Type B monoamine oxidase and functions of Ca2+, Mg2+-dependent adenosinetriphosphatase in preparations from sarcoplasmic reticulum vesicles

Oxidative deamination of -phenylethylamine or benzylamine by type B monoamine oxidases (MAO) in preparations of sarcoplasmic reticulum vesicles from rabbit skeletal muscles is accompanied by inhibition both of active Ca²⁺ transport into the vesicles and of the activity of Ca²⁺, Mg²⁺-dependent ATPase, which is preventable by deprenil, a specific inhibitor of type B MAO. Aldehydes formed during enzymatic deamination of substrates of type B MAO may perhaps participate in the regulation of Ca²⁺, Mg²⁺-dependent ATPase, activity.Laboratory of Physicochemical Methods, Scientific-Research Institute for Biological Trials of Chemical Compounds, Ministry of the Medical Industry of the USSR. Laboratory or Biochemistry of Amines and Other Nitrogenous Compounds, Institute of Biological and Medical Chemistry, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Orekhovich.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 3, pp. 283–284, March, 1977.     

Effects of isoproterenol and suphan on the concentration of free calcium ions in isolated cardiomyocytes: a comparative study

Isoproterenol and suphan, two cardioactive drugs with different mechanisms of action, are studiedin vitro for their effects on calcium homeostasis in myocardial cells. Isoproterenol lowers the basal Ca²⁺ level in resting cardiomyocytes and potentiates its rise in these cells after their induction. Suphan stimulates reversible elevation of the diastolic Ca²⁺ concentration, causing increased calcium accumulation in the sarcoplasmic reticulum of cardiomyocytes. In anin vitro model of hypoxia, the Ca response to isoproterenol is significantly reduced, whereas that to dibutyryl cAMP is retained. The effect of suphan on the Ca²⁺ content of cardiomyocytes exposed to “chemical” hypoxia is 30–50% higher than its effect on the Ca²⁺ content of intact cells. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 8 pp. 170–172, August, 1996     

Ca2+ transport of the skeletal muscle sarcoplasmic reticulum during readaptation of rats after a 40-day load relief on the hind paws

The rate of Ca²⁺ accumulation in the sarcoplasmic reticulum of the skeletal muscle (m. gastrocnemius lateralis, m. vastus medialis, andm. soleus) is studied in rats under conditions of functional off-loading of the hind paws (suspending animals by the tail). The rate of Ca²⁺ transport in the sarcoplasmic reticulum is shown to be stepped up in all these muscles. In the sarcoplasmic reticulum ofm. gastrocnemius lateralis andm. vastus medialis the Ca²⁺ transport rate reliably drops, which does not occur inm. soleus. During a 2-week period of readaptation of animals suspended for 40 days, the Ca²⁺-transporting function of them. soleus sarcoplasmic reticulum gradually recovers to reach the control values, whereas the time course of recovery of Ca²⁺-pump activity in the sarcoplasmic reticulum ofm. gastrocnemius lateralis andm. vastus medialis has a phasic pattern. Translated fromByulleten' Eksperimental'noi Biologii i Meditsity, Vol. 118, N ^o 12, pp. 591–595, December, 1994 Presented by A. I. Grigor'ev, Member of the Russian Academy of Medical Sciences     

Ca2+ transport in the myocardial sarcoplasmic reticulum of rats during antiorthostatic off-loading and during readaptation

The rate of Ca²⁺ accumulation in the myocardial sarcoplasmic reticulum is studied in experiments on rats under conditions of hind paw functional off-loading by suspending animals by the tail for 1 to 40 days, as well as during a 2-week period of readaptation after a 40-day load relief. The rate of Ca²⁺ transport in the myocardial sarcoplasmic reticulum reliably drops (by 33%) after 40 days of suspension. At earlier stages of off-loading Ca-pump activity in the sarcoplasmic reticulum does not change reliably. After resumption of the loads in animals suspended for 40 days, the transporting function of the myocardial sarcoplasmic reticulum rapidly reverts to the control level, which is indicative of a reversible pattern of load relief-induced changes in the rate of Ca²⁺ transport. Translated fromByulleten' Eksperimental'noi Biologii i Meditsity, Vol. 118, N ^o 12, pp. 596–599, December, 1994 Presented by G. N. Kryzhanovskii, Member of the Russian Academy of Medical Sciences     

The role of cytoplasmic factors in stabilization of Ca2+-transporting function of myocardial sarcoplasmic reticulum in rats during adaptation to stress

Acute stress reduces and adaptation to stress enhances thermal resistance of Ca²⁺ pump of the sarcoplasmic reticulum fraction. Soluble cytoplasmic factors increase the rate of Ca²⁺ transport into myocardial sarcoplasmic reticulum and its thermal resistance in the stressed, stress-adapted, and control rats, the activating effect being most pronounced during acute stress. Structural and functional mechanisms underlying the protective effect of soluble cytoplasmic factors on membrane-bound enzymes are discussed. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 2, pp. 155–159, February 1999     

Mechanism of action of the new cardiotonic suphan on calcium exchange in cardiomyocytes

Effects of suphan, a new cardiotonic agent containing succinyl tryptophan, on the entry of Ca²⁺ into rat cardiomyocytes, its intracellular compartmentalization, and its exit from these cells were evaluatedin vitro. It was found that the recorded sulfan-induced rise of intracellular calcium was due to Ca²⁺ entering the cell via L-type calcium channels, and that a reversible reduction of its concentration in the sarcoplasm occurred through its accumulation in the sarcoplasmic reticulum and was blocked by the specific Ca²⁺-ATPase inhibitor thapsigargin (10 μM). Suphan did not alter the activity of Na⁺/Ca²⁺ exchange in a concentration range of 5–150 μg/ml. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 7, pp. 57–59, July, 1996     

Initiation of apoptosis in hepatocytes during prolonged arterial hypotension and postresuscitation period

An increase in activity of Ca²⁺, Mg²⁺-dependent endonucleases on the second hour of hypotension coincided with the presence of DNA fragments in agarose gel. A correlation was established between the duration of hypotension, Ca²⁺, Mg²⁺-dependent endonuclease activity, and intensity of nuclear DNA fragmention. Apopotosis of hepatocytes is triggered during ischemia and develops during reperfusion. Translated fromByulleten' Eksperimental'noi Biologii i Meditisiny, Vol. 125, No. 3, pp. 285–288, March, 1998     

Effect of activation of Ca2+, Mg2+-dependent endonuclease on proliferative response of human peripheral blood lymphocytes

Activity of Ca²⁺, Mg²⁺-dependent endonuclease in human peripheral blood mononuclears is studied. Intact cells exhibit extremely low activity of the enzyme. Treatment with the synthetic hexapeptide imunofan considerably stimulates endonuclease activity in mononuclears. This activation does not depend on additional protein synthesis. An 1-h incubation in the presence of cycloheximide also activates Ca²⁺, Mg²⁺-dependent endonuclease. These data suggest that imunofant and/or cycloheximide activate the apoptotic cascade. This leads to activation of endonuclease, which is not synthesizedde novo but persists in the cell in the form of inactive precursor. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 123, No. 5, pp. 535–537, May, 1997     

Adaptation to periodic hypoxia and a diet supplemented with polyunsaturated class ω-3 fatty acids enhance the resistance of Ca2+ transport in the myocardial sarcoplasmic reticulum to free-radical oxidation

The relationship between the level of accumulation of lipid peroxidation products and the status of the Ca²⁺-transporting system in the sarcoplasmic reticulum of the rat myocardium is studied against the background of two cardioprotective factors, namely adaptation to periodic hypoxia and a diet enriched in polyunsaturated fatty acids of the ω-3 class. It is shown that the diet leads to an increase of level of lipid peroxidation products by 1.8 times in the heart and by 19 times in the liver, whereas a adaptation has no effect on the level of lipid peroxidation products in either of these organs. At the same time, the combined action of both factors considerably enhances the resistance of the myocardial Ca²⁺-transporting system to free radical-induced oxidation. Inin vitro experiments it is shown that adaptation to periodic hypoxia results in a more than twofold deceleration of Ca²⁺ transport inhibition during the oxidation induction by the Fe²⁺/ascorbate system; the diet causes a 3.5-fold deceleration of such inhibition. The results show that the accumulation of a high level of lipid peroxidation products is not always followed by damage to the Ca²⁺-transporting system in the myocardial sarcoplasmic reticulum. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 7, pp. 42–45, July, 1995 Presented by G. N. Kryzhanovskii, Member of the Russian Academy of Medical Sciences     

Chaperone activity of α-crystallin in relation to the sarcoplasmic reticulum Ca2+ pump of skeletal muscles in stress and adaptation

α-Crystallin, an endogenous low-molecular-weight protein with chaperone activity, exerted protective effects on membrane systems of Ca²⁺ transport into the sarcoplasmic reticulum of skeletal muscles. Protective action of α-crystallin depended on the body state. This effect was not observed in the control and after adaptation to stress, while after stress, especially against the background of adaptation, α-crystallin increased the rate of Ca²⁺ transport into the sarcoplasmic reticulum and thermal resistance of Ca²⁺ pump. The mechanisms of α-crystallin activation during stress are discussed. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 9, pp. 279–282, September, 1999     

Opposite effect of adaptation to physical exercise on myocardium and skeletal muscle. Ca-transporting system of the sarcoplasmic reticulum and antioxidant defense enzymes

Adaptation to physical exercise was achieved via 60-min sessions of swimming at 32°C for 45 days, the duration of swimming being increased from 15 to 60 min during the first 14 days. Under these conditions, against the background of reduced catalase and superoxide dismutase activity the Ca-transporting system of the sarcoplasmic reticulum in the heart is shown to work more effectively: Ca²⁺ transport is characterized by a higher initial rate and is inactivated 1.5 times more slowly byin vitro-induced lipid peroxidation and not inhibited by high concentrations of free Ca²⁺. In the skeletal muscle, on the other hand, catalase and superoxide dismutase activity rise, but this does not improve the functioning of the Ca pump: the initial rate of Ca²⁺ transport drops, its resistance to autooxidation is not increased in comparison with the control, and the resistance of the Ca²⁺-transporting system to the inhibiting influence of free Ca²⁺ is lowered. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, No. 6, pp. 623–628, June, 1996     

Adaptation to physical exercise increases expression of Ca-ATPase gene in myocardial sarcoplasmic reticulum

Gene expression of the key enzyme of the myocardial sarcoplasmic reticulum Ca²⁺-pump, SERCA-2a isoform was assayed in rats during adaptation to physical exercise (forced swimming). The expression was measured by Northern blot hybridization with subsequent densitometry of the autoradiograms. The signal of mRNA encoding SERCA-2a was referenced to the mRNA signals of marker proteins (S4 and S9 ribosomal proteins, cytoskeletal β-actin and glyceraldehyde-3-phosphate dehydrogenase). The SERCA-2a gene expression gradually increased during adaptation as evidenced by the increased content of SERCA-2a mRNA in particular higher intensity (optical density) of the mRNA signals in autoradiograms. The adaptation-induced increase in the power of the sarcoplasmic reticulum Ca²⁺-pump can be attributed to activated synthesis and accumulation of SERCA-2a isoform. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 7, pp. 24–28, July, 1999     

The effect of delta-sleep-inducing peptide on the Ca-transporting system of the sarcoplasmic reticulum and activity of the myocardial antioxidant enzymes

It is demonstrated that immobilization stress against the background of lowered catalase activity impairs the function of the sarcoplasmic reticulum Ca pump, particularly at high Ca²⁺ levels. the membranes of intracellular Ca²⁺ depots are destroyed much more rapidly than in the control, which results in Ca²⁺ release. Administration of delta sleep-inducing peptide to control animals results in a 30% increase in catalase activity for an unchanged level of superoxide dismusase and markedly improves the function of the Ca-transporting system at elevated levels of free Ca²⁺. A long-term stress after administration of the peptide not only causes no damage to the Ca-transporting system but actually increases its efficiency (compared with the control) at a high catalase level. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N ^o 3, pp. 248–251, March, 1996 Presented by G. N. Kryzhanovskii, Member of the Russian Academy of Medical Sciences     

Effect of emergent and long-term adaptation to physical strength on the resistance of Ca-transporting system of myocardial sarcoplasmic reticulum

Experiments were carried out on rats adapted to physical exercise (on the next day after completion of 4, 11, 15, and 30 swimming sessions). Catalase and superoxide dismutase activities were similar in all rats. The resistance of Ca transport into sarcoplasmic reticulum to high Ca²⁺ concentrations and autooxidaton increased starting from 4 swimming sessions, and to thermal inactivation from 11 sessions; the maximum resistance was attained after 15 sessions 1.5- to 2-fold surpassing the initial level. Maximum initial rate of Ca²⁺-transport (155% of the control) was observed after 30 swimming sessions. In acute physical strength and at the initial stages of adaptation (4 swimming sessions) functional properties of myocardial Ca-transporting system were preserved under optimal conditions, but can be readily disturbed by adverse factors. Translatedfrom Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 125, No. 1, pp. 40–44, January, 1998 Original     

Ca-dependent ATPase activity and lipid peroxidation in the microsome fraction of renal medulla after thermal ischemia with and without α-tocopherol protection

Thermal ischemia of rat kidneys for 30 min induces lipid peroxidation with simultaneous activation of Ca-dependent ATPase in microsomes. In the presence of the channel-forming antibiotic alamethicin this activity decreases, indicating an increased passive permeability of the membrane vesicles for Ca²⁺ and ATP with a decrease in the true activity of the enzyme after ischemia. α-Tocopherol reduces the intensity of lipid peroxidation in the microsome fraction isolated from kidneys after thermal ischemia and protects ATPase activity in the presence and absence of alamethicin in the incubation medium. It is suggested that peroxidation of membrane phospholipids activated by thermal ischemia is one of the causes of decreased true activity of Ca-dependent ATPase and increased passive permeability of the kidney membranes for Ca²⁺ and ATP. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 9, pp. 289–291, September, 1997     

Ca-transporting system of the left ventricular sarcoplasmic reticulum in the rat heart and damage to its membrane during ischemia and reperfusion

Ischemia and reperfusion of various duration are shown to result in a nonlinear increase in the level of free Ca in myocardial homogenates. A striking dissociation has been observed in the effect of ischemia and reperfusion on the rate of Ca transport in the sarcoplasmic reticulum, on the one hand, and the permeability of its membranes on the other. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, N ^o 2, pp. 130–135, February, 1994     

Time resolved kinetics of the guinea pig Na–Ca exchanger (NCX1) expressed in Xenopus oocytes: voltage and Ca2+ dependence of pre-steady-state current investigated by photolytic Ca2+concentration jumps

Kinetic properties of the Na–Ca exchanger (guinea pig NCX1) expressed in Xenopus oocytes were investigated by patch clamp techniques and photolytic Ca²⁺ concentration jumps. Current measured in oocyte membranes expressing NCX1 is almost indistinguishable from current measured in patches derived from cardiac myocytes. In the Ca–Ca exchange mode, a transient inward current is observed, whereas in the Na–Ca exchange mode, current either rises to a plateau, or at higher Ca²⁺ concentration jumps, an initial transient is followed by a plateau. No comparable current was observed in membrane patches not expressing NCX1, indicating that photolytic Ca²⁺ concentrations jumps activate Na–Ca exchange current. Electrical currents generated by NCX1 expressed in Xenopus oocytes are about four times larger than those obtained from cardiac myocyte membranes enabling current recording with smaller concentration jumps and/or higher time resolution. The apparent affinity for Ca²⁺ of nonstationary exchange currents (0.1 mM) is much lower than that of stationary currents (6 μM). Measurement of the Ca²⁺ dependence of the rising phase provides direct evidence that the association rate constant for Ca²⁺ is about 5 × 10⁸ M⁻¹ s⁻¹ and voltage independent. In both transport modes, the transient current decays with a voltage independent but Ca²⁺-dependent rate constant, which is about 9,000 s⁻¹ at saturating Ca²⁺ concentrations. The voltage independence of this relaxation is maintained for Ca²⁺ concentrations far below saturation. In the Ca–Ca exchange mode, the amount of charge translocated after a concentration jump is independent of the magnitude of the jump but voltage dependent, increasing at negative voltages. The slope of the charge–voltage relation is independent of the Ca²⁺ concentration. Major conclusions are: (1) Photolytic Ca²⁺ concentration jumps generate current related to NCX1. (2) The dissociation constant for Ca²⁺ at the cytoplasmic transport binding site is about 0.1 mM. (3) The association rate constant of Ca²⁺ at the cytoplasmic transport sites is high (5 × 10⁻⁸ M⁻¹s⁻¹) and voltage independent. (4) The minimal five-state model (voltage independent binding reactions, one voltage independent conformational transition and one very fast voltage dependent conformational transition) used before to describe Ca²⁺ translocation at saturating Ca²⁺ concentrations is valid for Ca²⁺ concentrations far below saturation.     

Cytochemical localization of Ca2+-ATPases and demonstration of ATP-dependent calcium sequestration in giant smooth muscle fibres of Beroe

Summary A cytochemical analysis of the mechanisms underlying cytosolic calcium regulation was undertaken in the giant smooth muscle fibres of the marine invertebrate Beroe. The ability of the sarcoplasmic reticulum to accumulate Ca²⁺ was demonstrated on living skinned single cells. In the presence of oxalate, and physiological concentrations of Ca²⁺, calcium oxalate crystals were formed in the lumen of tubules and cisternae of the sarcoplasmic reticulum. The subcellular distribution of Ca^2–-ATPase was studied with a cytochemical technique; a dense precipitate resulting from Ca²⁺-ATPase activity was found on the plasma membrane, on the membranes of tubules and cisternae of the sarcoplasmic reticulum, and in mitochondria.     

Effects of bioglycans isolated from birch fungiinonotus obliquus on electric activity of venous sinus cells in frog heart

Bioglycans isolated from chaga in a concentration of 0.0001% reduced frequency of action potential in venous sinus cells of frog heart during the first 15–30 min of exposure, then this parameter increased by 10% per hour over 3.5 h, and was 41±3 min⁻¹ from the 4th to the 20th hour of incubation. The frequency of action potentials in heart strips in the chaga extract was 40% higher than in Ringer's solution. The effect of chaga bioglycan is probably associated with adsorption on myocyte membranes. Binding of Ca²⁺ to bioglycans observed during the first 30 min inhibited efflux of intracellular Ca²⁺. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 9, pp. 264–266, September, 1999