Effect of intermittent high altitude hypoxia on the structure and enzymatic activity of cardiac myosin

The time course of structural and enzymatic changes in cardiac myosin was studied in the right and left ventricle of rats exposed to intermittent high altitude (IHA) hypoxia. In the controls, ATPase activity and myosin structure in both ventricles was the same. After the third exposure to simulated high altitude (2 600 m), myosin enzymatic activity rose significantly in the left ventricle and a significant right-left difference appeared. In the next phase of adaptation (11 exposures, 6 000 m), myosin ATPase activity fell in both ventricles and the right-left difference disappeared. After the 16th exposure (7 000 m), enzymatic activity increased again in both ventricles and attained control values. IHA also produced significant structural changes in cardiac myosin, particularly in the rigaht ventricle. The changes were characterized by the formation of myosin aggregates with significantly lower ATPase activity that the myosin monomer. The time course and localization of structural and enzymatic changes in cardiac myosin corresponded to the morphological damage to the heart fibres.     

Changes in the expression and/or activation of regulatory proteins in rat hearts adapted to chronic hypoxia

Chronic intermittent high altitude (IHA) hypoxia results in long-term adaptation protecting the heart against acute ischemia/reperfusion injury; however, molecular mechanisms of this phenomenon are not completely elucidated so far. The present study was aimed at investigation of a modulating effect of IHA hypoxia on the expression and/or activation of selected regulatory proteins, with particular emphasis on differential responses in the right ventricle (RV) and left ventricle (LV). Adult male Wistar rats were exposed to IHA hypoxia of 7000 m simulated in a hypobaric chamber (8 h/day, 25 exposures), and protein contents and activities in myocardial fractions were determined by Western blot analysis. In markedly hypertrophic RV of hypoxic rats, gelatinolytic activity of MMP-2 and protein levels of carbonic anhydrase IX (a marker of hypoxia) were significantly enhanced. Study of mitogen-activated protein kinases (MAPKs) revealed no differences in the contents of total p38-MAPK in both ventricles between the IHA and normoxic control rats, whereas activation of p38-MAPK was decreased in the RV and moderately increased in the LV of IHA rats as compared to controls. Extracellular signal regulated kinase-2 (ERK-2) was partially up-regulated in the RV of IHA rats, and, in addition, expression of acidic fibroblast growth factor (aFGF), a potential activator of ERK cascade, was also significantly increased. In contrast, expression of ERKs in the LV as well as their activities in both ventricles, were not affected by IHA hypoxia. Differential effects of IHA hypoxia on c-Jun-N-terminal protein kinases (JNKs) in the RV and LV were also observed. As compared with the controls, total content of JNKs was increased in the RV of the IHA rats, while expression of JNKs in the LV was down-regulated. IHA hypoxia changed neither total levels of Akt kinase in both RV and LV, nor Akt kinase activity in the RV. However, increased levels of activated phospho-Akt kinase were found in the LV of IHA rats. The results demonstrate that adaptation of rat hearts to chronic IHA hypoxia is associated with disctinct changes in the levels and/or activation of several regulatory proteins in two ventricles. The latter could be attributed to both myocardial remodeling and cardioprotection induced by chronic hypoxia.     

Influence of gramicidin S on cardiac membrane Ca2+/Mg2+ ATPase activities and contractile force development

The effects of gramicidin S (GS), an antibiotic, on the rat heart membrane ATPases and contractile activity of the right ventricle strips were investigated. GS inhibited sarcolemmal Ca2+-stimulated ATPase (IC50 = 3 microM), Ca2+/Mg2+ ATPase which is activated by millimolar Ca2+ or Mg2+ (IC50 = 3.4 microM), and sarcoplasmic reticulum Ca2+-stimulated ATPase (IC50 = 6 microM). The type of inhibition for the sarcolemmal Ca2+/Mg2+ ATPase by GS was apparently uncompetitive, while that for Ca2+-stimulated ATPases in sarcolemma or sarcoplasmic reticulum was of mixed type. Other ATPases, including mitochondrial ATPase, sarcolemmal Na+-K+ ATPase, and myofibrillar ATPase, were not inhibited by this agent. GS also decreased the rat right ventricle maximum force development (half-maximal inhibitory concentration was 2-4 microM), maximum velocity of contraction, and maximum velocity of relaxation. The resting tension was increased by GS to over 200%. The contractile actions of GS were mostly irreversible upon washing the muscle 3 times over a 10-min period. Decreased Ca2+, Mg2+, Na+, K+ concentrations in the perfusate increased the effects of GS. These findings showed that GS was a potent inhibitor of divalent cation ATPases of heart sarcolemma and sarcoplasmic reticulum and it is suggested that these membrane effects may explain the cardiodepressant action of this agent.     

Exposure to intermittent high altitude induces different changes in adenylyl cyclase activity in hearts of young and adult Wistar rats

This study investigates changes of adenylyl cyclase activity in the heart of young and adult Wistar rats exposed to experimental conditions simulating high altitude hypoxia as a model for interpretation of some adaptive changes of adenylyl cyclase observed in human. The exposure of rats to intermittent high altitude (IHA) hypoxia (5000 m) showed significant adaptive changes. The right ventricular weight and the ratio of right/left ventricular weights of adult rats exposed to IHA were significantly increased when compared to appropriate controls; adaptive changes of cardiac adenylyl cyclase being dependent on the age of the animals. The isoprenaline-stimulated activity was higher in the left than in the right ventricle, and in both ventricles it was higher in young rats than in adult rats. When compared to controls, isoprenaline stimulation was decreased in the right ventricles of adapted young rats and, by contrast, it was increased in the left ventricles of adapted adult rats. This decrease and increase of adenylyl cyclase activity evoked by isoprenaline was paralleled by forskolin-induced adenylyl cyclase activity in these experimental groups. It seems therefore that the changes in the pattern of total adenylyl cyclase activity observed under IHA hypoxia may at least be partially explained by the changes of beta-adrenergic receptor susceptibility following IHA hypoxia.     

Exposure to Intermittent High Altitude Induces Different Changes in Adenylyl Cyclase Activity in Hearts of Young and Adult Wistar Rats

Abstract

This study investigates changes of adenylyl cyclase activity in the heart of young and adult Wistar rats exposed to experimental conditions simulating high altitude hypoxia as a model for interpretation of some adaptive changes of adenylyl cyclase observed in human. The exposure of rats to intermittent high altitude (IHA) hypoxia (5000 m) showed significant adaptive changes. The right ventricular weight and the ratio of right/left ventricular weights of adult rats exposed to IHA were significantly increased when compared to appropriate controls; adaptive changes of cardiac adenylyl cyclase being dependent on the age of the animals. The isoprenaline‐stimulated activity was higher in the left than in the right ventricle, and in both ventricles it was higher in young rats than in adult rats. When compared to controls, isoprenaline stimulation was decreased in the right ventricles of adapted young rats and, by contrast, it was increased in the left ventricles of adapted adult rats. This decrease and increase of adenylyl cyclase activity evoked by isoprenaline was paralleled by forskolin‐induced adenylyl cyclase activity in these experimental groups. It seems therefore that the changes in the pattern of total adenylyl cyclase activity observed under IHA hypoxia may at least be partially explained by the changes of beta‐adrenergic receptor susceptibility following IHA hypoxia.     

K-FGF mediated transformation and induction of metastatic potential involves altered ornithine decarboxylase and S-adenosylmethionine decarboxylase expression – role in cellular invasion

Adult male Wistar rats were exposed to intermittent high altitude hypoxia of 7000 m simulated in a hypobaric chamber for 8 h/day, 5 days a week; the total number of exposures was 25. The concentration of individual phospholipids and their fatty acid (FA) profile was determined in right (RV) and left (LV) ventricles. Adaptation to hypoxia decreased the concentration of diphosphatidylglycerol (DPG) in hypertrophied RV by 19% and in non-hypertrophied LV by 12% in comparison with normoxic controls. Chronically hypoxic hearts exhibited lower phospholipid n-6 polyunsaturated FA (PUFA) content mainly due to decreased linoleic acid (18:2n-6), which was opposed by increased n-3 PUFA mainly due to docosahexaenoic acid (22:6n-3) in phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). The content of arachidonic acid (20:4n-6) was unchanged in total phospholipids, but in PC it was increased in both ventricles (by 22%) and in PE decreased in LV only (by 20%). Chronic hypoxia increased the un-saturation index of PC and PE in both ventricles. The content of monounsaturated FA (MUFA) was increased and 18:2n-6 decreased in DPG. The proportion of saturated FA was increased in PC and PI of hypoxic RV but not LV. The FA composition of phosphatidylserine was not altered in hypoxic ventricles. It is concluded that chronic hypoxia led to only minor changes in individual phospholipid concentration in rat ventricular myocardium, but markedly altered their FA profile. These changes, in particular the greater incorporation of n-3 PUFA into phospholipids and increased un-saturation index, may lead to a better preservation of membrane integrity and thereby contribute to improved ischemic tolerance of chronically hypoxic hearts.     

慢性缺氧对大鼠左右心室功能、心肌肌原纤维Ca~（2＋），Mg~（2＋）－ATP

模拟５０００ｍ中度缺氧时,大鼠右室功能显著加强,而左室功能加强不显著;左右心室肌原纤维Ｃａ２＋,Ｍｇ２＋－ＡＴＰ酶活性下降,肌球蛋白同功酶Ｖ２和Ｖ３百分含量增加,Ｖ１百分含量减少。８０００ｍ重度缺氧时,右室功能减弱,但无统计学意义,左室功能减弱有显著性;ＡＴＰ酶活性和同功酶的变化超过５０００ｍ组。此外,右室ＡＴＰ酶活性与ＰＡＰ呈反比且有显著性,左室ＡＴＰ酶活性与ＣＡＳＰ虽也呈反比但无显著性;右室同功酶Ｖ３百分含量与ＰＡＰ呈正比,左室同功酶Ｖ３百分含量与ＣＡＳＰ不呈比例。上述结果表明,因短期突发严重缺氧引起的心肌供氧不足对左心室心肌的直接损伤作用大于右心室心肌。     

Stimulation of sodium-calcium exchange by cholesterol incorporation into isolated cardiac sarcolemmal vesicles

Modification of the cholesterol content of highly purified cardiac sarcolemma from dog ventricles was accomplished by incubation with phosphatidylcholine liposomes containing various amounts of cholesterol. The degree of cholesterol enrichment could be varied by changing the liposomal cholesterol/phospholipid ratio or varying the liposome-membrane incubation time. Na+-Ca2+ exchange measured in cholesterol-enriched sarcolemmal vesicles was increased up to 48% over control values. The stimulation of Na+-Ca2+ exchange was associated with an increased affinity of the exchanger for Ca2+ (Km = 17 microM compared with Km = 22 microM for control preparations). Na+-Ca2+ exchange measured in cholesterol-depleted membrane preparations was decreased by 15%. This depressed activity was associated with a decreased affinity of the exchanger for Ca2+ (Km = 27 microM). These changes were not due to either a change in membrane permeability to Ca2+ or an increase in the amount of Ca2+ bound to sarcolemmal vesicles. The stimulating effect of cholesterol enrichment was specific to the Na+-Ca2+ exchange process since sarcolemmal Ca2+-Mg2+ ATPase activity was depressed 40% by cholesterol enrichment. Further, K+-p-nitrophenylphosphatase and Na+-K+ ATPase activities were depressed in both cholesterol-depleted and cholesterol-enriched sarcolemmal vesicles. In situ oxidation of membrane cholesterol completely eliminated Na+-Ca2+ exchange. These results suggest that cholesterol is intimately associated with Na+-Ca2+ exchange and may interact with the exchange protein and modulate its activity.     

Inhibitory action of opioid peptides on ouabain-sensitive Na+-K+ and Ca2+-dependent ATPase activities in bovine cardiac sarcolemma

The present study demonstrates that morphine (10(-6) and 10(-5) M), methionine-enkephalin or leucine-enkephalin (10(-10), 10(-8), and 10(-6) M) were able to inhibit significantly, in a dose-dependent manner, both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. The inhibitory action of these opioids on the two ATPases was not antagonized by preincubation with naloxone (10(-6) M). Naloxone alone (10(-8), 10(-6) and 10(-5) M) did not affect both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. Heat-denatured methionine-enkephalin (10(-6) M) or leucine-enkephalin (10(-6) M) also unaffected both the ATPases. The possibility is also discussed that opioid peptides may regulate myocardial contractility by modulating the movement of ions across the heart sarcolemma.     

Regulation of cardiac sarcolemmal Ca2+ channels and Ca2+ transporters by thyroid hormone

In order to examine the regulatory role of thyroid hormone on sarcolemmal Ca²⁺-channels, Na⁺–Ca²⁺ exchange and Ca²⁺-pump as well as heart function, the effects of hypothyroidism and hyperthyroidism on rat heart performance and sarcolemmal Ca²⁺-handling were studied. Hyperthyroid rats showed higher values for heart rate (HR), maximal rates of ventricular pressure development+(dP/dt)max and pressure fall–(dP/dt)max, but shorter time to peak ventricular pressure (TPVP) and contraction time (CT) when compared with euthyroid rats. The left ventricular systolic pressure (LVSP) and left ventricular end-diastolic pressure (LVEDP), as well as aortic systolic and diastolic pressures (ASP and ADP, respectively) were not significantly altered. Hypothyroid rats exhibited decreased values of LVSP, HR, ASP, ADP, +(dP/dt)max and –(dP/dt)max but higher CT when compared with euthyroid rats; the values of LVEDP and TPVP were not changed. Studies with isolated-perfused hearts showed that while hypothyroidism did not modulate the inotropic response to extracellular Ca²⁺ and Ca²⁺ channel blocker verapamil, hyperthyroidism increased sensitivity to Ca²⁺ and decreased sensitivity to verapamil in comparison to euthyroid hearts. Studies of [³H]-nitrendipine binding with purified cardiac sarcolemmal membrane revealed decreased number of high affinity binding sites (B_max) without any change in the dissociation constant for receptor-ligand complex (K_d) in the hyperthyroid group when compared with euthyroid sarcolemma; hypothyroidism had no effect on these parameters. The activities of sarcolemmal Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake and ouabain-sensitive Na⁺–K⁺ ATPase were decreased whereas the Mg²⁺-ATPase activity was increased in hypothyroid hearts. On the other hand, sarcolemmal membranes from hyperthyroid samples exhibited increased ouabain-sensitive Na⁺–K⁺ ATPase activity, whereas Ca²⁺-stimulated ATPase, ATP-dependent Ca²⁺ uptake, and Mg²⁺-ATPase activities were unchanged. The V_max and K_a for Ca²⁺ of cardiac sarcolemmal Na⁺–Ca²⁺ exchange were not altered in both hyperthyroid and hypothyroid states. These results indicate that the status of sarcolemmal Ca²⁺-transport processes is regulated by thyroid hormones and the modification of Ca²⁺-fluxes across the sarcolemmal membrane may play a crucial role in the development of thyroid state-dependent contractile changes in the heart.     

Sarcolemmal Na+-Ca2+ exchange and Ca2+-pump activities in cardiomyopathies due to intracellular Ca2+-overload

In order to identify defects in Na⁺-Ca²⁺ exchange and Ca²⁺-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na⁺-dependent Ca²⁺ uptake, Na⁺-induced Ca²⁺ release, ATP-dependent Ca²⁺ uptake and Ca²⁺-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na⁺-dependent Ca²⁺ uptake, ATP-dependent Ca²⁺ uptake and Ca²⁺-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na⁺-induced Ca²⁺-release. Similar results were obtained in Ca²⁺-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca²⁺ following a 5 min perfusion with Ca²⁺-free medium. Although a 2 min reperfusion of the Ca²⁺-free perfused hearts depressed sarcolemmal Ca²⁺-pump activities without any changes in Na⁺-induced Ca²⁺-release, Na⁺-dependent Ca²⁺ uptake was increased. These results indicate that alterations in the sarcolemmal Ca²⁺-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca²⁺ overload.     

Response of rat heart membranes and associated ion-transporting ATPases to dietary lipid

The effects of different dietary fat intake on the lipid composition and enzyme behaviour of sarcolemmal (Na+ + K+)ATPase and sarcoplasmic reticulum Ca2+-ATPase from rat heart were investigated. Rat diets were supplemented with either sunflower seed oil (unsatd./satd. 5.6) or sheep kidney fat (unsatd./satd. 0.8). Significant changes in the phospholipid fatty acid composition were observed in both membranes after 9 weeks dietary lipid treatment. For both membranes, the total saturated/unsaturated fatty acid levels were unaffected by the dietary lipid treatment, however the proportions of the major unsaturated fatty acids were altered. Animals fed the sunflower seed oil diet exhibited an increase in n-6 fatty acids, including linoleic (18:2(n-6] and arachidonic (20:4(n-6] while the sheep kidney fat dietary rats were higher in n-3 fatty acids, principally docosahexaenoic (22:6), with the net result being a higher n-6/n-3 ratio in the sunflower seed oil group compared to sheep kidney fat dietary animals. Fluorescence polarization indicated that the fluidity of sarcoplasmic reticular membrane was greater than that of sarcolemmal membrane, with a dietary lipid-induced decrease in fluidity being observed in the sarcoplasmic reticular membrane from sheep kidney fat dietary animals. Despite these significant changes in membrane composition and physical properties, neither the specific activity nor the temperature-activity relationship (Arrhenius profile) of the associated ATPases were altered. These results suggest that with regard to the parameters measured in this study, the two ion-transporting ATPases are not modulated by changes which occur in the membrane lipid composition as a result of the diet.     

Relationship between mechanical dysfunction and depression of sarcolemmal Ca2+-pump activity in hearts perfused with oxygen free radicals

Although in vitro studies have shown that oxygen free radicals depress the sarcolemmal Ca²⁺-pump activity and thereby may cause the occurrence of intracellular Ca²⁺ overload for the genesis of contractile failure, the exact relationship between changes in sarcolemmal Ca²⁺-pump activity and cardiac function due to these radicals is not clear. In this study we examined the effects of oxygen radicals on sarcolemmal Ca²⁺ uptake and Ca²⁺-stimulated ATPase activities as well as contractile force development by employing isolated rat heart preparations. When hearts were perfused with medium containing xanthine plus xanthine oxidase, the sarcolemmal Ca²⁺-stimulated ATPase activity and ATP-dependent Ca²⁺ accumulation were depressed within 1 min whereas the developed contractile force, rate of contraction and rate of relaxation were increased at 1 min and decreased over 3–20 min of perfusion. The resting tension started increasing at 2 min of perfusion with xanthine plus xanthine oxidase. Catalase showed protective effects against these alterations in heart function and sarcolemmal Ca²⁺-pump activities upon perfusion with xanthine plus xanthine oxidase whereas superoxide dismutase did not exert such effects. The combination of catalase and superoxide dismutase did not produce greater effects in comparison to catalase alone. These results are consistent with the view that the depression of heart sarcolemmal Ca²⁺ pump activities may result in myocardial dysfunction due to the formation of hydrogen peroxide and/or hydroxyl radicals upon perfusing the hearts with xanthine plus xanthine oxidase.     

Effect of altitude hypoxia on ATPase activity in the brain of rats of different ages.

In experiments on 5-day-old and adult rats of both sexes, the authors investigated Na+--K+-stimulated and Mg2+-dependent ATPase activity in the cerebral cortex, subcortical formations and the medulla oblongata. They studied the effect of 20 min acute altitude hypoxia corresponding to either 7,000 or 9,000 m, in a thermostable chamber (30 degrees C). ATPase activity was found to increase during ontogenesis -- this being the greatest in cortical tissue and the least in the medulla oblongata. Hypoxia corresponding to 7,000 m altitude significantly depressed total ATPase activity in 5-day-old rats, but significantly stimulated it in adult animals. Changes in Na+--K+-stimulated ATPase activity played the major role in these changes. Hypoxia corresponding to 9,000 m altitude likewise depressed total ATPase activity in 5-day-old rats and to practically the same extent as moderate hypoxia (7,000 m). In adult rats, marked hypoxia (9,000 m) significantly reduced only Mg2+-dependent ATPase activity. Mg2+ activity rose during ontogenesis to a lesser degree than Na+--K+-stimulated ATPase and the reciprocal ratio of these ATPase and the reciprocal ratio of these ATPase activities, in the given parts of the brain, fell progressively in adult animals to values close to 1.     

Effects of chronic swimming training on cardiac sarcolemmal function and composition

Cardiac contractile function is dependent on the integrity and function of the sarcolemmal membrane. Swimming exercise training is known to increase cardiac contractile performance. The purpose of the present study was to examine whether a swimming exercise program would alter sarcolemmal enzyme activity, ion flux, and composition in rat hearts. After approximately 11 wk of exercise training, cardiac myosin and actomyosin Ca2+-adenosinetriphosphatase (ATPase) activity was significantly higher in exercised rat hearts than in sedentary control rat hearts. Glycogen content was increased in plantaris and gastrocnemius muscles from exercised animals as was succinic dehydrogenase activity in gastrocnemius muscle of exercised rats in comparison to sedentary rat preparations. Sarcolemmal vesicles were isolated from hearts of exercise-trained and control rats. Sarcolemmal Na+-K+-ATPase and K+-p-nitrophenylphosphatase activities, Na+-Ca2+ exchange, and passive Ca2+ binding did not differ between the two groups. ATP-dependent Ca2+ uptake and 5'-nucleotidase activity were elevated in the cardiac sarcolemmal vesicles isolated from exercised animals compared with sedentary control rats. Sarcolemmal phospholipid composition was not altered by the exercise training. Our results demonstrate that swimming training in rats does not affect most parameters of cardiac sarcolemmal function or composition. However, the elevated sarcolemmal Ca2+ pump activity in exercised rats may help to reduce intracellular Ca2+ and augment cardiac relaxation rates. The enhanced 5'-nucleotidase activity may stimulate adenosine production, which could affect myocardial blood flow. The present results further our knowledge on the subcellular response of the heart to swimming training in the rat.     

Effects of lanthanum on the heart sarcolemmal ATPase and calcium binding activities.

Effects of lanthanum on Ca2+-ATPase, Mg2+-ATPase, Na+-K+-ATPase, and calcium binding activities were studied in rat heart sarcolemma. Ten to 100 micrometers lanthanum depressed significantly the Ca2+-ATPase activity and 50--200 micrometers lanthanum inhibited the calcium binding activity. Lineweaver-Burk plots of the Ca2+-ATPase activity showed that the inhibition by lanthanum was competitive with calcium concentration. Neither Mg2+-ATPase nor Na+-K+-ATPase activities were affected by lanthanum when the assay medium contained 1 mM EDTA; however, in the absence of EDTA, these enzyme activities were significantly decreased by 10--100 micrometers lanthanum. Rat hearts perfused with HEPES buffer containing 0.5 mM lanthanum showed electron-dense deposits restricted to the outer cell surface and the sarcolemma obtained from these hearts also had the deposits, indicating that the membrane fraction isolated by the hypotonic shock--LiBr treatment method is of sarcolemmal origin. The Ca2+-ATPase activity of the sarcolemma isolated from lanthanum-perfused hearts, unlike the Mg2+-ATPase, Na+-K+-ATPase, and calcium binding activities, was significantly less than the control value. From these observations it is suggested that lanthanum may influence calcium movement across the sarcolemma by affecting sarcolemmal ATPase and calcium binding activities.     

Changes in myocardial contractile protein ATPases in chronically adrenalectomized rats with and without glucocorticoid replacement

Studies were conducted to examine the effects of chronic adrenalectomy (Adx) and adrenalectomy plus glucocorticoid replacement therapy on rat cardiac contractile protein ATPase activities. The Ca2+-dependent Mg-ATPase activity of myofibrils isolated from rat ventricles 3 weeks postadrenalectomy (Adx) was significantly decreased at all pCa2+ concentrations (P less than 0.01), compared to sham-operated (SO) rats. Similarly, Ca2+-, K+-EDTA, and actin-activated myosin ATPase activities of Adx rat hearts were markedly decreased below that of SO rats (P less than 0.01). Dexamethasone administration to Adx rats prevented the decrease of Ca2+- and K+-ATPase activities of myosin, but not of myofibrillar Ca2+-dependent Mg-ATPase or actin-activated myosin Mg-ATPase activities. These studies suggest that glucocorticoid insufficiency induced by adrenalectomy results in altered myocardial contractile protein ATPase activity which may underlie impaired cardiac performance.     

Stimulation of calcium pump activity in heart sarcolemma by timolol

The effects of beta-adrenergic blocking agents, timolol and atenolol (1-1000 microM), were studied on rat heart sarcolemmal ATPase and Ca2+ binding activities. Timolol, unlike atenolol, increased both Ca2+-stimulated ATPase and ATP-dependent Ca2+ binding; the maximal effects were seen at 1 microM concentration of timolol. Both timolol and atenolol did not alter the sarcolemmal Mg2+ ATPase and nonspecific Ca2+ binding activities. Sarcolemmal Ca2+-stimulated ATPase was also activated by concanavalin A (6-66 micrograms/mL) which is known to alter membrane fluidity; however, Mg2+ ATPase was unaffected by this agent. These results indicate that timolol may stimulate Ca2+ pump activity in heart sarcolemma by changing membrane fluidity in a manner similar to that of concanavalin A.     

Specific stimulation of heart sarcolemmal Ca2+/Mg2+ ATPase by concanavalin A

The effects of concanavalin A (Con A) on membrane Ca2+/Mg2+ ATPase activities as well as the characteristics of Con A binding were examined by employing rat heart sarcolemmal preparations. Con A stimulated the Ca2+ ATPase and Mg2+ ATPase activities in sarcolemma; maximal stimulation in these parameters was seen at a concentration of 10 micrograms/ml. The observed effects of Con A were blocked by alpha-methylmannoside. Sarcolemmal Na+-K+ ATPase and Ca2+-stimulated ATPase were not affected by Con A. Likewise, Con A did not alter the mitochondrial, sarcoplasmic reticular, and myofibrillar ATPase activities. Con A was found to bind to sarcolemma; alpha-methylmannoside prevented this binding. The Scatchard plot analysis of the data on specific Con A binding showed a straight line with a Kd of about 530 nM and a Bmax of 235 pmol/mg protein, thus indicating that there was only one kind of binding site for Con A in sarcolemma. These results suggest that Con A is a specific activator of the low affinity Ca2+/Mg2+ ATPase system in the heart sarcolemmal membrane.     

Effect of fish oil and vitamin E on ethanol-induced changes in membrane ATPases

We evaluated whether fish oil or vitamin E administration affected ethanol-induced changes in membrane ATPases. Male Wistar rats (225–250 g) were fed, through a gastric tube a liquid diet containing fish oil (25% of calories) and ethanol for one month. Another group of animals was given supplemental vitamin E (300 u/kg). In the pair-fed control animals, ethanol-derived calories were replaced with dextrose. The blood ethanol levels were maintained between 150 and 350 mg/dL. At sacrifice, the red cells were immediately washed with ice-cold saline, membranes were prepared and ATPases measured. These was no difference in the Na⁺K⁺ ATPase, Ca²⁺ ATPase and Mg²⁺ ATPase activities between the fish oil-dextrose and corn oil-dextrose groups. A decrease in Ca²⁺ ATPase and an increase in Na⁺K⁺ ATPase was seen with ethanol feeding; these change are similar to those seen in corn oil-ethanol fed rats. In contrast, Vitamin E administration prevented the ethanol-induced changes in ATPases. This observation provides support for the role of lipid peroxidation in alcohol-induced changes in cell membrane ATPase activities.