Effects of hibernation on mitochondrial regulation and metabolic capacities in myocardium of painted turtle (Chrysemys picta)

Painted turtles hibernating during winter may endure long-term exposure to low temperature and anoxia. These two conditions may affect the aerobic capacity of a tissue and might be of particular importance to the cardiac muscle normally highly reliant on aerobic energy production. The present study addressed how hibernation affects respiratory characteristics of mitochondria in situ and the metabolic pattern of turtle myocardium. Painted turtles were acclimated to control (25 degrees C), cold (5 degrees C) normoxic and cold anoxic conditions. In saponin-skinned myocardial fibres, cold acclimation increased mitochondrial respiratory capacity and decreased apparent ADP-affinity. Concomitant anoxia did not affect this. Creatine increased the apparent ADP-affinity to similar values in the three acclimation groups, suggesting a functional coupling of creatine kinase to mitochondrial respiration. As to the metabolic pattern, cold acclimation decreased glycolytic capacity in terms of pyruvate kinase activity and increased lactate dehydrogenase (LHD) activity. Concomitant anoxia counteracted the cold-induced decrease in pyruvate kinase activity and increased creatine kinase activity. In conclusion, cold acclimation seems to increase aerobic and decrease anaerobic energy production capacity in painted turtle myocardium. Importantly, anoxia does not affect the mitochondrial functional integrity but seems to increase the capacity for anaerobic energy production and energy buffering.     

Cardiac remodeling in fish: strategies to maintain heart function during temperature Change

Rainbow trout remain active in waters that seasonally change between 4°C and 20°C. To explore how these fish are able to maintain cardiac function over this temperature range we characterized changes in cardiac morphology, contractile function, and the expression of contractile proteins in trout following acclimation to 4°C (cold), 12°C (control), and 17°C (warm). The relative ventricular mass (RVM) of the cold acclimated male fish was significantly greater than that of males in the control group. In addition, the compact myocardium of the cold acclimated male hearts was thinner compared to controls while the amount of spongy myocardium was found to have increased. Cold acclimation also caused an increase in connective tissue content, as well as muscle bundle area in the spongy myocardium of the male fish. Conversely, warm acclimation of male fish caused an increase in the thickness of the compact myocardium and a decrease in the amount of spongy myocardium. There was also a decrease in connective tissue content in both myocardial layers. In contrast, there was no change in the RVM or connective tissue content in the hearts of female trout with warm or cold acclimation. Cold acclimation also caused a 50% increase in the maximal rate of cardiac AM Mg(2+)-ATPase but did not influence the Ca(2+) sensitivity of this enzyme. To identify a mechanism for this change we utilized two-dimensional difference gel electrophoresis to characterize changes in the cardiac contractile proteins. Cold acclimation caused subtle changes in the phosphorylation state of the slow skeletal isoform of troponin T found in the heart, as well as of myosin binding protein C. These results demonstrate that acclimation of trout to warm and cold temperatures has opposing effects on cardiac morphology and tissue composition and that this results in distinct warm and cold cardiac phenotypes.     

The activity of receptor guanylyl cyclases in tissues of rats with neonatal streptozotocin diabetus mellitus and the influence of intranasal administration of insulin and serotonin

Functional activity of hormanal signaling systems and their sensitivity to regulatory actions of hormones in diabetes mellitus (DM) and its complications are altered. The activity of receptor forms of guanylyl cyclases (rGC) sensitive to natriuretic peptides, ANP and CNP, in tissues of female rats with 240-days neonatal streptozotocin DM and the influence of intranasal administration of insulin and serotonin (6 weeks, daily dose is 0.48 IU of insulin or 20 microg of serotonin to rat) on this activity were studied. In diabetic animals, the increase of the basal activity of rGC in the myocardium and its decrease in the uterus and ovaries were found, whereas the brain showed no differences from control animals. The treatment of diabetic rats with insulin led to a decrease in the basal activity of rGC in the myocardium and to its restoration to normal level in the ovaries. Serotonin treatment induced a less pronounced compared with insulin decrease in the basal activity of the enzyme in the myocardium and also a slight increase the activity in the brain. In the myocardium of diabetic rats, the weakening of GC stimulating effect of ANP and, on the contrary, the strengthening of CNP effect were observed. In the ovaries, GC stimulating effect of CNP and, to a lesser degree, the corresponding effect of ANP were decreased. In the uterus and the brain, the sensitivity of rGC to hormones was practically not changed. The administration of insulin to diabetic rats induced an increase in GC effect of ANP in the myocardium to its values in control animals and a decrease in CNP effect as well as in partially restored GC effect of CNP in the ovaries. Serotonin treatment led to some increase in the effects of natriuretic peptides in the brain of both control and diabetic animals. Summing up, in neonatal model of type 2 DM in the myocardium and the tissues of reproductive system of rats the functioning of natriuretic peptide-sensitive rGC is altered in the myocardium and the tissues of reproductive system of model rats with neonatal type 2 DM. Treatment of animals with insulin substantially restores rGC activity while intranasal administration of serotonin has little effect.     

Evaluation of the temperature effect on contractility of frog myocardium]

Dynamics of the parameters of mechanical activity of the frog isolated myocardium was studied under conditions of temperature variations. Within the temperature range of 0-35 degrees C the temperature decrease leads to a rise in the strength of contractions. Meanwhile the velocity of contractions reaches its optimum value at 20 degrees C. The velocity of contractions proved to be a more adequate and sensitive criterion for evaluating the cold effect on contractility than the strength of contractions. From the analysis of the evidence obtained it is concluded that muscle contractility of the heart is depressed on cooling.     

Quick adaptation of the myocardium and autonomic nervous regulation of the cardiac rhythm in 10- to 11-year-old children operating a computer

A study of quick adaptation of the myocardium of subjects operating a computer, depending on the adaptive capacities of the body, was conducted in 100 children with ages varying between 10 and 11 years using the electrocardiography method for the analysis of heart rate variability. Significant differences in the bioelectrical processes in the myocardium and autonomic nervous regulation of the cardiac rhythm (CR) were found in children with different adaptive capacities of the body. Quick adaptation to the operator activity in children with a good adaptive capacity is characterized by intensification of atrial activity and metabolic processes in the myocardium, as well as by a shortened duration of the cardiac cycle due to a shorter diastolic time, determined by increased sympathetic influences on the CR. In children with a decreased adaptive capacity, a decrease in the atrial excitability and myocardial metabolism, an increase in the systolic time, a decrease in the diastolic time, and an increase in parasympathetic influences on the CR are observed.     

Seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel (Citellus citellus): the effect of cold.

1. The activity of antioxidant defense enzymes (SOD, CAT, GSH-Px and GST) was analysed during the autumn and winter in the ground squirrel adapted to 30 degrees C and subsequently exposed to cold for 6 and 24 hr. 2. The liver CAT activity as well as the IBAT CAT and GSH-Px activities differed between animals adapted to 30 degrees C, studied in autumn, and those studied in winter. 3. MnSOD activity in the liver was increased in autumn but decreased in winter after 6 hr cold exposure reaching the control level 24 hr later. Cold exposure induced a decrease in CAT activity (except after 24 hr cold exposure in winter) and an increase in GSH-Px activity. Lower GST activity was found after 24 hr exposure to cold in winter. 4. The IBAT SOD activity decreased under the influence of cold during both seasons with a tendency to return to the control level only in winter. Cold exposure produced a decrease in GST in both seasons and CAT activity in autumn. GSH-Px activity was increased in winter only. 5. The results indicate a seasonal dependence of the activity of antioxidant defence enzymes in the ground squirrel. Seasonal influence was evidenced in animals exposed to cold as well.     

Histostereologic analysis of the myocardium of homoiothermic animals during cooling

A stereologic study of the myocardium exposure to cold for 4 hours, 8 and 16 days was carried out on Wistar rats. It has been shown that during the first 8 days acute hemodynamic disorders and cardiomyocyte contractures developed. These changes were followed by a decrease in the volume and surface capillary density resulting in the impairment of transcapillary exchange and reduction of the intracellular regeneration processes in cardiomyocytes. By the 16th day the compensatory-adaptive reactions developed, i.e., the volume and surface density of endothelial cells and capillaries was increased. At the same time the lysis processes caused by the general decrease in the inflow of plastic substances to the myocardium due to the increase in thermogenesis were revealed in part of cardiomyocytes. These changes in parenchymatous cells were accompanied by the intensification of desmoplastic reactions in the myocardial stroma.     

Activity of receptor guanylyl cyclases in rats with neonatal streptozotocin diabetes and effect of intranasal administration of insulin and serotonin

In diabetes mellitus (DM) and its complications the functional activity of hormonal signaling systems and their sensitivity to the regulatory action of hormones are changed. We studied the activity of receptor forms of guanylyl cyclase (rGC) sensitive to natriuretic peptides ANP and CNP in the tissues of female rats with 240 day neonatal streptozotocin DM and the effects of intranasal administration of insulin and serotonin (6 weeks, daily dose for rat is 0.48 IU insulin or 20 μg serotonin). In diabetic rats, the increase of the basal rGC activity in the myocardium and its decrease in the uterus and ovaries were found, while in the brain, there were no differences from the control. The treatment of diabetic rats with insulin led to a decrease of the basal rGC activity in the myocardium and its restoration to a normal level in the ovaries. The administration of serotonin produced a less pronounced decrease in the basal enzyme activity in the myocardium compared to insulin and an insignificant increase in the brain. In the myocardium of diabetic rats, the guanylyl cyclase (GC)-stimulating effect of ANP was attenuated, whereas the CNP effect was enhanced; in the ovaries, the GC-stimulating effect of CNP and, to a lesser degree, the effect of ANP were decreased. In the uterus and brain of a diabetic rats, the rGC sensitivity to hormones was practically did not change. The administration of insulin to diabetic rats induces an increase of GC effect of ANP in the myocardium to its values in control and a decrease of CNP effect, as well as partially restored GC effect of CNP in the ovaries under the influence of CNP. The administration of serotonin somewhat enhanced effect of natriuretic peptides in the brain of both control and diabetic animals. Thus, in the neonatal model of type-2 DM in the myocardium and the tissues of the reproductive systems of rats, the functioning of natriuretic peptide-sensitive rGC is changed. The treatment of animals by insulin substantially restores rGC activity, while the intranasal serotonin administration has a little effect.     

Bioelectrical cardiac processes during induced systemic vasodilation in men under conditions of the Russian North

Features of the electrocardiogram (ECG) at physiological rest and upon a single administration of nitroglycerin (NG) were studied in healthy young male residents of the Russian North in summer and in winter. The activity of the sinoatrial node and excitation of the heart ventricles were shown to increase in winter. Irrespective of the season, amplitude components of the ECG were the predominant factors in the organization of the cardiac activity and temporal components were second in importance. NG was shown to induce unequal ECG changes in the seasons with contrasting temperatures: in winter, more components were involved in the response, with a characteristic deceleration of atrioventricular conduction of excitation in the heart, as well as the formation of a determined factor structure of the processes of depolarization and early repolarization of the myocardium. In the cold season, the individual features of the cardiac activity retained their general features in most cases (89.2%) regardless of the physiological status of the heart. Among individuals with high depolarization of the myocardium and low depolarization of its basal segments, reversion to another type of the functional state was observed in 10.8% of cases. It was supposed that, even in a relatively healthy man, the chronic influence of cold on the body in the North markedly changes the cardiac activity, increasing the functional reactivity of the mechanisms of myogenic autoregulation to a decreased venous return.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 49–58.Original Russian Text Copyright © 2005 by Bocharov, Dernovoi.     

Cardiac Effects of the Class III Antiarrhythmic Drugs Amiodarone and Nibentan

The effects of Amiodarone and Nibentan on the postextrasystolic and postrest reactions were studied with normal rat myocardium and (for Amiodarone only) with myocardial strips isolated from patients with coronary heart disease (CHD). One-third of the patient samples displayed spontaneous activity that could be effectively suppressed by Amiodarone. All other samples displayed postrest inotropic effects of two types, with 30 or 70% decreases in the parameters of the contraction-relaxation cycle. Amiodarone did not influence the reaction of the first type but increased the postrest inotropic response of the second type. Both Amiodarone and Nibentan decreased the postextrasystolic inotropic response of the normal rat myocardium and simultaneously increased the postextrasystolic contraction. In addition, these drugs nearly doubled postrest potentiation. In the patient myocardium samples, however, Amiodarone did not decrease the amplitude of the extrasystolic contraction but increased postextrasystolic potentiation. It was supposed that, in the myocardium of some CHD patients (as well as in the rat myocardium), Amiodarone increases the ability of the sarcoplasmic reticulum to accumulate calcium ions. The same was supposed for the effects observed for Nibentan in tests with the rat myocardium. This phenomenon may contribute to the suppression of abnormal activity of the myocardium and strengthen the direct antiarrhythmic effect of Amiodarone.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 4, 2005, pp. 113–118.Original Russian Text Copyright © 2005 by Ugdyzhekova, Afanas’ev, Lukavskaya, Popov.     

Myocardial ER chaperone activation and protein degradation occurs due to synergistic,not individual,cold and hypoxic stress

Environmental stress at high altitude affects the myocardium at the physiological and molecular level. Characterized by hypobaric hypoxia and low temperatures, the cumulative impact of these stressors on the protein folding homeostasis in the heart is yet unexplored. The present study evaluates the collective effect of cold and hypoxia on the myocardial protein oxidation and activation of the endoplasmic reticulum (ER) stress response. Adult rats were exposed to either a singular acute stress of cold (10 °C; C), hypobaric hypoxia (7620 m; H) or simultaneously to both cold and hypobaric hypoxia (CH) for 6 h. Hypoxic stress amplified the free radical generation in H and CH groups, leading to enhanced HIF-1α expression. Coupled to cold stress, reduced oxygen availability caused substantial protein oxidative modifications, as well as cardiac tissue injury and matrix remodeling, evident in the histological staining. Presence of oxidized proteins caused a significant upregulation in expression of ER chaperones GRP78 and PDI in the cold hypoxia exposed animals. Enhanced proteolytic activity signaled the removal of misfolded proteins. Linked intricately to cellular stress response, cell survival kinases were expressed higher in CH group; however apoptotic CHOP (C/EBP homologous protein) expression remained unaltered. Administration of ER stress inducer, tunicamycin along with cold hypoxic stress, caused a discernible increase in protein oxidation and GRP78 expression, along with a significant elevation in proteasome and apoptotic activity. Highlighting the significance of a synergistic, rather than individual, effect of low oxygen and temperature on the protein folding machinery, our study provides evidence for the activation of ER stress response in the myocardium under acute high altitude stress.     

Effect of prostaglandin E2 on the development of adrenaline-induced myocardiodystrophy

In experiments on male rats it was established, that injection of prostaglandin E2 (PGE2) before the injection of adrenaline decrease essentially the activity of peroxidation of lipids in myocardium in comparison with animals which had only injection of adrenaline. Accordingly, pH is a factor, that limited a damage of myocardium on the development of adrenaline myocardiodystrophy.     

The enhancement of body resistance to combined exposure to immobilization and cold with thyroid hormones]

In experiments on 123 male rats have been found that the combination of immobilizing and cold (4 degrees C) stresses during 6 hours results in the formation of 4.5 gastric mucosa ulcers in every rat, marked activation of lipoperoxidation and depression of antioxidant activity of myocardium, significant increase of relative mass of adrenal glands, decrease of spleen mass and death of 80% animals accompanied by the reduction of concentration of thyroid hormones in blood serum and hypothermia (to 28 degrees C). The prestress injection of small doses of thyroidine decreased of mucosa defect rate and the number of ulcers to 2.8, made less marked the changes of relative mass of adrenal glands and spleen and the changes of concentration of thyroid hormones in blood serum, significantly limited the activation of lipoperoxidation, depression of power in antioxidant systems of myocardium, hypothermia (to 32.5 degrees C) and significantly increased the survival rate (to 70%).     

Effect of Adaptation to Graduated Physical Exercises on the Function of the Rat Myocardium

On isolated hearts obtained from control rats and rats subjected to regular physical exercises (forced swimming) during 6 weeks, we studied the contractile activity of the heart, resistance of the myocardium to ischemia/reperfusion-induced injuries, as well as the dependence of the developed and end-diastolic pressures in the aortic ventricle (AV) on the strain of the myocardium (by means of a dosed increase in the volume of a polyethylene reservoir inserted into the ventricle). It was demonstrated that adaptation to regular graduated physical exercises exerts a positive effect on the functional state of the AV myocardium and its contractile function. This was manifested in intensification of the contractile activity of the myocardium, a decrease in its oxygen “job cost,” and an increase in the resistance to injuries induced by ischemia-reperfusion. In addition, regular physical trainings led to an increase in the resistance of the AV myocardium to the strain. In trained rats, the plateau of the Frank–Starling plot was significantly greater than that in control animals, while the rigidity of the AV myocardium was significantly lower. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 41–47, January–February, 2009.     

Maintained contractile reserve in a transgenic mouse model of myocardial stunning

Cardiac excitation-contraction (E-C) coupling is impaired at the myofilament level in the reversible postischemic dysfunction known as "stunned" myocardium. We characterized tension development and calcium cycling in intact isolated trabeculae from transgenic (TG) mice expressing the major proteolytic degradation fragment of troponin I (TnI) found in stunned myocardium (TnI(1-193)) and determined the ATPase activity of myofibrils extracted from TG and non-TG mouse hearts. The phenotype of these mice at baseline recapitulates that of stunning. Here, we address the question of whether contractile reserve is preserved in these mice, as it is in genuine stunned myocardium. During twitch contractions, calcium cycling was normal, whereas tension was greatly reduced, compared with non-TG controls. A decrease in maximum Ca2+-activated tension and Ca2+ desensitization of the myofilaments accounted for this contractile dysfunction. The decrease in maximum tension was paralleled by an equivalent decrease in maximum Ca2+-activated myofibrillar ATPase activity. Exposure to high calcium or isoproterenol recruited a sizable contractile reserve in TG muscles, which was proportionately similar to that in control muscles but scaled downward in amplitude. These results suggest that calcium regulatory pathways and beta-adrenergic signal transduction remain intact in isolated trabeculae from stunned TG mice, further recapitulating key features of genuine stunned myocardium.     

Phosphorylase activity and glycogen content in cerebral and myocardium tissues in rats of different age

The phosphorylase activity (EC 2.4.1.1) and the glycogen content were determined in the brain and myocardium of adult and old rats. In the cortex and while substance of great cerebral hemispheres, the phosphorylase a activity decreases and the phosphorylase b activity increases, while the total enzyme activity remains unchanged with aging. In the myocardium, the activity of phosphorylase a increases, while that of phophorylase b decreases against a background of an insignificant decrease in the total phosphorylase activity. During aging, the glycogen content decreases sharply in the myocardium, whereas in the cerebral tissue it remains unchanged. Age peculiarities of the adrenaline effect upon myocardial phosphorylase activity are presented.     

Calcium-dependent proteolysis in the myocardium of rats subjected to stress

Activity of a calcium-dependent neutral protease (calpain II) and its specific endogenous inhibitor was investigated in the myocardium of rats subjected to different stressors: cold, anaesthesia, 24 and 48 h starvation and food restriction for 7 and 14 days. Enzyme and inhibitor activities were determined in the 37,200 g supernatant of homogenates prepared from the free left ventricular wall of the heart. The specific activity of the myocardial calcium-dependent proteinase increased in all rats exposed to stressful stimuli, reaching maximum values in animals starved for 48 hours. Decrease in the specific activity of the inhibitor accompanied the changes in enzyme activity. Differences from normal control values were statistically significant in the starved animals and in animals fed a restricted diet for 7 or 14 days. These observations suggest that interaction between calpain II and its specific inhibitor plays a role in the regulation of the enzyme activity and furthermore, that stressful stimuli lead to increased calcium-dependent proteolysis in the myocardium.     

The effect of hypothermia on the Ca2+-pump in sarcoplasmatic reticulum during autolysis of the myocardium

Certain hypothermia action mechanisms on Ca2(+)-pump of the sarcoplasmic reticulum in rat myocardium autolysis are investigated. The complex dependence of Ca2(+)-transporting system preservation in autolysis on the depth of hypothermia is shown. The role of lipid peroxidation and endoproteolysis in a decrease of the autolysing myocardium Ca2(+)-pump activity is considered. A conclusion is drawn that hypothermia does not affect the accumulation of peroxidation products in sarcoplasmic reticulum membranes during myocardium autolysis. The protective action of deep hypothermia on the autolysing myocardium Ca2(+)-pump is realized, at least partially, due to an increase in the Ca2(+)-ATPase active molecules number.     

Disturbance of transduction of adenylyl cyclase-inhibiting hormonal signaling in the myocardium and brain of rats with experimental type 2 diabetes

Presently, our work, as well as that of other authors, has produced convincing evidence in favor of the idea that disturbances in hormonal signaling systems are one of the main causes of the development of pathological alterations and complications in diabetes. However, the molecular mechanisms underlying these disturbances remain practically unstudied, particularly in insulin-independent type 2 diabetes. Using a neonatal streptozotocin model of type 2 diabetes, whose duration was either 80 or 180 days, we studied changes in the functional activity of components of the hormone-regulated adenylyl cyclase (AC) signaling system in the myocardium and brain striatum of diabetic rats as compared with control animals. In diabetes, the G_i-realized process of transduction of the hormonal signal inhibiting AC activity has been shown to be markedly impaired. This is manifested as a decrease of the inhibitory effect of hormones on AC activity and an attenuation of their stimulation of the G-protein’s GTP-binding activity. In the case of noradrenaline (myocardium), the inhibitory pathway of the AC system regulation is completely suppressed, while the stimulatory pathway is preserved. An increase in the duration of diabetes development from 80 to 180 days leads to some decrease in the transduction of hormonal signals realized via G_i-proteins. The stimulatory effects of biogenic amines and relaxin on AC activity and GTP binding in the myocardium and brain of diabetic rats change relatively little, both in the 80-and in the 180-day diabetes. Thus, in the experimental type 2 diabetes, disturbances in G_i-protein coupled signal cascades are primarily observed, through which hormones realize their inhibition of AC activity.     

Characteristics of responses of the sympatho-adrenal system to various types of cooling

Fast cooling involving the dynamic activity of the skin cold receptors seems to establish a condition for changes in catecholamine concentration at a lesser decrease of body temperature as compared with slow cooling.