in liver mitochondria may be stimulated by Ca2+ activation of intramitochondrial dehydrogenases.

Sign in / Sign up

Export Citation Format

Share Document