Early Lipid Raft-Related Changes: Interplay between Unilateral Denervation and Hindlimb Suspension

Muscle disuse and denervation leads to muscle atrophy, but underlying mechanisms can be different. Previously, we have found ceramide (Cer) accumulation and lipid raft disruption after acute hindlimb suspension (HS), a model of muscle disuse. Herein, using biochemical and fluorescent approaches the influence of unilateral denervation itself and in combination with short-term HS on membrane-related parameters of rat soleus muscle was studied. Denervation increased immunoexpression of sphingomyelinase and Cer in plasmalemmal regions, but decreased Cer content in the raft fraction and enhanced lipid raft integrity. Preliminary denervation suppressed (1) HS-induced Cer accumulation in plasmalemmal regions, shown for both nonraft and raft-fractions; (2) HS-mediated decrease in lipid raft integrity. Similar to denervation, inhibition of the sciatic nerve afferents with capsaicin itself increased Cer plasmalemmal immunoexpression, but attenuated the membrane-related effects of HS. Finally, both denervation and capsaicin treatment increased immunoexpression of proapoptotic protein Bax and inhibited HS-driven increase in antiapoptotic protein Bcl-2. Thus, denervation can increase lipid raft formation and attenuate HS-induced alterations probably due to decrease of Cer levels in the raft fraction. The effects of denervation could be at least partially caused by the loss of afferentation. The study points to the importance of motor and afferent inputs in control of Cer distribution and thereby stability of lipid rafts in the junctional and extrajunctional membranes of the muscle.

Clomipramine counteracts lipid raft disturbance due to short-term muscle disuse

Disuse-induced skeletal muscle dysfunction is a serious consequence of long-term spaceflight, numerous diseases and conditions for which treatment possibilities are still strictly limited. We have previously shown that acute hindlimb suspension (HS)-mediated disuse disrupts membrane lipid rafts in the unloaded muscle. Here, we investigated whether pretreatment of rats with the inhibitor of acid sphingomyelinase, clomipramine (1.25mg/g/day, intramuscularly, for 5days before HS), is able to hinder the loss in lipid raft integrity in response to 12h of HS. Clomipramine pretreatment significantly counteracted the decrease in labeling of the plasma membranes with lipid raft markers (fluorescent cholera toxin B subunit and bodipy-GM1-ganglioside) specifically in the junctional regions of the suspended soleus muscle. This was associated with: a) enhancing raft disrupting potential of exogenous sphingomyelinase in the junctional membranes; b) prevention of both ceramide accumulation and cholesterol loss; c) prevention of decline in nicotinic acetylcholine receptor labeling in the unloaded muscle. Our data suggest that sphingomyelinase-mediated raft disturbance serves as one of the earlier events in HS effects.

Water balance of lung and nitrogen oxide in blood at experimental autoimmune encephalomyelitis after capsaicin blockade of vagus nerve

THE PURPOSE OF THE RESEARCH

To study the water balance of lung and NO level in blood in experimental autoimmune encephalomyelitis combined with capsaicin blockade of vagus nerve.

METHODS

Experiments were conducted on 47 adult (16-week-old) male rats weighing 220-280 g. To simulate the experimental autoimmune encephalomyelitis (EAE) rats were subcutaneously injected with encephalitogenic mixture in complete Freund's adjuvant (0.2 ml; the content of inactivated Mycobacterium tuberculosis was 5 mg/ml) at the rate of 100 mg of homologous spinal cord homogenate per animal. Сapsaicin blockade was performed by bilateral application of 50 uM capsaicin («Sigma») on the neck portions of vagus nerves. The animals were divided into 4 groups: intact rats - control group1; rats with EAE; rats with capsaicin application on vagus nerve + EAE; sham operated rats subjected to vagus nerves allocation without the subsequent capsaicin application + EAE - control group 2. The next parameters were detected: the content of nitric oxide in blood plasma; protein content in broncho-alveolar lavage fluid; lung water balance indices including the amount of total, extra- and intravascular fluid and blood supply of lungs, which were calculated based on wet and dry lung mass and the hemoglobin content in blood and lung tissue determined by hemiglobincyanide method.

RESULTS

It was found that EAE is accompanied by an increase of total fluid, extravascular fluid (EVF) and blood supply of lungs on the background of increasing content of nitric oxide in arterial (art) and venous (ven) blood. In EAE and its combination with bilateral capsaicin blockade of vagus nerve a strong negative correlation between the NOart / NOven coefficient and EVF amount was found out. The blockade of capsaicin-sensitive vagal afferents normalized lung water balance impaired in EAE and restored the levels of nitric oxide in blood plasma.

CONCLUSION

The obtained results suggest that capsaicin-sensitive vagal afferents with NO-ergic mechanisms involvment take part in the development of pulmonary hyperhydration during experimental autoimmune encephalomyelitis.

[BINDING OF CELL-DERIVED MICROPARTICLES WITH FIBRIN IN BLOOD CLOTTING]

Direct effects of circulating blood microparticles on fibrin formation and structure were studied. Clots made from platelet-free plasma and from microparticle-depleted plasma obtained by filtration was studied in parallel, including clots from the microparticle-depleted plasma replenished with phospholipids. Fibrin formation was induced by exogenous thrombin without Ca2+ to prevent formation of endogenous thrombin and exclude indirect kinetic effects of microparticles related to thrombin generation. In the presence of natural microparticles or exogenous phospholipids the maximal turbidity of fibrin clots was significantly smaller, indicating structural distinctions from the clots formed in the absence of microparticles. Scanning electron microscopy and confocal microscopy showed that clots formed from platelet-free plasma, i. e. in the presence of microparticles, unlike clots from the microparticle-depleted plasma, contained 0.1-0.5-μm-large CD61-positive granules associated with fibrin fibers that were identical to the particles found on the surface of filters used for microparticle removal. The results show that platelet-derived microparticles bind to fibrin and affect its structure. The revealed interactions of cell-derived microparticles with fibrin highlight a previously unknown role of microparticles in hemostasis and thrombosis as constituents and modulators of a fibrin clot structure.

[METABOLIC ACTIVITY OF LUNG AT EXPERIMENTAL BRAIN ISCHEMIA IN CONDITION OF CAPSAICIN BLOCKADE OF VAGUS NERVE]

In rats with ligation of both common carotid arteries in condition of bilateral capsaicin blockade of vagus nerve the metabolic functions of the lungs associated with their participation in the regulation of hemostasis, lipid composition of blood plasma and lung surfactant were investigated. It is shown that cerebral ischemia is accompanied by changes in the fractional composition of phospholipids in both arterial and venous blood, as well as in pulmonary surfactant, and the decrease of the lung hypocoagulation effect. The phagocytic activity of alveolar macrophages (as one of the factors involved in surfactant lipids metabolism) in brain ischemia is reduced. After the blockade of capsaicin-sensitive vagal afferents the changes in surfactant and plasma phospholipids caused by cerebral ischemia, are abolished, hypocoagulation effect of lung restores, but the functional activity of macrophages remains decreased. These findings suggest that capsaicin-sensitive vagal afferents are involved in the development of disregulatory disorders of lung metabolic function in cerebral ischemia.

[EFFECTS OF LIGHT OR DARK DEPRIVATION ON PERFORMANCE AND LACTATE LEVELS IN RAT BLOOD]

The dynamics of rat's swimming test with a load after 10 daily deprivation of light or dark were investigated. It was established that in the control group in nature illumination daily physical swimming with a load to full exhaustion from the first to the third day of the experiment, there was an increase of active swimming time indicator followed by stabilization. In groups of animals kept before bringing swimming test in a day and night lighting or darkening around the clock, there was an increase in swimming time only on the first day of the experiment, and the next days there was a decrease of efficiency. After a five-day cycle of the swimming load the level of lactate in the blood of control animals was increased, and experienced - has not changed in comparison with the intact, not subjected to any stress.

INTRAOCULAR PRESSURE AND EYE HYDRODYNAMICS DURING BRIEF HEAD-DOWN TILT

Intraocular pressure (IOP) and eye hydrodynamics (aqueous outflow easiness rate (C) and moisture chamber production (F)) were studied in 9 adult volunteers subjected to the hypogravity effects of head-down tilt (HDT) at -15⁰ to the horizontal plane. The volunteers stayed in the horizontal and tilted positions for 10 minutes. IOP was measured according to Maklakov (tonometer 5 g), C and F - according to Nesterov (simplified tonography). In parallel, heart rate (HR) and systolic and diastolic blood pressures (SBP and DBP) were measured in the sitting, lying and tilted positions. In HDT IOP rose 10.3 % (p < 0.05) and C reduced 60 % (p < 0.05); F showed an uncertain trend down by 59 % (p > 0.05). Increase of the Bekker coefficient by 168 % (p < 0.05) could testify interconnection of the increased IOP and impaired moisture outflow. Moreover, in HDT DBP showed a rise while HR decreased. These results suggest that during brief tilt- down IOP increases not only because of a greater filling of the choroid vessels, but also because of retarded outflow of the intraocular fluid. The downward trend in fluid production can be a compensatory reaction to increased'IOP.

[Surfactant and water balance of lung in intracerebral hemorrhage at conditions of capsaicin blockade of vagus nerve]

It is known that intracranial hemorrhage (ICH) is accompanied by the development of neurogenic pulmonary edema and insufficiency of surfactant function. The present study was undertaken for evaluation of the role of vagal afferents in the mechanisms of ICH effects on pulmonary surfactant and water balance of the lung. We explored the surface activity and biochemical composition of surfactant, as well as blood supply, total, intravascular and extravascular fluid content in lung after ICH, simulated by intraventricular administration of autologous blood against the background of bilateral blockade of capsaicin-sensitive vagal affere its. The blockade was caused by the capsaicin application (50 mcmol) on the cervical part of the nerves. Intracerebralhemorrhage was accompanied by the decrease of surfactant activity which appeared by the enhancement of minimal, maximal and static surface tension of bronchoalveolar lavage fluid (BAL), the reduction of total phospholipids including their main fraction phosphatidylcholine, the increase of lysophosphatidyicholine content and hyperhydration of the lung. The level of total proteins in BAL elevated, confirmed the enhanced permeability of the alveolar-blood barrier. The exhaustion of neuropeptides in capsaicin-sensitive vagal afferents led to the partial restoration of surface active properties of lung, normalization of phospholipids and protein contents and water balance parameters. The obtained results suggest that capsaicin-sensitive vagal afferents play a pivotal role in the disturbances of surfactant function and water balance of the lung after ICH.

[Sphingolipids in skeletal muscles of C57B1/6 mice after short-term simulated microgravity]

For the first time in skeletal muscle, the sphingolipid profile and key enzymes involved in the generation of ceramide in cells were investigated in simulated microgravity. It was found that, in C57B1/6 mice, the 4-day hindlimb unloading, in addition to reducing the mass of m. soleus, leads to the ceramide accumulation (3-fold) and the decrease of sphingomyelin content in this muscle (7.2-fold), as well as to the increase (2.7-fold) of protein level of acid sphingomyelinase. In a loaded m. biceps brachii the amount of ceramide is also enhanced, but both the amount of sphingomyelin and sphingomyelinase, as well as the muscle mass do not change, while the level of serine palmitoyltranspherase becomes significantly lower than in control mice. Taking into account the negative effects of ceramide in skeletal muscle (insulin resistance, inhibition of protein synthesis and increase of its decay) we can assume that sphingolipid mechanisms may be involved in the development of structural and functional abnormalities of skeletal muscle under conditions of weightlessness.

[Surfactant system of lung in rats with different resistance to stress under alloxan diabetes]

It is shown that the surface active properties of lung under experimental diabetes mellitus was decreased on the background of increased LPL content in alveolar space. Surfactant changes correlated with the level of glucose, glycosylated hemoglobin and 11-oxycorticosteroids in blood. The obtained results indicate that the degree of impairment in the pulmonary surfactant system in alloxan diabetes depends on the resistance or susceptibility of animals to stress.

Effect of long-term simulated weightlessness on surfactant and water balance in mouse lungs

Weightlessness produces adaptive and maladaptive changes in the respiratory system. We assessed the effects of 30-day antiorthostatic hanging as a model of microgravity on the water balance in the lungs and surface activity and phospholipid composition of pulmonary surfactant in C57Bl/6 mice. Long-term antiorthostatic hanging increased water content in the lungs and reduced surface-active properties of the surfactant. This was accompanied by an increase in the content of alveolar phospholipids and changes in their fractional composition (increase in the relative content of lysophosphatidylcholine and phosphatidylethanolamine).

[Stress-resistance and the condition of surfactant system and water balance in the lung of suspended rats]

White male rats with the body mass of 180-220 grams were distributed into the open-field active (presumably stress-resistant) and open-field inactive (presumably stress vulnerable) groups for a 10-day experimental suspension with the purpose to evaluate the surfactant activity in bronchoalveolar lavages, total phospholipids and their fractions, and water balance in the lung. In modeled microgravity, augmented blood filling of the rat's lung increases the alveolar phospholipid content and alters the phospholipid fractional composition in the pulmonary surfactant. Ten-day suspension raises pulmonary surfactant activity to a greater extent in stress-resistant animals rather than in their stress vulnerable peers.

[The role of individual stress resistance in realization of immobilization and zoosocial stress effects on pulmonary surfactant system]

The aim of the present study was to investigate the effect of chronic exposure to immobilization and psychosocial stress on surface activity, biochemical composition of pulmonary surfactant and lung fluid balance of rats with different stress-resistance. It is shown that both types of stress lead to elevation of lysophospholipids level and decrease of surface-active properties of pulmonary surfactant, more prominent in stress-vulnerable rats. Blood supply was decreased and extravascular fluid was increased under the psychosocial stress only in stress-vulnerable animals, in all rest cases the blood supply was increased and the content of extravascular fluid was not changed. Surfactant alteration was coupled on the level of 11-OCS in the blood and amount of fluid in the lungs. The obtained results indicate that different degree of impairment in the pulmonary surfactant system during immobilization and psychosocial conflicts depends on different resistance to emotional stress.

[Lipid composition in erythrocytic membranes of rats with various stress resistance during repeated immobilization]

The dependence between variation of erythrocyte phospholipid composition and stress resistance was studied in chronic experiment on nonline male albino rats, previously differed by their behavior in the 'open field' test. A significant exhausting of membrane pool by the basic classes of phospholipids was registered under influence of 2 hours daily immobilization during 5, 10, 20, 30 days, however, their metabolism for resistant and predisposed to stress animals flows variously.

[Influence of stress-resistance on changes in the rat prefrontal cortex phospholipid composition during chronic immobilization]

The dependence between variation of prefrontal cortex phospholipid composition and stress-resistance was studied in chronic experiment on nonline male albino rats, previously differed by their behavior in the "open field" test. A significant lack of basic classes of phospholipids was registered in prefrontal cortex under the effect of a 2-hour daily immobilization during 5, 10, 15, 30 days. We proposed criteria of individual stress-resistance. These criteria could be interesting for improvement of stability under extreme conditions with the aid of correction of neuronal biogenesis.

[The effect of prolonged repeated immobilisation on metabolism of biogenic amins in the lungs of rats with different prognostic resistance against emotional stress]

In chronic experiment on male albino rats divided into active and passive groups according to their behavior in "open field" test significant differences in character of lung metabolic activity upon biogenic amines were found out. In both groups the highest level of histamine in arterial and venous blood was registered on the 5th day, 5-hydroxytriptamine--on the 10-20 days and catecholamine--on the 20th day of the experiment. On the 5th day lungs pf passive rats uptaked catecholamines from blood whereas lungs of active ones put in into blood. Histamine and 5-hydroxytriptamine uptake took place on the 5th day only in active rats, but on the 10th only lungs of passive ones absorbed 5-hydroxytriptamine from blood. Intergroup differences of lung metabolic activity upon histamine and 5-hydroxytriptamine were removed on the 20th day. Lung monoamine oxydase activity was significantly increased in active rats and decreased in passive ones in all periods of experiment.

[Properties of lung surfactant during changes in capsaicin-sensitive vagal afferents under conditions of emotional stress]

In this work, we investigated surface active properties and biochemical composition of pulmonary surfactant under emotional stress in condition of neuropeptides pool exhaustion in capsaicin-sensitive afferents of the vagus nerve. It is shown that stress is accompanied by decrease of lung surface active properties and increase of total phospholipids content as result of phosphatidylcholine and lysophospholipid fraction rise. After capsaicin application on the cervical part of the right vagus nerve stress-induced alterations in ipsilateral lung become less considerable, whereas all spectra of changes in contralateral lung is remained.

Effect of locus coeruleus stimulation on ocular hypertension and pathology of pulmonary surfactant during chronic emotional stress

In chronic experiments on rabbits and rats, parameters of eye homeostasis (intraocular pressure and ocular hydrodynamics) and lungs (water balance and surface-active properties of surfactant) were studied during electrical stimulation of the locus coeruleus against the background of chronic stress induced in rabbits by repeated electrical stimulation of the ventromedial nucleus and in rats by daily immobilization on a platform. Stimulation of the locus coeruleus eliminated ocular hypertension of hypothalamic origin and stress-induced disturbances in surface activity, blood volume, and water balance in the lungs.

[Substance P as a factor enhancing resistance of the surfactant lung system to chronic immobilization stress]

In chronic experiments on non-line white rats the influence of system (intraperitoneal) and central (into the lateral brain ventricle) administration of substance P on lung surfactant system was studied in stressed and non-stressed animals. A single injection of substance P limited pulmonary surfactant activity disorders in immobilisation stress. Stress-induced increase of phospholipids level in broncho-alveolar lavage fluid remained the same in intracerebroventricular administration and was partly reduced in intraperitoneal one. In intact rats, a single injection of peptide was accompanied by alveolar phospholipids accumulation. In rabbits, multiple intracerebroventricular injections of substance P enhanced the opposite effect.