scholarly journals The uptake and release of calcium by heart mitochondria

1977 ◽  
Vol 168 (3) ◽  
pp. 447-456 ◽  
Author(s):  
Eric J. Harris
Keyword(s):  
Local Anaesthetics ◽  
Inhibitory Effect ◽  
Heart Mitochondria ◽  
Rate Coefficients ◽  
Mitochondrial Activity ◽  
Low Concentrations ◽  
Spontaneous Action ◽  
Rat Heart Mitochondria ◽  
Kinetics Of Uptake

The kinetics of uptake of Ca2+ by rat heart mitochondria were studied by a spectrophotometric method with Arsenazo III indicator. The exponential rate coefficients measured with or without added phosphate increase with the amount of Ca2+ added up to about 24μm. Evidence is given that the effect is attributable to a combination of formation of chelates at low concentrations to act as Ca2+ buffers, with co-transport of substrate to provide more respiratory fuel. The inhibitory effect of Mg2+ depends on the Ca2+ concentration, so with a constant [Mg2+] the low concentrations of Ca2+ are most inhibited, and the rate coefficients are still more Ca2+-dependent. Ca2+ uptake is slowed by local anaesthetics such as butacaine and dibucaine, and also by propranolol and palmitoyl-CoA. After an uptake, the release of Ca2+ was investigated. The spontaneous release involves an initially slow and small appearance of free Ca2+ and is followed by an auto-accelerated phase. The release is accompanied by a gradual decrease in internal ATP; it is initiated by palmitoyl-CoA (reversed by carnitine), by lysophosphatidylcholine, by Na+ salts (reversed by oligomycin) and by K+ salts added to a K+-free medium containing valinomycin. The process is probably a response to an increased energy load imposed on the mitochondria by the various conditions, which include the spontaneous action of phospholipase activated by traces of Ca2+. The problem of how much mitochondrial activity is participating in normal heart Ca2+ turnover is discussed, and experiments showing only 7–14% exchange of the mitochondrial Ca2+ occurring in vivo in 10 or 20min are reported.

scholarly journals The effect of lead on the calcium-handling capacity of rat heart mitochondria

1976 ◽  
Vol 158 (2) ◽  
pp. 289-294 ◽  
Author(s):  
D R Parr ◽  
E J Harris
Keyword(s):  
Rat Heart ◽  
Heart Tissue ◽  
Calcium Handling ◽  
Primary Effect ◽  
Heart Mitochondria ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Low Concentrations ◽  
Rat Heart Mitochondria

1. Very low concentrations of Pb2+ decrease the capacity of rat heart mitochondria, oxidizing pyruvate plus malate, to remove Ca2+ from the medium. 2. The primary effect is on the rate of Ca2+ sequestration; this is reflected in the overall extent of Ca2+ removal. 3. Pb2+ has at least two separate actions. Below about 0.5 nmol/mg of protein, it acts solely by competing with Ca2+ (Ki = 0.4 muM); above this concentration it also inhibits the production or use of respiratory energy, so that at 1 nmol of Pb2+/mg of protein, Ca2+ removal is almost completely abolished. 4. Pb2+ inhibits coupled and uncoupled respiratory O2 use by mitochondria oxidizing pyruvate plus malate, but at higher concentrations than those that affect Ca2+ removal; similar concentrations of Pb2+ inhibit pyruvate uptake, but not malate uptake, by the mitochondria. 5. Mg2+ only decreases Ca2+ removal by competition, and is a far-less effective competitor than Pb2+ (Ki = 0.15 mM). It is possible that the primary cause of the second effect of Pb2+ is displacement of membrane Mg2+. 6. The consequences of these results are discussed in terms of the possible involvement of heart mitochondria in excitation-contraction coupling, and the Pb2+ levels that might occur in heart tissue in vivo.

Characterization of CDPdiacylglycerol hydrolase in mitochondrial and microsomal fractions from rat lung

1988 ◽  
Vol 66 (5) ◽  
pp. 425-435 ◽  
Author(s):  
Amy Mok ◽  
Tanya Wong ◽  
Octavio Filgueiras ◽  
Paul G. Casola ◽  
Don W. Nicholson ◽  
...  
Keyword(s):  
Divalent Cations ◽  
Mitochondrial Fraction ◽  
Liver Mitochondria ◽  
Inhibitory Effect ◽  
Mitochondrial Activity ◽  
Rat Lung ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Mercuric Ions

CDPdiacylglycerol pyrophosphatase (E. C. 3.6.1.26) activity has been examined in rat lung mitochondrial and microsomal fractions. While the mitochondrial hydrolase exhibited a broad pH optimum from pH 6–8, the microsomal activity decreased rapidly above pH 6.5. Apparent Km values of 36.2 and 23.6 μM and Vmax values of 311 and 197 pmol∙min−1∙mg protein−1 were observed for the mitochondrial and microsomal preparations, respectively. Addition of parachloromercuriphenylsulphonic acid led to a marked inhibition of the microsomal fraction but slightly stimulated the mitochondrial activity at low concentrations. Mercuric ions were inhibitory with both fractions. Although biosynthetic reactions utilizing CDPdiacylglycerol require divalent cations, addition of Mg2+, Mn2+, Ca2+, Zn2+, Co2+, and Cu2+ all inhibited the catabolic CDPdiacylglycerol hydrolase activity in both fractions. EDTA and EGTA also produced an inhibitory effect, especially with the mitochondrial fraction. Although addition of either adenine or cytidine nucleotides led to a decrease in activity with both fractions, the marked susceptibility to AMP previously reported for this enzyme in Escherichia coli membranes, guinea pig brain lysosomes, and pig liver mitochondria was not observed. These results indicate that rat lung mitochondria and microsomes contain specific CDPdiacylglycerol hydrolase activities, which could influence the rate of formation of phosphatidylinositol and phosphatidylglycerol for pulmonary surfactant.

scholarly journals Studies on Analogues of L-Cysteine and L-Cystine

Blood ◽  
1956 ◽  
Vol 11 (1) ◽  
pp. 1-10 ◽  
Author(s):  
AUSTIN S. WEISBERGER ◽  
LEIF G. SUHRLAND ◽  
JOSEPH SEIFTER
Keyword(s):  
Amino Acids ◽  
Spatial Configuration ◽  
Spatial Relationship ◽  
Inhibitory Effect ◽  
Selenium Compounds ◽  
Low Concentrations ◽  
Relationship Of ◽  
Normal Cellular Function

Abstract The amino acids L-cysteine and L-cystine appear to have an important role in the metabolism of leukocytes. Decreased availability of these amino acids may therefore have important effects on leukocytes. The possibility of decreasing the influx of radioactive L-cystine into leukemic leukocytes was investigated by exposing the leukocytes to various analogues of cysteine (cystine) prior to incubation with S35 L-cystine. It was found that a highly specific structural and spatial configuration is required to decrease the influx of S35 L-cystine. Thus unlabeled L-cysteine is effective in decreasing the incorporation of radioactive L-cystine. However, analogues of cystine in which there is modification or substitution of the sulfhydryl, amino or carboxyl group do not decrease the influx of S35 L-cystine. Furthermore, any alteration in the spatial relationship of the sulfhydryl and amino groups of L-cysteine also results in a loss of the ability of an analogue to decrease the incorporation of S35 L-cystine. Of the compounds studied and in the concentrations employed, only unlabeled L-cysteine, selenium cystine and phenyl selenium cysteine were effective. Selenium cystine is identical with cystine except that selenium replaces the sulfur in the molecule. Phenyl selenium cysteine is also closely related structurally to cysteine. The mechanism of action of selenium cystine and phenyl selenium cysteine in decreasing the influx of S35 L-cystine is not known. Other selenium compounds tested were ineffective. These compounds may exert their inhibitory effect by (a) competitive combination with specific intracellular receptors for L-cysteine (L-cystine), (b) inactivation of enzymes or compounds essential for normal cellular function, (c) alteration in membrane permeability or (d) a toxic effect of selenium. Since selenium cystine and phenyl selenium cystine are inhibitory in low concentrations in vitro, these compounds may have important effects on leukemic leukocytes in vivo.

scholarly journals Evidence for Effective Inhibitory Actions on Hyperpolarization-Activated Cation Current Caused by Ganoderma Triterpenoids, the Main Active Constitutents of Ganoderma Spores

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4256 ◽  
Author(s):  
Wei-Ting Chang ◽  
Zi-Han Gao ◽  
Yi-Ching Lo ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Inhibitory Effect ◽  
Firing Frequency ◽  
Gh3 Cells ◽  
Heart Cells ◽  
Excitable Cells ◽  
Cell Current ◽  
Spontaneous Action

The triterpenoid fraction of Ganoderma (Ganoderma triterpenoids, GTs) has been increasingly demonstrated to provide effective antioxidant, neuroprotective or cardioprotective activities. However, whether GTs is capable of perturbing the transmembrane ionic currents existing in electrically excitable cells is not thoroughly investigated. In this study, an attempt was made to study whether GTs could modify hyperpolarization-activated cation currents (Ih) in pituitary tumor (GH3) cells and in HL-1 atrial cardiomyocytes. In whole-cell current recordings, the addition of GTs produced a dose-dependent reduction in the amplitude of Ih in GH3 cells with an IC50 value of 11.7 µg/mL, in combination with a lengthening in activation time constant of the current. GTs (10 µg/mL) also caused a conceivable shift in the steady-state activation curve of Ih along the voltage axis to a more negative potential by approximately 11 mV. Subsequent addition of neither 8-cyclopentyl-1,3-dipropylxanthine nor 8-(p-sulfophenyl)theophylline, still in the presence of GTs, could attenuate GTs-mediated inhibition of Ih. In current-clamp voltage recordings, GTs diminished the firing frequency of spontaneous action potentials in GH3 cells, and it also decreased the amplitude of sag potential in response to hyperpolarizing current stimuli. In murine HL-1 cardiomyocytes, the GTs addition also suppressed the amplitude of Ih effectively. In DPCPX (1 µM)-treated HL-1 cells, the inhibitory effect of GTs on Ih remained efficacious. Collectively, the inhibition of Ih caused by GTs is independent of its possible binding to adenosine receptors and it might have profound influence in electrical behaviors of different types of electrically excitable cells (e.g., pituitary and heart cells) if similar in vitro or in vivo findings occur.

Inhibitors of Tyrosinase

1955 ◽  
Vol 32 (3) ◽  
pp. 468-484
Author(s):  
M. G. M. PRYOR
Keyword(s):  
Methylene Blue ◽  
Dissolved Oxygen ◽  
Inhibitory Effect ◽  
Tyrosinase Activity ◽  
Aromatic Substrate ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Low Concentrations ◽  
Sulphydryl Groups

1. It has been reported that if Drosophila larvae are ground to a fine paste with sand, the homogenate shows little tyrosinase activity, but that if the larvae are allowed to blacken in chloroform vapour before grinding, activity is increased. 2. This has been interpreted as showing the effect of an intracellular inhibitor, set free by rupturing the cells, but destroyed by chloroform. This inhibitor has been identified by previous authors as a dehydrogenase. 3. It is here suggested that the lack of activity of Drosophila extracts prepared with sand is due to destruction of tyrosinase as it oxidizes naturally occurring aromatic substrates. 4. It is shown that tyrosinase is destroyed by oxidizing the aromatic substrate present in the cuticle of Calliphora larvae, or by very low concentrations of homocatechol. 5. The aromatic substrate of Calliphora larvae is concentrated in the cuticle, and would be set free by fine grinding. 6. Drosophila or Calliphora larvae yield a more active extract when ground with sand than when simply crushed, provided that they are tested soon after grinding. 7. The tyrosinase activity of such extracts is not increased by chloroform or methanol. 8. The compound between o-quinones and amino-acids is capable of oxidizing ascorbic acid or excess amino-acid without the aid of an enzyme, and of simultaneously reducing methylene blue. 9. This reaction, rather than the activity of dehydrogenases, is probably responsible for most of the ability of damaged insect tissue to bleach methylene blue. 10. The blood of insects normally contains dissolved oxygen in equilibrium with the air. 11. The reaction involved in the blackening of insect blood may consume all the dissolved oxygen. 12. Previous observations on fluctuations in the oxidation-reduction potential of the blood of Calliphora larvae with age are probably due to changes in the rate at which oxygen is consumed by the blood after it is shed. 13. There does not therefore appear to be any valid evidence that tyrosinase is inhibited in vivo by the action of dehydrogenases. The absence of tyrosinase activity in undamaged tissue is probably due to the structure of the cytoplasm, which keeps enzyme and substrate apart. 14. Instances of the inhibition of tyrosinase reported in Crustacea and Echinodermata seem to be susceptible of the same explanation as in insects. 15. The supposed inhibitory effect of sulphydryl groups reported for vertebrate melanophores is shown to be due to the combination of sulphydryl groups with o-quinones, which prevents the formation of melanins.

The Inhibitory Effect of Tannins on Lipid Peroxidation of Rat Heart Mitochondria

1995 ◽  
Vol 47 (2) ◽  
pp. 138-142 ◽  
Author(s):  
CHUANG-YE HONG ◽  
CHEIN-PING WANG ◽  
SHIANG-SUO HUANG ◽  
FENG-LIN HSU
Keyword(s):  
Lipid Peroxidation ◽  
Rat Heart ◽  
Inhibitory Effect ◽  
Heart Mitochondria ◽  
Rat Heart Mitochondria

SITES OF METYRAPONE INHIBITION OF STEROID BIOSYNTHESIS BY RAT ADRENAL MITOCHONDRIA

1974 ◽  
Vol 76 (4) ◽  
pp. 703-711 ◽  
Author(s):  
Andres Carballeira ◽  
Su Chiau Cheng ◽  
Lawrence M. Fishman
Keyword(s):  
Inhibitory Effect ◽  
Side Chain ◽  
Steroid Biosynthesis ◽  
Side Chain Cleavage ◽  
Chain Cleavage ◽  
Low Concentrations ◽  
Wide Range ◽  
Generating System

ABSTRACT Rat adrenal mitochondrial preparations supplemented with an NADPH-generating system were incubated with various labelled substrates in order to evaluate further the action of metyrapone on the utilization of cholesterol for steroid biosynthesis1). The formation of pregnenolone from [4-14C] cholesterol (0.5, 1.0 and 2.0 μCi) in 5, 10 and 15 min incubations was decreased by 72–82 % in the presence of metyrapone (0.5 mm). Similarly, the generation of labelled side chain fragments from [26-14C]-cholesterol was depressed 36–42 % by 0.2 mm metyrapone and 65–70 % by 1.0 mm inhibitor during 30, 60 and 90 min incubations. Metyrapone inhibition of the side chain cleavage was not observed, however, if cholesterol was replaced as substrate by its C-20 hydroxylated analog: The formation of pregnenolone from [7-3H]20α-hydroxycholesterol (0.5, 1.0 and 2.0 μCi), also an NADPH-mediated mitochondrial reaction, was not affected by similar concentrations of metyrapone, indicating that the inhibition observed with cholesterol as substrate is not related to non-specific toxic effects, to interference with NADPH generation or to impairment of NADPH function in the mitochondrial electron transport system. Parallel incubations with [4-14C] 11-deoxycorticosterone and with [4-14C] cholesterol over a wide range of inhibitor concentrations (0.01–1.0 mm) demonstrated that the effects of metyrapone on 11β-hydroxylation and on the side chain cleavage were dose-related; at low concentrations, however, metyrapone was a more potent inhibitor of 11β-hydroxylation than of cholesterol conversion to pregnenolone. These studies demonstrate clearly in the rat adrenal the dual inhibitory effect of metyrapone sug-gested by previous in vivo and in vitro observations in man.

EFFECT OF COBALT IONS ON MYOCARDIAL METABOLISM

1967 ◽  
Vol 45 (8) ◽  
pp. 1219-1223 ◽  
Author(s):  
G. S. Wiberg ◽  
I. C. Munro ◽  
A. B. Morrison
Keyword(s):  
Oxygen Uptake ◽  
Succinic Dehydrogenase ◽  
Inhibitory Effect ◽  
Cardiac Mitochondria ◽  
Succinic Dehydrogenase Activity ◽  
In Vitro System ◽  
Cobalt Ions ◽  
Rat Heart Mitochondria

Cobalt treatment (4 mg/kg intraperitoneally for 8 days) significantly depressed the oxygen uptake of rat heart mitochondria incubated in pyruvate, octanoate, and stearate media. Cobalt treatment did not, however, affect oxygen uptake in cardiac mitochondria prepared from thiamine-deficient rats. The addition of α-lipoic acid to the in vitro system greatly enhanced the ability of mitochondria from cobalt-treated rats to metabolize pyruvate. Cobalt treatment in vivo did not appear to exert any inhibitory effect on myocardial succinic dehydrogenase activity.

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