Activity Of Rat Liver Mitochondria Research Articles

Effect of VBIT-4 on the functional activity of isolated mitochondria and cell viability

VBIT-4 is a new inhibitor of the oligomerization of VDAC proteins of the outer mitochondrial membrane preventing the development of oxidative stress, mitochondrial dysfunction, and cell death in various pathologies. However, as a VDAC inhibitor, VBIT-4 may itself cause mitochondrial dysfunction in healthy cells. The article examines the effect of VBIT-4 on the functional activity of rat liver mitochondria and cell cultures. We have demonstrated that high concentrations of VBIT-4 (15–30 μM) suppressed mitochondrial respiration in state 3 and 3UDNP driven by substrates of complex I and II. VBIT-4 induced depolarization of organelles fueled by substrates of complex I but not complex II of the respiratory chain. VBIT-4 has been found to inhibit the activity of complexes I, III, and IV of the respiratory chain. Molecular docking demonstrated that VBIT-4 interacts with the rotenone-binding site in complex I with similar affinity. 15–30 μM VBIT-4 caused an increase in H2O2 production in mitochondria, decreased the Ca2+ retention capacity, but increased the time of Ca2+-dependent mitochondrial swelling. We have found that the incubation of breast adenocarcinoma (MCF-7) with 30 μM VBIT-4 for 48 h led to the decrease of the mitochondrial membrane potential, an increase in ROS production and death of MCF-7 cells. The mechanism of action of VBIT-4 on mitochondria and cells is discussed.

Effect of Graphene Oxide and Ammonia-modified Graphene Oxide Particles on ATPase Activity of Rat Liver Mitochondria

Graphene and its derivatives have become promising materials for biomedical applications in the last decade. Before their widespread application, however, evaluating their toxicity and mechanisms underlying interactions with cellular components is imperative. Aims: Assessment of the effect of two graphene derivatives, pristine graphene oxide (GO) and ammonia-modified GO (GO-NH2) particles, on the ATPase activity of rat liver mitochondria and ROS production. Methods: Liver mitochondria were isolated from male albino rats and treated with different concentrations of GO and GO-NH2 particles (4, 10, 25, and 50 μg/ml). ATPase activity of both, intact and uncoupled by freezing/thawing mitochondria was determined by the measurement of inorganic phosphate (Pi) released from ATP. The generation of hydrogen peroxide (H2O2) after exposure of mitochondria to GO and GO-NH2 particles was determined by a DCFH-D assay. Results: GO and GO-NH2 particles applied at concentrations of 4 and 50 μg/ml did not affect the ATPase activity of intact mitochondria. In contrast, in uncoupled mitochondria, they demonstrated a stimulating effect on ATPase activity. The impact of GO-NH2 was more substantial and concentration-dependent. ROS production was also higher in GO-NH2-treated mitochondria. Conclusion: The present study demonstrated that GO and GO-NH2 particles can exert a cytotoxic effect on mitochondria even after a short-time of exposure to both types of particles.

Physiological changes of mitochondria under the diabetes condition and pharmacological approaches to eliminate them

The state of lipid peroxidation (LPO), respiration and oxidative phosphorylation, mitochondrial permeability transition pore (mPTP), and the antiradical activity of rat liver mitochondria in the streptozotocin (STZ)-induced diabetes condition were studied with the consideration of the ways of correcting detected membrane damages using gossitan isolated from the cotton plant Gossypium hirsutum L. It was shown that the rate of respiration of liver mitochondria in states V3 and V4 increases during STZ-induced diabetes, which significantly reduces the respiratory control (RC) and ADP/O coefficients in comparison with the control. The findings suggest that the uncoupling of respiration and oxidative phosphorylation takes place during STZ-induced diabetes. It was shown that in the STZ-induced diabetes condition, the rate of swelling of rat liver mitochondria is higher than that of the healthy ones; this means that mPTP of rat liver mitochondria is in the open state. Gossitan recovers mPTP to the normal condition, thereby removing the STZ effect on mitochondria. Gossitan (a personal dose is 10 mg/kg of body weight, during 8 days) eliminates the detected functional disorders of rat liver mitochondria, probably due to its antioxidant properties.

PHYSIOLOGICAL ALTERATIONS OF MITOCHONDRIA UNDER DIABETES CONDITION AND ITS CORRECTION BY POLYPHENOL GOSSITAN

The state of lipid peroxidation (LPO), respiration and oxidative phosphorylation, mitochondrial permeability transition pore (mPTP) and antiradical activity of rat liver mitochondria in streptozotocin (STZ)-induced diabetes condition were studied, considered the ways of correction of detected membrane damages with the use of gossitan, isolated from cotton plant Gossypium hirsutum L. It was shown that the rate of respiration of liver mitochondria in states V3 and V4 increases during STZ-induced diabetes, which significantly reduces the respiratory control (RC) and ADP/O coefficients in comparison with the control. The findings suggest that the uncoupling of respiration and oxidative phosphorylation takes place during STZ-induced diabetes. It was shown that in the conditions of STZ-induced diabetes, the rate of swelling of rat liver mitochondria is higher than of the healthy ones; this means that mPTP of rat liver mitochondria is in the open state. Gossitan recovers mPTP to the normal condition, thereby removing the effect of STZ on mitochondria. Gossitan (per os dose is 10 mg/kg of body weight, during 8 days) eliminates the detected functional disorders of rat liver mitochondria, probably due to its antioxidant properties.

Structural and functional changes in rat liver mitochondria under calcium ion loading in the absence and presence of flavonoids

The aim of the present work was to elucidate the mechanisms of calcium ion-induced impairments of the ultrastructure and functional activity of isolated rat liver mitochondria in the absence and presence of a number of flavonoids in vitro. In the presence of exogenous Ca²⁺ (20-60 μM), mitochondrial heterogeneity in size and electron density markedly increased: most organelles demonstrated a swollen electron-light matrix, bigger size, elongated cristae and a reduced their number, a damaged native structure of the inner membrane up to its detachment, and some mitochondria showed a more electron-dense matrix (condensed mitochondria). The calcium-induced opening of the mitochondrial permeability transition pores (MPTP) resulted in the ultrastructural disturbances and in the effective inhibition of the respiratory activity of rat liver mitochondria. The flavonoids (10-25 μM) naringenin and catechin, dose-dependently inhibited the respiratory activity of mitochondria and stimulated the MPTP opening in the presence of Ca²⁺ ions. Since Ruthenium red, an inhibitor of the mitochondrial Ca²⁺ uniporter, effectively prevented Ca²⁺-induced MPTP opening both in the absence and presence of flavonoids, we hypothesized that the effect of flavonoids on the MPTP opening could be mediated by stimulation of the Ca²⁺ uniporter.

Fractions of Adenopus breviflorus Extract Modulate Calcium-induced Mitochondrial Permeability Transition Pore Opening in Rat Liver

Abstract Mitochondrial dysfunction (MD) and impaired apoptotic pathways cause irreversible opening of the Mitochondrial Permeability Transition (MPT) pore, resulting in several pathological conditions e.g. cancer, ageing and neurodegenerative diseases. Many bioactive compounds from plants have been identified as modulators of the MPT pore which makes them possible drugs for the management of MD associated diseases. Adenopus breviflorus (A.breviflorus) is a tropical medicinal plant used in folkore medicine as an abortifacient and in treating gonorrhoea. In this study, the effects of ethylacetate and methanol fractions of A.breviflorus were assessed on rat liver MPT pore and Mitochondrial ATPase (mATPase). The fruit of A.breviflorus was extracted with water to obtain the aqueous Extract (AEAB), which was fractionated using vacuum liquid chromatography (VLC) to obtain ethylacetate and methanol fractions of A.breviflorus (EFAB, and MFAB). The extent of MPT pore opening and mATPase by EFAB and MFAB were assayed spectrophotometrically. The results obtained showed that EFAB and MFAB have no significant inductive effect on the MPT pore in the absence of Ca2+. However, in the presence of Ca2+, EFAB inhibited calcium-induced MPT pore opening in a non-concentration dependent manner. Maximum inhibition of MPT pore opening was 57.1% at 50 μg/ml. Interestingly, MFAB potentiated calcium ion effect by opening the pore further. Specifically, MFAB opened the MPT pore by 11, 10, 17 and 9% at 50, 150, 250 and 350 μg/ml, respectively. Furthermore, EFAB and MFAB inhibited mATPase activity in rat liver mitochondria at 62.5, 187.5, 312.5 and 437.5 μg/ml by 2.6, 18.8, 37.3, 52.6% and 41.8, 6.8, 24.3, 8.4%, respectively. The ethylacetate and methanol fractions of Adenopus breviflorus possess potential phytochemicals that can modulate opening of the mitochondrial permeability transition pore and inhibit mitochondrial ATPase activity in rat liver. These fractions may find use in drug development against diseases where excessive apoptosis takes place.

Corrections by melatonin of liver mitochondrial disorders under diabetes and acute intoxication in rats

The aim of the present work was to investigate the mechanisms of oxidative damage of the liver mitochondria under diabetes and intoxication in rats as well as to evaluate the possibility of corrections of mitochondrial disorders by pharmacological doses of melatonin. The experimental (30 days) streptozotocin-induced diabetes mellitus caused a significant damage of the respiratory activity in rat liver mitochondria. In the case of succinate as a respiratory substrate, the ADP-stimulated respiration rate V₃ considerably decreased (by 25%, p < 0·05) as well as the acceptor control ratio (ACR) V₃/V₂ markedly diminished (by 25%, p < 0·01). We observed a decrease of the ADP-stimulated respiration rate V₃ by 35% (p < 0·05), with glutamate as substrate. In this case, ACR also decreased (by 20%, p < 0·05). Surprisingly, the phosphorylation coefficient ADP/O did not change under diabetic liver damage. Acute rat carbon tetrachloride-induced intoxication resulted in considerable decrease of the phosphorylation coefficient because of uncoupling of the oxidation and phosphorylation processes in the liver mitochondria. The melatonin administration during diabetes (10 mg·kg⁻¹ body weight, 30 days, daily) showed a considerable protective effect on the liver mitochondrial function, reversing the decreased respiration rate V₃ and the diminished ACR to the control values both for succinate-dependent respiration and for glutamate-dependent respiration. The melatonin administration to intoxicated animals (10 mg·kg⁻¹ body weight, three times) partially increased the rate of succinate-dependent respiration coupled with phosphorylation. The impairment of mitochondrial respiratory plays a key role in the development of liver injury under diabetes and intoxication. Melatonin might be considered as an effector that regulates the mitochondrial function under diabetes.

The effect of tris buffers on rat liver mitochondrial monoamine oxidase.

The effect of tris buffers upon the monoamine oxidase (MAO) activity in rat liver mitochondria has been investigated. Tris buffer was shown to inhibit MAO in a non-competitive manner with a Ki of 15-25 mM. Tyramine, 5-hydroxytryptamine and beta-phenethylamine but not benzylamine oxidations were all inhibited by tris buffer. All inhibitions, except that of 5-HT, were completely reversible. It is suggested that these effects are produced by conformational changes in the structure of the MAO. The significance of these results is discussed with respect to the use of tris buffers in the extraction and estimation of the activity of MAO.

Acute Toxicity, Antidepressive and Mao Inhibitory Activity of Mangiferin Isolated from Hypericum Aucheri

ABSTRACTAntidepressive effect of mangiferin isolated from Hypericum aucheri Jaub. et Spach (Clusiaceae) was studied. The purpose of this research was to assess the effects of mangiferin in the forced swimming test (FST) and to investigate whether inhibition of monoamine oxidase (MAO) activity contributes to the antidepressant-like effects of mangiferin. Acute toxicity of mangiferin was determined in male mice after p.o. (4984 mg/kg b.w.) and i.p. (490 mg/kg b.w.) administration. Single (dose ranging between 62.5 and 500 mg/kg b.w.) and repeated (250 mg/kg for 7 or 14 days) per oral treatment of mice with mangiferin decreased the immobilization time in FST. The antidepressant activity of mangiferin increased in a dose-dependent manner up to 250 mg/kg b.w., but no increase was observed thereafter. Mangiferin inhibited MAOA (IC50 is 4.1 × 10−4M) and MAOB (IC50 is ≈ 10−3M) activity in rat liver mitochondria. Our findings demonstrated that mangiferin exerted antidepressant-like effect in behavioral paradigms of despair possibly by modulating brain biogenic amines (norepinephrine and serotonin).

The effect of artichoke (Cynara scolymus L.) extract on respiratory chain system activity in rat liver mitochondria

The effect of artichoke extract on mitochondrial respiratory chain (MRC) activity in isolated rat liver mitochondria (including reaction kinetics) was studied. The effect of the extract on the activity of isolated cytochrome oxidase was also studied. Extract in the range of 0.68-2.72 microg/ml demonstrated potent and concentration-dependent inhibitory activity. Concentrations > or =5.4 microg/ml entirely inhibited MRC activity. The succinate oxidase system (MRC complexes II-IV) was the most potently inhibited, its activity at an extract concentration of 1.36 microg/ml being reduced by 63.3% compared with the control (p < 0.05). The results suggest a complex inhibitory mechanism of the extract. Inhibition of the succinate oxidase system was competitive (K(i) = 0.23 microg/ml), whereas isolated cytochrome oxidase was inhibited noncompetitively (K(i) = 126 microg/ml). The results of this study suggest that the salubrious effects of artichoke extracts may rely in part on the effects of their active compounds on the activity of the mitochondrial respiratory chain system.

Arginase activity in mitochondria – An interfering factor in nitric oxide synthase activity assays

Previously, in tightly controlled studies, using three independent, yet complementary techniques, we refuted the claim that a mitochondrial nitric oxide synthase (mtNOS) isoform exists within pure, rat liver mitochondria (MT). Of those techniques, the NOS-catalyzed [ 14C]- l-arginine to [ 14C]- l-citrulline conversion assay (NOS assay) with MT samples indicated a weak, radioactive signal that was NOS-independent [1]. Aliquots of samples from the NOS assays were then extracted with acetone, separated by high performance thin-layer chromatography (HPTLC) and exposed to autoradiography. Results obtained from these samples showed no radioactive band for l-citrulline. However, a fast-migrating, diffuse, radioactive band was observed in the TLC lanes loaded with MT samples. In this manuscript, we identify and confirm that this radioactive signal in MT samples is due to the arginase-catalyzed conversion of [ 14C]- l-arginine to [ 14C]-urea. The current results, in addition to reconfirming the absence of NOS activity in rat liver MT, also show the need to include arginase inhibitors in studies using MT samples in order to avoid confounding results when using NOS activity assays.

Toxicity assessment of the herbicide metolachlor comparative effects on bacterial and mitochondrial model systems

Metolachlor is one of the most intensively used chloroacetamide herbicides. However, its effects on the environment and on non-target animals and humans as well as its interference at a cell/molecular level have not yet been fully elucidated. The aim of this study was: firstly, to evaluate the potential toxicity of metolachlor at a cell/subcellular level by using two in vitro biological model systems (a strain of Bacillus stearothermophilus and rat liver mitochondria); secondly, to evaluate the relative sensibility of these models to xenobiotics to reinforce their suitability for pollutant toxicity assessment. Our results show that metolachlor inhibits growth and impairs the respiratory activity of B. stearothermophilus at concentrations two to three orders of magnitude higher than those at which bacterial cells are affected by other pesticides. Also at concentrations significantly higher than those of other pesticides, metolachlor depressed the respiratory control ratio, membrane potential and respiration of rat liver mitochondria when malate/glutamate or succinate were used as respiratory substrates. Moreover, metolachlor impaired the respiratory activity of rat liver mitochondria in the same concentration range at which it inhibited bacterial respiratory system (0.4–5.0 μmol/mg of protein). In conclusion, the high concentration range at which metolachlor induces toxicity in vitro suggests that this compound is safer than other pesticides previously studied in our laboratory, using the same model systems. The good parallelism between metolachlor effects on both models and the toxicity data described in the literature, together with results obtained in our laboratory with other compounds, indicate the suitability of these systems to assess toxicity in vitro.

Glycation damage targets glutamate dehydrogenase in the rat liver mitochondrial matrix during aging

Aging is accompanied by gradual cellular dysfunction associated with an accumulation of damaged proteins, particularly via oxidative processes. This cellular dysfunction has been attributed, at least in part, to impairment of mitochondrial function as this organelle is both a major source of oxidants and a target for their damaging effects, which can result in a reduction of energy production, thereby compromising cell function. In the present study, we observed a significant decrease in the respiratory activity of rat liver mitochondria with aging, and an increase in the advanced glycation endproduct-modified protein level in the mitochondrial matrix. Western blot analysis of the glycated protein pattern after 2D electrophoresis revealed that only a restricted set of proteins was modified. Within this set, we identified, by mass spectrometry, proteins connected with the urea cycle, and especially glutamate dehydrogenase, which is markedly modified in older animals. Moreover, mitochondrial matrix extracts exhibited a significant decrease in glutamate dehydrogenase activity and altered allosteric regulation with age. Therefore, the effect of the glycating agent methylglyoxal on glutamate dehydrogenase activity and its allosteric regulation was analyzed. The treated enzyme showed inactivation with time by altering both catalytic properties and allosteric regulation. Altogether, these results showed that advanced glycation endproduct modifications selectively affect mitochondrial matrix proteins, particularly glutamate dehydrogenase, a crucial enzyme at the interface between tricarboxylic acid and urea cycles. Thus, it is proposed that glycated glutamate dehydrogenase could be used as a biomarker of cellular aging. Furthermore, these results suggest a role for such intracellular glycation in age-related dysfunction of mitochondria.

A possible restriction of ferro- and ferricyanide oxidoreductase activities of rat liver mitochondria by the outer membrane

In this work, various ferro-ferricyanide oxidoreductase activities of rat liver mitochondria were studied to find conditions under which the outer membrane might restrict the flux of these highly charged non-biological anions. When the isotonic low ionic strength medium was supplemented with 25 mM KCl, a several-fold increase in the succinate-ferricyanide reductase activity of mitochondria and in the rate of external NADH oxidation in the presence of ferrocyanide was observed. Mitochondrial respiration with 5 mM ferrocyanide was almost completely inhibited after consumption of 3.8–18.5% of the dissolved oxygen, depending on the medium and the presence of 2,4-dinitrophenol. These and other experimental data together with mathematical modeling of the redox-state equilibrium suggest that the measured activities might be restricted by two factors: first, the permeability of the outer mitochondrial membrane and second, a strong influence of the ionic strength of incubation media on the intermembrane space redox reactions.

Starvation-induced posttranscriptional control of rat liver mitochondrial citrate carrier expression

Starvation has been associated with a reduced citrate carrier (CTP) activity in rat liver mitochondria. In the present study the molecular mechanism responsible for this reduction was investigated. Northern blot analysis performed with hepatic total RNA showed a decrease of about 40% in the CTP mRNA abundance in starved rats, when compared to fed animals. Nuclear run-on assay did not reveal any appreciable difference in the rate of CTP mRNA synthesis between the two groups of animals, while the apparent half-life of CTP mRNA in hepatocytes from fed and starved rats was 11 and 6 h, respectively. Therefore, these results suggest that in starved rats the regulation of hepatic CTP expression occurs at posttranscriptional level. Moreover, the reduced CTP activity in starved animals gradually increased by refeeding. The carrier activity reached fed rat values 6–9 h following refeeding. Interestingly, the accumulation of CTP mRNA raised in parallel with the transport activity.

Stimulatory effect of regucalcin on ATP-dependent Ca2+ uptake activity in rat liver mitochondria

The effect of Ca(2+)-binding protein regucalcin on Ca(2+)-ATPase activity in isolated rat liver mitochondria was investigated. The presence of regucalcin (0.1, 0.25, and 0.5 microM) in the enzyme reaction mixture led to a significant increase in Ca(2+)-ATPase activity. Regucalcin significantly stimulated ATP-dependent (45)Ca(2+) uptake by the mitochondria. Ruthenium red (10(-5) M) or lanthanum chloride (10(-4) M), an inhibitor of mitochondrial Ca(2+) uptake, completely inhibited regucalcin (0.25 microM)-increased mitochondrial Ca(2+)-ATPase activity and (45)Ca(2+) uptake. The effect of regucalcin (0.25 microM) in increasing Ca(2+)-ATPase activity was completely inhibited by the presence of digitonin (10(-2)%), a solubilizing reagent of membranous lipids, or vanadate (10(-5) M), an inhibitor of phosphorylation of ATPase. The activatory effect of regucalcin (0.25 microM) on Ca(2+)-ATPase activity was not further enhanced in the presence of dithiothreitol (2.5 mM), a protecting reagent of the sulfhydryl (SH) group of the enzyme, or calmodulin (0.60 microM), a modulator protein of Ca(2+) action that could increase mitochondrial Ca(2+)-ATPase activity. The present study demonstrates that regucalcin can stimulate Ca(2+) pump activity in rat liver mitochondria, and that the protein may act on an active site (SH group)-related to phosphorylation of mitochondrial Ca(2+)-ATPase.

Chronic ethanol consumption causes alterations in the structural integrity of mitochondrial DNA in aged rats.

Chronic ethanol consumption adversely affects the respiratory activity of rat liver mitochondria. It causes increased cellular production of oxygen radical species and selectively decreases mitochondrial glutathione (GSH) levels. Here we show, using Southern hybridization techniques on total rat genomic DNA, that long-term (11-13 months) ethanol feeding, using the Lieber-DeCarli diet, results in a 36% (P <.05; n = 4) decrease in hepatic mitochondrial DNA (mtDNA) levels when compared with paired controls. UV quantitation of mtDNA isolated from hepatic mitochondria showed that chronic ethanol intake (11-13 months) causes a 44% (P <.01; n = 6) decrease in the amount of mtDNA per milligram of mitochondrial protein. No significant decline in mtDNA levels was seen in ethanol-fed animals maintained on the diet for 1 to 5 months. Ethanol feeding caused a 42% (P <.01; n = 4) and a 132% (P <.05; n = 3) increase in 8-hydroxydeoxyguanosine (8-OHdG) formation in mtDNA in animals maintained on the diet for 3 to 6 months and 10 to 11 months, respectively. In addition, agarose gel electrophoresis revealed a 49% increase (P <.05; n = 3) in mtDNA single-strand breaks (SSB) in animals fed ethanol for more than 1 year. These findings suggest that chronic ethanol consumption causes enhanced oxidative damage to mtDNA in older animals along with increased strand breakage, and that this results in its selective removal/degradation by mtDNA repair enzymes.

A specific and rapid method for determination of adenosine 3'-monophosphate (3'-AMP) content and 3'-AMP forming enzyme activity in rat liver mitochondria, using reversed-phase HPLC with fluorescence detection.

To study the physiological significance of adenosine 3'-monophosphate (3'-AMP), an intracellular P-site inhibitor of adenylate cyclase, in rat liver mitochondria, a specific, rapid and reliable assay method for determination of 3'-AMP and the activity of its forming enzyme is required. 3'-AMP in rat liver was determined to be ca. 23+/-7 nmol/g wet weight, but no 2-deoxy-3'-AMP, another P-site inhibitor of adenylate cyclase, was detected, even when using a reversed-phase HPLC column with a fluorescent-reaction, as established in this study. By using the optimized assay method developed here, 3'-AMP forming enzyme activity in rat crude mitochondrial extract was found to be enhanced by EDTA and inhibited by p-chloromercurybenzoate. The optimum pH was ca. 5.8 and no divalent cation was required for activity. From these results, 3'-AMP forming enzyme(s) in rat liver mitochondria could be classified as acid exoribonuclease, which mainly existed in an active form. The results obtained in this study will help to gain more insight into the physiological roles of 3'-AMP in living systems.

Thyroid Hormones Regulate the Onset of Osmotic Activity of Rat Liver Mitochondria after Birth*

The effect of thyroid hormone deprivation on the osmotic activity of liver mitochondria from early newborn rats was studied. Experimentally induced hypothyroidism prevented the increase in the osmotic activity of mitochondria observed immediately after birth. Osmotic activity was restored by T4 and T3 treatment to hypothyroid newborns but not when this treatment was supplemented with cycloheximide. Under the same circumstances, streptomycin had no effect. Hypothyroidism abolished the change in the slope of the osmotic curve (plot of inverse absorbance of mitochondrial suspensions incubated in sucrose solutions vs. inverse sucrose concentration) observed in mitochondria from euthyroid newborns at 110-120 mOsm sucrose, suggesting that hypothyroidism prevents the formation of tight physical connections between mitochondrial outer and inner membranes. Thyroid hormone deprivation increased the passive permeability of the mitochondrial inner membrane to protons, resulting in a decreased respiratory control ratio. Hypothyroidism prevented the sharp decrease in the affinity of mitochondria for ATP observed in euthyroid newborns immediately after birth. These results corroborate our previous suggestion (Endocrinology, 1995, 136:4448) that, during the early neonatal period, thyroid hormones control the synthesis of some nucleus-coded protein(s) involved in the assembly of F0,F1-ATPase.

Thyroid Hormones Regulate the Onset of Osmotic Activity of Rat Liver Mitochondria after Birth

The effect of thyroid hormone deprivation on the osmotic activity of liver mitochondria from early newborn rats was studied. Experimentally induced hypothyroidism prevented the increase in the osmotic activity of mitochondria observed immediately after birth. Osmotic activity was restored by T4 and T3 treatment to hypothyroid newborns but not when this treatment was supplemented with cycloheximide. Under the same circumstances, streptomycin had no effect. Hypothyroidism abolished the change in the slope of the osmotic curve (plot of inverse absorbance of mitochondrial suspensions incubated in sucrose solutions vs. inverse sucrose concentration) observed in mitochondria from euthyroid newborns at 110–120 mOsm sucrose, suggesting that hypothyroidism prevents the formation of tight physical connections between mitochondrial outer and inner membranes. Thyroid hormone deprivation increased the passive permeability of the mitochondrial inner membrane to protons, resulting in a decreased respiratory control ratio. Hypothyroidism prevented the sharp decrease in the affinity of mitochondria for ATP observed in euthyroid newborns immediately after birth. These results corroborate our previous suggestion that, during the early neonatal period, thyroid hormones control the synthesis of some nucleus-coded protein(s) involved in the assembly of F0,F1-ATPase.