Mitochondrial respiration and triiodothyronine concentration in liver from postpubertal and adult rats.

The purpose of this study was to investigate the decline in rat liver mitochondria respiration found in adult rats compared to younger ones, and to find a link between this respiratory impairment and a tissue hypothyroidism state. To this end, hepatic concentration and serum levels of triiodothyronine were measured in postpubertal rats (60 days old) and adult rats (180 days old). In addition, in these rats we measured oxidative phosphorylation in homogenate together with coupled and uncoupled respiration in isolated mitochondria using succinate or durohydroquinone as substrate. We found that mitochondria from adult rats consumed less oxygen compared to younger rats due to lower electron transport chain and phosphorylating system activity. In addition, we found that in state 4 condition, mitochondria from adult rats consumed less oxygen than mitochondria from young rats. Finally, we found a decrease in liver triiodothyronine concentration in adult rats. In conclusion, the results of this study show that hepatic mitochondria in adult rats have a decreased ATP synthesis capacity and proton permeability, both consistent with the tissue hypothyroidism found in the liver of adult rats.     

The effects of magnesium on state 3 respiration of liver mitochondria from control and cold-acclimated rats and hamsters.

1. Increasing the Mg2+ concentration results in a depression of succinoxidase-linked state 3 respiration of liver mitochondria from both control and cold-acclimated rats and hamsters. 2. It appears that in the cold-acclimated hamster, liver mitochondrial respiration is more sensitive to changes in Mg2+ levels than that of the rat.     

Mitochondrial respiration in heart, liver, and kidney of copper-deficient rats

Morphological observations in some tissues indicate that dietary copper deficiency results in structural damage to mitochondria. The purpose of this study was to determine whether mitochondrial function is impaired as well. Male, weanling Sprague-Dawley rats were fed diets deficient or sufficient in copper for 4 weeks. Mitochondria were isolated from heart, liver, kidney cortex, and kidney medulla. P/O ratio, state 3 and state 4 respiration rates (oxygen consumed in the presence and absence of ADP, respectively), and acceptor control index (ratio of state 3:state 4) were determined using succinate or pyruvate/malate as substrate. State 3 respiration rate in mitochondria from copper-deficient hearts and livers was lower than in mitochondria from copper-sufficient hearts. Copper deficiency reduced the state 4 respiration rate only in cardiac mitochondria. Neither respiration rate was affected by copper deficiency in mitochondria from kidney medulla or cortex. P/O ratio was not significantly affected by copper deficiency in any tissue examined. Acceptor control index was reduced only in liver mitochondria. The observed decreases in respiration rates are consistent with decreased cytochrome c oxidase activity, shown by others to occur in mitochondria isolated from hearts and livers of copper-deficient rats.     

Increased respiration in skeletal muscle mitochondria from cold-acclimated ducklings: uncoupling effects of free fatty acids

Intermyofibrillar mitochondria from skeletal muscle (m. gastrocnemius) and liver mitochondria were isolated from cold-acclimated (4 degrees C) or control (30 degrees C) 4-week old ducklings. The respiratory rate of isolated mitochondria, with Na-succinate as substrate, was followed polarographically at 25 degrees C in order to determine the basal respiratory rate, the rate of respiration in the presence of free fatty acids (FFA) (Na-palmitate), and the fully uncoupled rate, after addition of FCCP. The basal respiration (which in liver mitochondria was unaffected by acclimation to cold) was higher (+53%) in intermyofibrillar mitochondria from cold-acclimated ducklings than from controls, and the maximal FCCP-stimulated respiration was also increased (+98%) by acclimation to cold. FFA-stimulated respiration increased as a function of FFA concentration in both types of mitochondria. The increase in respiration due to FFA was about double in intermyofibrillar mitochondria from cold-acclimated ducklings than that of controls, but in liver mitochondria there was no increase due to cold. The membrane potential was estimated by the dye safranine in the absence or in the presence of FFA in the incubation medium. There were no significant differences in the basal membrane potential in the two groups and the addition of FFA led to the same depolarization in both groups. The significance of these alterations for acclimation to cold is discussed.     

Adenine nucleotide translocation in liver mitochondria of hypothyroid rats.

In measurements using a disc filtration method, liver mitochondria obtained from hypothyroid rats translocate external ADP at 0 °C via the atractyloside-sensitive carrier much more slowly than do mitochondria from normal rats, confirming the findings of Portnay et al. (Biochem. Biophys. Res. Commun. 55, 17, 1973). The hypothyroid mitochondria contain 60% more ATP + ADP than do mitochondria from normals, but the excess nucleotides are not exchangeable and so do not contribute to translocation. A decrease in the first-order rate constant accounts for the decreased velocity. Neither a decrease in the number of translocator sites nor changes in ADP phosphorylation or ATPase activity seem to account for the abnormal kinetics of translocation. Although the filtration method limits the maximal translocation rate observed in normal mitochondria at temperatures above 17 °C that induce a fluid membrane state, no such transition is seen in mitochondria from hypothyroid rats up to 35 °C, indicating that the translocator is in an altered environment in hypothyroidism. Injecting a hypothyroid rat once with l-thyroxine corrects the abnormal compartmentation and produces a temperature-rate relationship like that in normal mitochondria in 3 days, a period which would accommodate the hormone actions reported on translation, membrane phospholipid synthesis, or fatty acid desaturation.     

Increased lipoprotein lipase activity of skeletal muscle in cold-acclimated rats

The activity of lipoprotein lipase (LPL) in the heart, diaphragm, and soleus muscles was markedly increased in cold-acclimated rats and it was even greater in rats treated with oxytetracycline (OTC) while exposed to cold. Other skeletal muscles studied had low and variable activities which were not significantly increased by cold acclimation or by cold plus OTC treatment. It appears therefore that, apart from the heart and the muscles involved in respiratory movements, LPL activity is primarily associated with those muscles which contain a predominance of slow-twitch oxidative fibers, and that the enzyme in muscle, heart, and diaphragm responds to cold acclimation and cold plus OTC treatment in a parallel fashion in these tissues.     

Mitochondrial alterations and apoptosis in smooth muscle from aged rats

We studied changes in mitochondrial morphology and function in the smooth muscle of rat colon. Under confocal microscopy, tissues loaded with potentiometric dye displayed rapid and spontaneous depolarization. Cyclosporin A (CsA), inhibitor of the permeability transition pore (PTP), caused an increase in mitochondrial membrane potential (ΔΨ_m) in tissues from adult young animals. In aged rats these changes were not observed. This suggests that physiological activation of PTP in aged rats is reduced. Electron microscopy showed alterations of the mitochondrial ultrastructure in tissues from aged rats involving a decreased definition of the cristae and fragmentation of the mitochondrial membranes. We also detected an increase in apoptotic cells in the smooth muscle from aged animals. Our results show that the aging process changes PTP activity, the ability to maintain ΔΨ_m and mitochondrial morphology. It is suggested that these can be associated with mitochondrial damage and cell death.     

Mitochondrial alterations and apoptosis in smooth muscle from aged rats

We studied changes in mitochondrial morphology and function in the smooth muscle of rat colon. Under confocal microscopy, tissues loaded with potentiometric dye displayed rapid and spontaneous depolarization. Cyclosporin A (CsA), inhibitor of the permeability transition pore (PTP), caused an increase in mitochondrial membrane potential (DeltaPsim) in tissues from adult young animals. In aged rats these changes were not observed. This suggests that physiological activation of PTP in aged rats is reduced. Electron microscopy showed alterations of the mitochondrial ultrastructure in tissues from aged rats involving a decreased definition of the cristae and fragmentation of the mitochondrial membranes. We also detected an increase in apoptotic cells in the smooth muscle from aged animals. Our results show that the aging process changes PTP activity, the ability to maintain DeltaPsim and mitochondrial morphology. It is suggested that these can be associated with mitochondrial damage and cell death.     

Loose-coupled subsarcolemmal mitochondria from muscle Rhomboideus in cold-acclimated piglets

1. Intermyofibrillar (IM) and subsarcolemmal (SM) mitochondria were isolated from rhomboideus (RH) and longissimus dorsi (LD) muscles of cold-acclimated (12 degrees C for 3 weeks) and control (23 degrees C) 8-week-old piglets. 2. Together with measurements of yield of mitochondrial protein and enzyme activities (cytochrome oxydase-CO; creatine kinase--CK), the respiratory rate of isolated mitochondria was followed polarographically in order to determine the respiratory control ratio (RCR) and consequently the tightness of coupling in response to ADP. 3. In control and cold-acclimated piglets, there were more IM than SM (P less than 0.05) and more mitochondria in RH than LD muscle (P less than 0.05). In both muscles, the yield of mitochondria was slightly but not significantly higher after cold acclimation than in controls. 4. In both muscles, IM were tightly coupled and their RCR (congruent to 4.5) were similar in both groups of piglets. RCR values were increased in the presence of bovine serum albumin (BSA). 5. In controls, SM exhibited lower respiration rates than IM (P less than 0.05) and were slightly coupled (RCR congruent to 2). Cold acclimation increases the loose-coupling of SM (P less than 0.05), especially in RH muscle. No changes appeared in the mitochondrial coupling after the addition of BSA. 6. After cold acclimation, CO and CK activities were increased in IM (P less than 0.05) while only CO activity was increased in SM (P less than 0.05). These results support a coupling defect in SM and therefore confirm mitochondrial respiration results.     

Ketone bodies in cold-acclimated rats

Acclimation temperature (28 or 5 degrees C) modifies acetoacetate (AA) and beta-hydroxybutyrate (BOH) levels in blood and liver. In the fed state AA and BOH levels were increased in blood and liver of 5 degrees C adapted rats. In the fasting state (24 or 48 hr) an antiketotic action of cold acclimation was observed. It was found to be more pronounced with high fat diet. These effects were more marked in the blood than in the liver. The variations in ketonemia are discussed with relation to the role of liver in cold adapted rats.