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V A Saks

Publications and source records attributed to V A Saks.

At least 19 recordsLinked to original sources
PubMed1992

[Molecular and cellular aspects of the cardioprotective mechanism of phosphocreatine].

The present state of investigations on molecular and cellular mechanisms of cardioprotective effects of phosphocreatine (PCr) is reviewed. The protective effect of PCr is manifested as significant improvement of heart contractile function recovery, lowering of diastolic pressure elevation and myocardial enzymes release during postischemic reperfusion as well as better preservation of high energy phosphates in comparison with control. Data from multidisciplinary studies using physico-chemical, physiological, pharmacological etc. approaches suggest that one of the key mechanisms of PCr action is its interaction with the sarcolemmal membrane. The authors own data obtained with the use of spin-labeled ESR-probe incorporated into the isolated sarcolemmal vesicles provide direct evidence in favor of the ordering effect of PCr sarcolemmal phospholipid packing with essential involvement of Ca2+ ions. PCr transform membrane phospholipids into more structured gel-like state. The results of biomedical studies suggest that the mechanism of this protective action is complex and includes at least four components: 1) inhibition of lysophosphoglyceride accumulation in the ischemic myocardium and preservation of cardiac cell sarcolemma structure via zwitterionic interaction with PCr molecules; ii) extracellular action consisting in inhibition of platelet aggregation via ADP removal in the extracellular creatine kinase reaction and increasing plasticity of red blood cells; iii) PCr penetration into cells maintenance of high local ATP levels is possible; iiii) inhibition of adenine nucleotide degradation at the step of 5'-nucleotidase reaction in cardiac cell sarcolemma.

Animals↗
PubMed1992

[Energy metabolism and contractile function of the heart in diabetic cardiomyopathy: effect of ischemia and reperfusion].

Physiological parameters, rates of mitochondrial respiration, high energy phosphate levels and creatine phosphokinase (CPK) activity were investigated in the hearts from control and alloxan-induced diabetic rabbits before and after 40-min total ischemia and reperfusion. Diabetic hearts demonstrated significant decreases in the rates of contraction (+dP/dt) and relaxation (-dP/dt), heart rates and cardiac work compared to control hearts. Determination of mitochondrial respiration rates in saponin-skinned fibers showed a low mitochondrial respiratory function in diabetic hearts. It was found that the ATP and ADP levels and the total and mitochondrial isoenzyme activities of CPK in diabetic hearts were lowered in comparison with control. A post-ischemic recovery of cardiac performance for diabetic hearts was better than in controls. After reperfusion diabetic hearts had increased ATP levels. The data obtained demonstrate some abnormalities of both cardiac performance and energy metabolism in the hearts of diabetic animals and a decreased sensitivity of the latter to ischemic injury.

Adenosine Diphosphate↗
PubMed1992

[The role of calcium ions in the molecular mechanism of the protective mechanism of exogenous phosphocreatine].

The role of Ca2+ in the manifestation of the cardioprotective effect of phosphocreatine (PCr) on the ischemic myocardium was studied in isolated rat hearts perfused by the Langendorf method. Under ischemic cardiac arrest induced by a Ca(2+)-free perfusing solution PCr had no protective effect on the ischemic myocardium. PCr accelerated the postischemic restoration of contractility of hearts perfused with a solution containing 0.5 and 1.2 mM Ca2+. The structural analog of PCr, phosphoarginine, possessing a Ca(2+)-binding capacity similar to that of PCr, had no protective effect. The effects of PCr and Ca2+ on the package of sarcolemmal vesiculate lipids were studied by ESR spectroscopy. PCr induced a more dense package of membrane phospholipids at weakly acidic and neutral values of pH (but not at pH 8.5). Although at pH 5.5 Ca2+ did not affect the membrane structure, it potentiated the effect of PCr on sarcolemmal phospholipids. Thus, the protective effect of PCr on the ischemic myocardium is not linked with its ability to bind Ca2+; however, Ca2+ is an indispensable component of the mechanism underlying the protective effect of PCr on the ischemic myocardium.

Animals↗
PubMed1992

[Quantitative relationship between ischemic heart disease and parameters of energy metabolism].

The relationship between coronary heart disease, postischemic work recovery and tissue ATP levels as well as mitochondrial respiration rates were studied. Respiration of mitochondria was assessed without their isolation by using a novel method applying skinned fibers in physiological saline. The maximal mitochondrial respiration rates were unchanged during 35 min of normothermic ischemia in St. Thomas Hospital cardioplegic solution in the subsequent 30 min aerobic reperfusion period. A reversible increase in the basal respiration and a decrease in creatine-stimulated oxygen uptake were observed. Thus, the combined determination of mitochondrial respiration in situ in skinned cardiac fibers and tissue ATP may be a useful approach to studies of the pathogenesis of cardiac diseases.

Adenosine Triphosphate↗
PubMed1992

[Metabolic and functional consequences of complete inhibition of creatine kinase by iodoacetamide in the perfused heart].

Treatment of perfused rat hearts with 0.5 mM iodoacetamide (IAAm) for 15 min at different workloads resulting in a nearly complete inhibition of creatine kinase (CK, 99%) was followed by a rapid decline of the phosphocreatine (PCr) level (30%) and a 2-fold increase of the P(i) level which then stabilized. Conversely, the ATP content started to drop monotonously at the beginning of the IAAm washout and reached 30% 90 min after the IAAm removal under medium load. Under low workload the ATP decay occurred at later periods. Neither the ADP-stimulated mitochondrial respiration in skinned fibers, nor the Ca(2+)-stimulated ATPase activity of myofibrils was affected by IAAm treatment. The sensitivity of the resting tension of skinned fibers to Ca2+ tended to a slight increase. The cardiac work index (PRP-pressure-rate product) decreased by 25%, while the end diastolic pressure (EDP) rose by 15 mm Hg when IAAm acted under medium load. In contrast, under low work these parameters were practically stable. The hearts poisoned with IAAm performed a two times lower maximal work and had reduced (by 35%) oxygen consumption rates. The efficiency of energy utilization for mechanical work decreased by 40%. The changes in PRP and EDP correlated with the cytosolic [ATP]/[ADP] ratio in such a way that the decrease in the latter was associated with a decrease in PRP and the elevation of EDP. These data suggest that the creatine kinase system is necessary for the effective translation of a high [ATP]/[ADP] ratio from the intermembrane space of mitochondria to the cytoplasm, myofibrils and ionic pumps. This provides a high level of mechanical work and good relaxation of the left ventricle and protects cytosolic adenine nucleotides from the breakdown.

Adenine Nucleotides↗
PubMed1992

[Functional significance of 2 pathways of energy transport in cardiomyocytes].

To study the relative roles of creatine kinase (CK) and adenylate systems in cardiac energy turnover, the effect of CK inhibitor, iodoacetamide- (IAA, 0.5 mM), and 2-deoxyglucose-(DOG, 2 mM) induced) 65% depletion of adenine nucleotides at slightly decreased CK flux was determined in isolated rat heart. Both substances did not substantially affect contractile parameters of the isovolumic heart. However, an augmentation of cardiac work induced by isoproterenol addition was feeble and transient in IAA-treated hearts while the response of DOG-treated hearts was well preserved. The cardiac failure after IAA treatment was associated with irreversible fall in myocardial ATP content as evidenced by 31P-NMR technique. Furthermore, these hearts were unable to perform cardiac pump function due to insufficient cardiac filling and distensibility. The DOG-treated hearts exhibited 50% reduction in the pump function and were able to increase their work in elevated resistance. The results suggest that CK pathway is extremely important for both full cardiac relaxation and maximal contractile function.

Adenosine Triphosphate↗
PubMed1992

[Cellular mechanisms of impaired cardiac energetics in patients with dilated cardiomyopathy: decrease in mitochondrial respiration and creatine kinase expression].

The mitochondrial functional characteristics were assessed in the biopsy specimens from patients with various Functional Classes dilated cardiomyopathy (DCMP). The assessment was made by using endomyocardial biopsy specimens weighing 2-4 mg which had been taken from 39 patients aged 19-64 years during coronary ventriculography and cardiac transplantation. The status of mitochondria and the efficiency of mitochondrial creatine kinase functioning were evaluated by recording the respiration of saponin-skinned muscular fibers. The maximum mitochondrial respiration rate calculated on a dry weight basis was not substantially different in all functional classes of DCMP, while the acceptor control index (Vmax/V0) and the level of creatine-activated respiration decreased with an increase in the functional class of DCMP. The findings show a good positive correlation between ejection fraction and creatine-stimulated respiration values and a linear negative correlation between this parameter and end-diastolic pressures. Thus, the respiratory parameters of mitochondria in the endomyocardial biopsy specimens may be used to assess the severity of cardias lesions.

Adult↗
PubMed1991

In vivo regulation of mitochondrial respiration in cardiomyocytes: specific restrictions for intracellular diffusion of ADP.

Relative diffusivities of ADP and creatine in cardiomyocytes were studied. The isolated rat cardiomyocytes were lysed with saponin (40 micrograms/ml) to perforate or completely disrupt sarcolemma that was evidenced by leakage of 80-100% lactate dehydrogenase. In these cardiomyocytes mitochondria were used as 'enzymatic probes' to determine the average local concentration of substrates exerting acceptor control of respiration--ADP or creatine (the latter activates respiration via mitochondrial creatine kinase reaction)--when their concentrations in the surrounding medium were changed. The kinetic parameters for ADP and creatine in control of respiration of saponin-treated cardiomyocytes were compared with those determined in isolated mitochondria and skinned cardiac fibers. The apparent Km for creatine (at 0.2 mM ATP) was very close and in a range of 6.0-6.9 mM in all systems studied, showing the absence of diffusion difficulties for this substrate. On the contrary, the apparent Km for ADP increased from 18 +/- 1 microM for isolated mitochondria to 250 +/- 59 microM for cardiomyocytes with the lysed sarcolemma and to 264 +/- 57 microM for skinned fibers. This elevation of Km was not eliminated by inhibition of myokinase with diadenosine pentaphosphate. When 25 mM creatine was present, the apparent Km for ADP decreased to 36 +/- 6 microM. These data are taken to indicate specific restrictions of diffusion of ADP most probably due to its interaction with intermediate binding sites in cardiomyocytes. The important role of phosphocreatine-creatine kinase system of energy transport is to overcome the restrictions in regulation of energy fluxes due to decreased diffusivity of ADP.

Adenosine Diphosphate↗
PubMed1991

Intracellular alterations of the creatine kinase isoforms in brains of schizophrenic patients.

Postmortem brain tissues of schizophrenic patients were found to contain 5-10 times less water-soluble creatine kinase (BB CK) and 1.5-3 times less mitochondrial creatine kinase as compared to control. The major part of BB CK in schizophrenic brain tissues, contrary to control, was found to be insoluble in water (particulate form of BB CK) and could be extracted from brain tissue with strong denaturating agents. The particulate form of BB CK did not have any enzymatic activity but activity was found after the solubilization of this isoenzyme. The observed BB CK translocation into the particulate inactive form and the decrease of mitochondrial CK content to schizophrenic brains may reflect changes in the synthesis and the utilization of creatine phosphate.

Brain↗
PubMed1991

Improvement in contractile recovery of isolated rat heart after cardioplegic ischaemic arrest with endogenous phosphocreatine: involvement of antiperoxidative effect?

STUDY OBJECTIVE: The aim was to attempt to get further insight into the mechanism of the cardioprotective action of phosphocreatine (PCr). DESIGN: Three experimental protocols were used: (1) The effect was examined of exogenous PCr (10 mmol.litre-1) on myocardial oxidative damage produced by H2O2 perfusion (90 mumol.litre-1) of isolated rat heart. (2) Isolated rat hearts were subjected to 35 min cardioplegic ischaemia followed by reperfusion. A control group was studied along with two PCr groups, one corrected for Ca2+ to compensate its binding with PCr (1.4 mmol.litre-1 CaCl2 in St Thomas's Hospital cardioplegic solution), and the other not (1.2 mmol.litre-1). (3) The effect was studied of PCr alone and in combination with the antioxidant tocopherol phosphate (0.1 mumol.litre-1) on contractile and metabolic recovery of isolated rat heart reperfused after 40 min cardioplegic ischaemia. EXPERIMENTAL MATERIAL: Studies were performed on hearts of 84 male Wistar rats, weighing 250-300 g. MEASUREMENTS AND MAIN RESULTS: (1) Oxidative stress resulted in irreversible contracture and impairment of sarcolemmal integrity revealed by using the transmembrane tracer ionic lanthanum. These effects coincided with the decrease of developed pressure from 116 (SEM 3) to 38(3) mm Hg and rate-pressure product from 498(13) to 165(16) mm Hg.s-1. The Ca2+ binding property of PCr was estimated experimentally and the stability constant of the complex CaPCr was found to be 35.4(0.7) mmol; from this the Ca2+ bound by PCr was calculated to be 14% in the experimental conditions used. Ca2+ concentration in K-H buffer containing PCr was increased to compensate its binding with PCr. PCr prevented H2O2 induced contracture, preserved sarcolemmal integrity, and attenuated H2O2 induced decrease in developed pressure and rate-pressure product [73(6) mm Hg and 340(28) mm H.s-1, respectively, p less than 0.05 compared with control]. (2) PCr reduced the diastolic pressure [29(10) v 68(10) mm Hg in control group at 30 min of reperfusion, p less than 0.05] and enhanced the developed pressure [81(10) v 46(10) mm Hg in controls, p less than 0.05] and rate-pressure product [325(44) v 158(40) mm Hg.s-1 in controls, p less than 0.05]. When CaCl2 was increased to 1.4 mmol.litre-1 the protective effect of PCr was not abolished. (3) PCr resulted in improvement of developed pressure [49(7) v 18(5) mm Hg in controls at 40 min of reperfusion, p less than 0.05] and rate-pressure product [184(27) v 71(20) mm Hg.s-1 in controls, p less than 0.05]. The degree of contractile recovery in the tocopherol group was almost the same as in the PCr group. Combined addition of PCr and tocopherol further increased the developed pressure and rate-pressure product to 72(4) mm Hg and 284(23) mm Hg.s-1, respectively. Similarly, PCr and tocopherol in combination provided substantial inhibition of creatine kinase release into perfusate, at 3.8(0.4) v 10.9(2.5) IU in controls, p less than 0.05. CONCLUSIONS: PCr decreases the vulnerability of myocardium to oxidative stress and ischaemic damage. These effects cannot be explained by PCr induced shifts in Ca2+ concentration. Protective effects of PCr and tocopherol are quantitatively additive, most probably due to their different mechanisms of action, and tocopherol may be effective in extending the ability of PCr to stabilise cell membrane structure.

Animals↗
PubMed1991

Phosphocreatine pathway for energy transport: ADP diffusion and cardiomyopathy.

Chemically skinned (by treatment with saponin, 40 micrograms/ml) isolated cardiomyocytes were used to study the intracellular diffusion of ADP and creatine (Cr). Stimulation of respiration was studied in these cardiomyocytes without intact sarcolemma and in isolated heart mitochondrial by addition of ADP and Cr in the presence of 0.2 mM ATP (via mitochondrial creatine kinase reaction: Cr + MgATP = MgADP + PCr). The Michaelis constant (Km) for Cr was similar in both cases, 5.67 +/- 0.11 (SD) mM in skinned myocytes and 6.9 +/- 0.2 mM in mitochondria, showing that there is no significant restriction to the diffusion of this substrate. However, the apparent Km for external ADP increased from 17.6 +/- 1.0 microM for mitochondria to 250 +/- 38 microM for skinned cardiomyocytes, showing decreased diffusivity of ADP as a result of binding to cellular structures. In the presence of 25 mM Cr, the Km for ADP for myocytes decreased to 35.6 +/- 5.6 microM due to the coupling of the creatine kinase and oxidative phosphorylation reactions. Provision of substrate for the creatine kinase reaction amplified the weak ADP signal in the regulation of respiration. The activity of the mitochondrial creatine kinase was decreased by a factor of two in cardiomyopathic hamsters and human hearts and was associated with a twofold decrease in creatine-stimulated respiration. These data show a potentially key role of mitochondrial creatine kinase in the regulation of cellular respiration and the possible importance of changes in its activity for the functional disturbances of the cardiomyopathic heart.

Adenosine Diphosphate↗
PubMed1991

Control of cardiac energy turnover by cytoplasmic phosphates: 31P-NMR study.

Energy flux, estimated from the cardiac work index (pressure-rate product) and the rate of oxygen consumption, was varied in different ways; and the free concentrations of cytosolic phosphates were detected by the 31P-nuclear magnetic resonance method. A reversible decrease in phosphocreatine (PCr) and concomitant increase in [ADP] at nearly constant Pi were induced by 2-deoxyglucose (2-DG) treatment and its subsequent washout and were followed by a reversible suppression of pressure-rate product and elevation of end-diastolic pressure. 2-DG treatment also resulted in an irreversible and severe reduction of the cytosolic adenine nucleotide pool (to approximately one-third of control value) that did not recover during 2-DG washout. Reduction of the energy turnover rate, either by suppression of the PCr shuttle with iodoacetamide or by inhibition of the respiratory chain with amytal, was associated with a drop of PCr level, an elevation of both [ADP] and [Pi], and a rise of end-diastolic pressure. In contrast, a decrease in energy flux by reduction of perfusate Ca2+ led to a PCr rise and a fall in [ADP] and [Pi]. Most of these experimental groups were exposed to two types of loads, isoproterenol stimulation and coronary flow (CF) elevation. Iodoacetamide-treated hearts showed a poor mechanical response to both types of loads compared with other groups. The metabolic response to isoproterenol was uniform in all groups and was associated with some decrease in PCr and increase of [ADP] and [Pi], implying limitations in the respiratory chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1991

Thyroid control over membrane processes in rat heart.

We have studied the effects of hypo- and hyperthyroidism on sarcolemmal (SL) and sarcoplasmic reticular (SR) ion transport processes and mitochondrial energy production in rat heart. The following conclusions were derived. 1) Compared with euthyroid state, hyperthyroidism led to increased SR Ca(2+)-accumulation. In SL, the activities of Ca(2+)-stimulated adenosine triphosphatase (ATPase), ATP-dependent Ca2+ pumping, and Na(+)-Ca2+ exchanger were not affected; but ouabain-sensitive Na(+)-K(+)-ATPase activity was enhanced. 2) Hypothyroidism resulted in depressed activities of Ca2+ pumps both in SL and SR. In SL, the Na(+)-K(+)-ATPase activity was decreased, but Na(+)-Ca2+ exchange was unaltered. 3) Thus slower relaxation of the hypothyroid myocardium may be attributed to depressed functioning of Ca2+ pumps in SR and SL, whereas faster relaxation of the hyperthyroid heart may be based on increased Ca(2+)-pumping activity of SR. 4) Hyperthyroidism and hypothyroidism, respectively, led to enhanced and decreased rates of mitochondrial phosphocreatine synthesis. The thyroid state appears to control the functional coupling between mitochondrial creatine kinase and ATP-ADP translocase: the energy of oxidative phosphorylation was transformed into phosphocreatine more effectively in mitochondria from hypothyroid hearts than in those from hyperthyroid hearts.

Adenosine Triphosphatases↗
PubMed1991

[Membranotropic effect of phosphocreatine and its structural analogs].

The effects of phosphocreatine (PCr) and its analogues (creatine, phosphocreatinine, phosphoarginine and inorganic phosphate) on liposomal and erythrocyte membranes and on the sarcolemmal membrane of cardiomyocytes were studied. The ESR spectrum of the spin-labeled probe, 5-doxyl-stearate, incorporated into the membrane were recorded for analysis of the structural order of the phospholipid bilayer of these membranes. PCr and its analogues had no effect on the structure of the phospholipid bilayer in liposomes; this effect was temperature-independent. However, in erythrocyte and sarcolemmal membranes the rigidity of the membranes was increased by these compounds (except for creatine) at temperatures above 38-40 degrees C. Analysis of these and literary data revealed that cardiac cell membranes may be the site of protective action of PCr on the ischemic myocardium. The lack of effect on liposomes may suggest that the membrane-stabilizing effect of PCr depends on the presence of membrane proteins. The compounds under study may influence the lipid-protein interactions by increasing the rigidity of membrane phospholipids. These membranotropic effects may be due to the interaction of charged molecules of the compounds with polar heads of phospholipids and/or polar groups of proteins in the membrane interphase which, in turn, may influence the packing of hydrophobic fatty acid chains.

Animals↗
PubMed1991

[Phosphocreatine, tocopheryl phosphate and their combination in acute ischemia and myocardial reperfusion in dogs: the effect on rhythm disorders, left ventricle contractility and infarct size].

The effects of phosphocreatine and tocopheryl phosphate and their combined use in ischemia and reperfusion of the heart were studied in anesthetized dogs. The investigation focused on the size of myocardial infarction and left ventricular contractility, ischemic and reperfusion arrhythmias were assessed using Holter monitoring. Phosphocreatine was found to reduce the number of arrhythmias and to prevent the fatal outcomes in myocardial ischemia animals but not to influence the reperfusion rhythm disturbances. Combined administration of tocopheryl phosphate and phosphocreatine, in contrast to their isolated use, completely prevented the development of ventricular fibrillations and fatal outcomes in the animals with reconstructed coronary flow. Administration of phosphocreatine restricted the infarction size, combined use of the drugs facilitated its further reduction, while the group with isolated administration of tocopheryl phosphate showed the infarction size to differ insignificantly from the control values. Combined administration of the drugs, unlike their use alone, improved left ventricular contractility in reperfusion of ischemic myocardium. The cardioprotective effect observed in combined administration of the drugs was attended with depressed lipid peroxidation in reperfused myocardium.

Animals↗
PubMed1990

Combination of 31P-NMR magnetization transfer and radioisotope exchange methods for assessment of an enzyme reaction mechanism: rate-determining steps of the creatine kinase reaction.

The theoretical analysis of a reversible enzyme reaction performed in this work shows that the 31P-NMR magnetization (saturation) transfer technique combined with a radioisotope exchange method may potentially provide information on the position of rate-determining step(s). It depends on chemical shifts of NMR signals of nuclei of interest in free and enzyme-bound forms of substrate(s) and product(s) of the reaction. The creatine kinase reaction (MgATP + creatine----MgADP + P-creatine) has been used as a model. Chemical shifts of 31P in binary, ternary and transitional state substrate-enzyme complexes have been estimated by the variable frequency saturation transfer (VFST) method. This method is based on selective irradiation of numerous points in the spectrum and observation of changes in the intensity of visible line(s) which occur due to chemical exchange between it and lines which are not visible in the routine spectrum. Also, dissociation rate constants of MgADP-containing complexes were determined. Magnetization exchange rates, P-creatine----[gamma-P]MgATP and [beta-P]MgADP----[beta-P]MgATP, were compared with radioisotope exchange rates, [gamma-32P-MgATP----P-creatine and [3H]MgADP----MgATP at different [P-creatine]/[creatine] ratios and at different temperatures. All these exchange rates were close to each other at 30-37 degrees C and [PCr]/[Cr] ratios lower than 2. It is concluded that phosphoryl group transfer is the rate-determining step of the overall creatine kinase reaction under these conditions. However, at lower temperatures (below 25 degrees C) or at high [PCr]/[Cr] ratios ([ADP] less than 20 microM) the rate-determining step seems to be shifted toward dissociation of nucleotide substrates from enzyme-substrate complexes, since exchange rates became significantly different. This approach is useful for analysis of mechanism of enzymatic reactions and also can be applied to non-enzymatic reactions and evaluation of small rapidly exchangeable metabolite pools.

Adenosine Diphosphate↗