Kinetics simulation of transmembrane transport of ions and molecules through a semipermeable membrane.

We have developed a model to study the kinetics of the redistribution of ions and molecules through a semipermeable membrane in complex mixtures of substances penetrating and nonpenetrating through a membrane. It takes into account the degree of dissociation of these substances, their initial concentrations in solutions separated by a membrane, and volumes of these solutions. The model is based on the assumption that only uncharged particles (molecules or ion pairs) diffuse through a membrane (and not ions as in the Donnan model). The developed model makes it possible to calculate the temporal dependencies of concentrations for all processing ions and molecules at system transition from the initial state to equilibrium. Under equilibrium conditions, the ratio of ion concentrations in solutions separated by a membrane obeys the Donnan distribution. The Donnan effect is the result of three factors: equality of equilibrium concentrations of penetrating molecules on each side of a membrane, dissociation of molecules into ions, and Le Chatelier's principle. It is shown that the Donnan distribution (irregularity of ion distribution) and accordingly absolute value of the Donnan membrane potential increases if: (i) the nonpenetrating salt concentration (in one of the solutions) and its dissociation constant increases, (ii) the total penetrating salt concentration and its dissociation constant decreases, and (iii) the volumes ratio increases (between solutions with and without a nonpenetrating substance). It is shown also that only a slight difference between the degrees of dissociation of two substances can be used for their membrane separation.

[Magnetic Magnesium Isotope Accelerates ATP Hydrolysis Catalyzed by Myosin].

In this paper, we present the results of experimental studies on the influence of different magnesium isotopes, the magnetic 25Mg and nonmagnetic 24Mg and 26Mg on ATP activity of the isolated myosin subfragment-1. The reaction rate in the presence of magetic 25Mg isotope turned out to be 2.0-2.5 times higher than that using nonmagnetic 24Mg and 2 Mg isotopes. No magnetic isotope effect was observed in the absence of the enzyme as in spontaneous ATP hydrolysis in aqueous solution. Hence, a significant catalytic effect of the magnetic 25Mg isotope (nuclear spin catalysis) was observed in the enzymatic hydrolysis of ATP.

Ca(2+)-dependent regulation of the Ca(2+) concentration in the myometrium mitochondria. I. Trifluoperazine effects on mitochondria membranes polarization and [Ca(2+)](m).

Са2+-dependent regulation of Ca2+ exchange in mitochondria is carried out with participation of calmodulin. We have shown previously that calmodulin antagonists reduced the level of mitochondrial membrane polarization and induced increase of the ionized Са concentration in both the mitochondrial matrix and cell cytoplasm. The concentration-dependent influence of trifluoperazine on the level of polarization of mitochondrial membranes has been shown in this work. The coordinates of the Hill graphs were used to calculate the constant K0.5 and the Hill coefficient. K0.5 was 24.4 ± 5 µM (n = 10). The Hill coefficient was 2.0 ± 0.2, indicating the presence of two centers of the trifluoperazine binding. We have also studied [Ca2+]m changes, when incubating mitochondria in mediums of different composition: without ATP and ions of Mg (0-medium), in the presence of 3 mM Mg (Mg-medium) and 3 mM Mg + 3 mM ATP (Mg,ATP-medium). It was shown that the composition of the incubation medium affected the [Ca2+]m values in the absence of exogenous Ca2+ and did not affect them in the presence of the latter. Preincubation of mitochondria in mediums of different composition with 25 µM trifluoperazine did not affect the [Ca2+]m values both before and after the addition of 100 µÐœ Са2+ to the incubation medium. It was concluded, that trifluoperazine depolarized myometrial mitochondria membranes in concentration-dependent manner. However, mitochondria preincubation with 25 µM trifluope­razine accompanied by 50% decrease in membrane polarization did not affect the [Ca2+]m values.

Calix[4]arene C-90 and its analogs activate ATPase of the myometrium myosin subfragment-1.

Numerous female reproductive abnormalities are consequences of disorders in uterus smooth muscle (myometrium) contractile function. In this work, we described activators of ATPase, which could be used for development of effective treatments for correcting this dysfunction. Myosin ATPase localized in the catalytic domain of myosin subfragment-1 transforms a chemical energy deposited in macroergic bonds of ATP into mechanical movement. It was shown that сalix[4]arene C-90 and its structural analogs functionalized at the upper rim of macrocycle with four or at least two N-phenylsulfonуltrifluoroacetamidine groups, are able to activate ATP hydrolysis catalyzed by myometrium myosin subfragment-1. It was shown with the method of computer modeling that N-phenylsulfonуltrifluoroacetamidine groups of calix[4]arene C-90 interact with responsible for binding, coordination and the hydrolysis of ATP amino acid residues of myosin subfragment-1. The results can be used for further research aimed at using calix[4]arene C-90 and its analogs as pharmacological compounds that can effectively normalize myometrium contractile hypofunction.

[Mg2+,ATP-DEPENDENT PLASMA MEMBRANE CALCIUM PUMP OF SMOOTH MUSCLE CELLS. II. REGULATION OF ACTIVITY].

Plasma membrane Ca2+-pump is one of key proteins, which takes part in Ca2+ exchange in smooth muscle cells. It has a lot of diverse functions from control of basal cytoplasmal Ca2+ concentration to regulation of proteins involved in Ca2+-dependent signal pathway. Ca2+ pump function is often dependent on the isoform or even form of alternative splicing. Allowing for a variety of Ca2+-pump functions and properties, which were reviewed in detail in the first part of our review article cycle (Ukr. Biochem. J, 2015; 87(1)), the precise control of the mentioned pump activity is very important for cell functioning. The other part of this article is dedicated to different regulation factors of smooth muscle plasma membrane Ca2+-pump activity: endogenous and exogenous, biotic and abiotic factors. Special attention is given to literature data and own results about design and the search of selective plasma membrane Ca2+-pump inhibitor which would allow examining its functioning in smooth muscle cells more meticulously.

[Mg2+, ATP-dependent plasma membrane calcium pump of smooth muscle cells. I. Structural organization and properties].

Tight control of cytoplasm Ca2+ concentration is essential in cell functioning. Changing of Ca2+ concentration is thorough in smooth muscle cells, because it determines relaxation/constraint process. One of key proteins which control Ca2+ concentration in cytoplasm is Mg2+, ATP-dependent plasma membrane calcium pump. Thus, it is important to find compoumds which allowed one to change Mg2+, ATP-dependent plasma membrane calcium pump activity, as long as this topic is of current interest in biochemical research which regards energy and pharmacomechanical coupling mechanism of muscle excitation and contraction. In this article we generalized literatute and own data about properties of smooth muscle cell plasma membrane Ca(2+)-pump. Stuctural oganization, kinetical properties and molecular biology are considered.

ELECTROCHEMICAL POTENTIAL OF THE INNER MITOCHONDRIAL MEMBRANE AND Ca2+ HOMEOSTASIS OF MYOMETRIUM CELLS.

We demonstrated using Ca(2+)-sensitive fluorescent probe, mitochondria binding dyes, and confocal laser scanning microscopy, that elimination of electrochemical potential of uterus myocytes' inner mitochondrial membrane by aprotonophore carbonyl cyanide m-chlorophenyl hydrazone (10 µM), and by a respiratory chain complex IV inhibitor sodium azide (1 mM) is associated with substantial increase of Ca2+ concentration in myoplasm in the case of the protonophore effect only, but not in the case of the azide effect. In particular, with the use of nonyl acridine orange, a mitochondria-specific dye, and 9-aminoacridine, an agent that binds to membrane compartments in the presence of proton gradient, we showed that both the protonophore and the respiratory chain inhibitor cause the proton gradient on mitochondrial inner membrane to dissipate when introduced into incubation medium. We also proved with the help of 3,3'-dihexyloxacarbocyanine, a potential-sensitive carbocyanine-derived fluorescent probe, that the application of these substances results in dissipation of the membrane's electrical potential. The elimination of mitochondrial electrochemical potential by carbonyl cyanide m-chlorophenyl hydrazone causes substantial increase in fluorescence of Ca(2+)-sensitive Fluo-4 AM dye in myoplasm of smooth muscle cells. The results obtained were qualitatively confirmed with flow cytometry of mitochondria isolated through differential centrifugation and loaded with Fluo-4 AM. Particularly, Ca2+ matrix influx induced by addition of the exogenous cation is totally inhibited by carbonyl cyanide m-chlorophenyl hydrazone. Therefore, using two independent fluorometric methods, namely confocal laser scanning microscopy and flow cytometry, with Ca(2+)-sensitive Fluo-4 AM fluorescent probe, we proved on the models of freshly isolated myocytes and uterus smooth muscle mitochondria isolated by differential centrifugation sedimentation that the electrochemical gradient of inner membrane is an important component of mechanisms that regulate Ca2+ homeostasis in myometrium cells.

CALMODULIN ANTAGONISTS EFFECT ON Ca2+ LEVEL IN THE MITOCHONDRIA AND CYTOPLASM OF MYOMETRIUM CELLS.

It is known that Ca(2+)-dependent regulation of this cation exchange in mitochondria is carried out with participation of calmodulin. We had shown in a previous work using two experimental models: isolated mitochondria and intact myometrium cells, that calmodulin antagonists reduce the level of mitochondrial membrane polarization. The aim of this work was to investigate the influence of calmodulin antagonists on the level of ionized Ca in mitochondria and cytoplasm of uterine smooth muscle cells using spectrofluorometry and confocal microscopy. It was shown that myometrium mitochondria, in the presence of ATP and MgCl2 in the incubation medium, accumulate Ca ions in the matrix. Incubation of mitochondria in the presence of CCCP inhibited cation accumulation, but did not cease it. Calmodulin antagonist such as trifluoperazine (100 µm) considerably increased the level of ionized Ca in the mitochondrial matrix. Preliminary incubation of mitochondria with 100 µM Ca2+, before adding trifluoperazine to the incubation medium, partly prevented influence of the latter on the cation level in the matrix. Incubation of myometrium cells (primary culture) with another calmodulin antagonist calmidazolium (10 µM was accompanied by depolarization of mitochondrial membrane and an increase in the concentration of ionized Ca in cytoplasm. Thus, using two models, namely, isolated mitochondria and intact myometrium cells, it has been shown that calmodulin antagonists cause depolarization of mitochondrial membranes and an increase of the ionized Ca concentration in both the mitochondrial matrix and the cell cytoplasm.

CALIX[4]ARENE C-99 INHIBITS MYOSIN ATPase ACTIVITY AND CHANGES THE ORGANIZATION OF CONTRACTILE FILAMENTS OF MYOMETRIUM.

Calix[4]arenes are cup-like macrocyclic (polyphenolic) compounds, they are regarded as promising molecular "platforms" for the design of new physiologically active compounds. We have earlier found that calix[4]arene C-99 inhibits the ATPase activity of actomyosin and myosin subfragment-1 of pig uterus in vitro. The aim of this study was to investigate the interaction of calix[4]arene C-99 with myosin from rat uterine myocytes. It was found that the ATPase activity of myosin prepared from pre-incubated with 100 mM of calix[4]arene C-99 myocytes was almost 50% lower than in control. Additionally, we have revealed the effect of calix[4]arene C-99 on the subcellular distribution of actin and myosin in uterus myocytes by the method of confocal microscopy. This effect can be caused by reorganization of the structure of the contractile smooth muscle cell proteins due to their interaction with calix[4]arene. The obtained results demonstrate the ability of calix[4]arene C-99 to penetrate into the uterus muscle cells and affect not only the myosin ATPase activity, but also the structure of the actin and myosin filaments in the myometrial cells. Demonstrated ability of calix[4]arene C-99 can be used for development of new pharmacological agents for efficient normalization of myometrial contractile hyperfunction.

[Ca2+/H(+)-exchange in myometrium mitochondria].

Using the fluorescent probe Fluo-4 AM the authors have identified Na(+)-independent Ca2+H(+)-exchange in isolated mitochondria of rat myometrium and studied its individual properties. Formation of directional protons gradient in the matrix of mitochondria causes antyporte release of Ca2+, which has been previously accumulated in energetic processes (in the presence of Mg-ATP and succinate). The functioning of Ca2+/H(+)-exchange depends on the proton gradient and is characterized by reversibility, in case of extramitochondria environment alkalization the additional accumulation of Ca2+ by organelles is recorded. Monovalent cations gradients (Na+, K+, Li+) do not cause the release of Ca2+ from mitochondria. Rate of Ca2+/H(+)-exchange is growing in terms of increasing deltapH on the mitochondria membrane and kinetics of deltapH-induced Ca2+ release from the matrix corresponds to the laws of first order reaction. Research of Ca2+/H(+)-exchange some properties in the myometrium mitochondria showed that the above transport process is of electrogenic nature, perhaps it is done in a 1: 1 stechiometry (Hill coefficient on H+ close to 1) and is able to adjust matrix Ca2+ concentration under physiological conditions (pH activation of about 6.9). Thus, in the inner membrane of the myometrium mitochondria the available system of the secondary active Ca(2+)-transport from the matrix of these organelles to myoplasm and the functioning of Ca2+/H(+)-exchanger may underlie this process.

[Nitric oxide as a possible regulator of energy-dependent Ca2+ transport in mitochondria of uterine smooth muscle].

The influence of the donor and the precursor of NO, namely 100 mM sodium nitroprusside and sodium nitrite on the energo-dependent Ca(2+)-transport in isolated mitochondria from rat myometrium was investigated. Changes in the mitochondrial matrix Ca(2+)-concentration was evaluated by spectrofluorimetry using Ca2+ sensitive probe Fluo-4 AM. Mg(2+)-ATP-dependent Ca(2+)-accumulation on mitochondria in the presence of succinate significantly stimulated by nitric oxide, in particular, 100 microM sodium nitroprusside amplified the transport by 1.6 times relative to its control values. NO effect becomes significant only when the incubation of mitochondria with the compounds was performed. Ca(2+)-accumulation in the presence of sodium nitroprusside effectively suppressed by protonophore (CCCP) and ruthenium red (10 microM). It was concluded that inner mitochondrial membrane Ca(2+)-uniporter stimulated by nitrogen oxide. Ca(2+)-accumulation in mitochondria in the presence of sodium nitroprusside was not sensitive to the action of a specific permeability transition pore inhibitor cyclosporine (5 microM). This data indicates that the role of permeability transition pore is less significant than Ca(2+)-uniporter in the processes of Ca(2+)-transport in mitochondria under the nitric oxide action. Thus, nitric oxide stimulates the energo-dependent Ca(2+)-accumulation by myometrium mitochondria mediated their inner membrane Ca(2+)-uniporter functioning.

[Modulation of myometrium mitochondrial membrane potential by calmodulin antagonists].

Influence of calmodulin antagonists on mitochondrial membrane potential was investigated using a flow cytometry method, confocal microscopy and fluorescent potential-sensitive probes TMRM and MTG. Influence of different concentrations of calmodulin antagonists on mitochondrial membrane potential was studied using flow cytometry method and a fraction of myometrium mitochondria of unpregnant rats. It was shown that 1-10 microM calmidazolium gradually reduced mitochondria membrane potential. At the same time 10-100 microM trifluoperazine influenced as follows: 10 microM--increased polarization, while 100 microM--caused almost complete depolarization of mitochondrial membranes. In experiments which were conducted with the use of confocal microscopy method and myometrium cells it was shown, that MTG addition to the incubation medium led to the appearance of fluorescence signal in a green range. Addition of the second probe (TMRM) resulted in the appearance of fluorescent signal in a red range. Mitochondrial membrane depolarization by 1 microM CCCP or 10 mM NaN3 was accompanied by the decline of "red" fluorescence intensity, "green" fluorescence was kept. The 10-15 minute incubation of myometrium cells in the presence 10 microM calmidazolium or 100 microM trifluoperazine was accompanied by almost complete decrease of the TMRM fluorescent signal. Thus, with the use of potential-sensitive fluorescent probes TMRM and MTG it was shown, that calmodulin antagonists modulate mitochondrial membrane potential of myometrium cells.

[Investigation of nitrosactive compounds influence on polarization of the mitochondrial inner membrane in the rat uterus myocytes using potential sensitive fluorescent probe DiOC6(3)].

The effect of nitrosactive compounds (sodium nitroprusside and sodium nitrite) on the polarization level of the uterus myocytes inner mitochondrial membrane using the confocal laser microscopy and fluorescent probe potentialsensitive DiOC6(3) (3,3'-dihexyloxacarbocyanine) was ivestigated. Colocalisation of mitochondrial membranes specific fluorescent probes (MitoTracker Orange CM-H2TMRos, 10 - nonyl acridine orange and DiOC6(3)) was demonstrated. It was shown that sodium nitroprusside at 0.1 mM concentration caused a moderate decrease in mitochondrial transmembrane potential. That observation was confirmed by flow cytometry. Action efficiency of sodium nitrite in a similar concentration was significantly lower than that of sodium nitroprusside. It is shown that it was sodium nitroprusside which caused a slight swelling of the mitochondria. A possible protecting role of nitric oxide as to mitochondria was discussed.

[Kinetics of inhibitory effect of calix[4]arene C-90 on activity of transporting plasma membrane Ca2+, Mg2+-ATPase of smooth muscle cells].

In experiments on the suspension of myometrium cell plasma membrane, processed by 0.1% digitonin, the inhibitory action of calix[4]arene C-90 (5,11,17,23-tetra(threeftor)methyl(phenilsulphonilimino)-methylamino-25,26,27,28-tetrapropoxy-calix[4]arene) on the activity of Ca2+,Mg2+-ATPase was investigated. The authors also examined the influence of calix[4]arene in different concentration on affinity of enzyme (Ca2,Mg2+-ATPase) for the ATP and ions of Mg and Ca, and its influence on cooperative effect and maximum velocity of ATP hydrolysis. It is shown that calix[4]arene does not influence the affinity of Ca2+,Mg2+-ATPase for the ATP, which means that these two compounds have different binding centers. Also calix[4]arene has no influence on affinity and cooperative effect of Ca ions, if it is used in concentration lower than 50 µM. Calix[4]arene slightly increases coefficient of Ca2+,Mg2+-ATPase activation by magnesium chloride. In all three cases, where ATP, Mg and Ca ions are used to test the impact of calix[4]arene, maximum velocity of ATP hydrolysis significantly decreases. All these results clarify that calix[4]arene implements its inhibitory action through mechanism of uncompetitive inhibition of Ca2+,Mg2+-ATPase activity.

[Ca ion transport in smooth muscle mitochondria].

Review focuses on the analysis of literature data and own results concerning properties of mitochondria Ca2+ transporting systems and their regulation. Three mechanisms for mitochondrial Ca2+ uptake are described: the electrogenic mitochondrial Ca2+ uniporter, a rapid mode of Ca2+ uptake (RaM) and ryanodine-sensitive Ca2+ channels (RyR). Two mechanisms of Ca2+ efflux from the mitochondrial matrix have been proposed: Na+-dependent and Na+-independent Ca2+ exchange. The mitochondrial permeability transition pore can also function as a Ca2+ efflux mechanism. Ca2+ accumulation in mitochondria resulted in an increase of mitochondrial membrane potential, ATP synthesis and activation of metabolites transport. The dissipation of mitochondrial membrane potential should prevent mitochondrial Ca2+ uptake. Our data concerning depolarizing effect of calmodulin antagonists and hyperpolarizing effect of calix[4]arenes C-136 and C-137 on the myometrium mitochondria can be applied on the demand of mitochondria membrane potential correction.

[Protective effect of tiacalix[4]arene-tetrasulphonate on heavy metal inhibition of myometrium myosin subfragment-1 ATP-hydrolase activity].

Heavy metals have a negative effect on the contractility of uterine smooth muscles (myometrium), these effects can lead to various pathologies of a women reproductive system. To overcome these effects the methods for correcting the myometrium contractile activity are to be developed. Catalyzed by myosin ATPase ATP hydrolysis is the most important reaction in the molecular mechanism of myometrium contraction. We have found an inhibitory effect of 0.03-0.3 mM Ni2+, Pb2+ and Cd2+ on enzymatic hydrolysis of ATP by myosin subfragment-1 obtained from swine uterine smooth muscles. We have demonstrated that 100 µM thiacalix[4]arene-tetrasulphonate (C-798) recovered to the control level of ATPase activity of myosin subfragment-1 in the presence of heavy metal cations. One of the most probable mechanisms of C-798 corrective activity is based on its ability to chelate heavy metals, thus cations Pb, Cd and Ni can be removed from the incubation medium. Computer simulation has demonstrated that the protective effect of C-798 may also be the result of weakening the interaction of heavy metal ions with amino acid residues of the myosin molecule near the active site of ATP hydrolase. The obtained results can be used for further research aimed at assessing the prospects of thiacalix[4]arene-tetrasulfonate as pharmacological compounds.

[Kinetic properties of calixarene C-90 action on the myometrial plasma membrane Ca2+,Mg2+-Atpase activity and on the Ca2+ concentration in unexcited cells of the myometrium].

Plasma membrane Ca2+,Mg2+-ATPase is an important element of general myometrium tonus control mechanism, which also makes a contribution to muscle tension relaxation after its contraction. Expiriments were done on the myometrial cell plasma membrane suspension, which was treated with 0.1% digitonin solution. The authors have investigated the inhibitory action of calix[4]arene C-90 (5,11,17,23-tetra(trifluor) methyl(phenylsulphonylimino)-methylamino-25,26,27,28-tetra propoxi-calix[4]arene) on the Ca2+,Mg2+-ATPase activity (the magnitude of 10.5 was 20.2 +/- 0.5 mkM). The inhibitory action of calix[4]arene C-90 on the activity of Ca2+, Mg2+-ATPase is explained as cooperative action of four trifluormethyl(phenylsulfonylimino)methylamino groups that are spatially oriented on the calix[4]-arene base rather than with the action of tetra-phenol macrocycle or separate pharmacophore sulphonilamidin groups. Considering established kinetic pattern of calix[4]arene C-90 inhibitory action on the plasma membrane Ca2+,Mg2+-ATPase activity, stationary kinetical model of basal calcium concentration control in unexcited uterus myocytes was developed. It is assumed that obtained results may be promising for creation of new generation ("supramolecular") pharmacological agent - uterus basal tonus stimulator - on the base of calix[4] arene C-90.

[Ca2+ accumulation study in isolated smooth muscle mitochondria using fluo-4 AM].

The opportunity of Ca2+-sensitive fluorescent dye Fluo-4 AM and spectrofluorimetry method application for the study of energy-dependent Ca2+ accumulation in mitochondria from uterus smooth muscle is proved. It has been found that the presence of mitochondrial preparation increases time-dependent fluorescent response considerably and this effect depends on Ca2+ concentration in the medium. Thus, in these conditions, deesterification active probe is formed which is sensitive to Ca2+. It is shown that the accumulation of calcium ions in mitochondria in the presence of Mg-ATP and succinate depends on exogenous Ca2+ concentration and is characterized by substrate saturating. The apparent activation constant of Ca2+ accumulation is 53.9 +/- 6.9 mM, which corresponds to the physiological concentration of the cation in the cell next to mitochondria. Transit addition of Ca2+-ionophore A23187 to the incubation me- dium caused a rapid release of ionized cation from mitochondria. When proton gradient on the inner mitochondrial membrane is dissipated by protonophore CCCP, in the case of suppressing the generation of the gradient by oligomycin and in the presence of ruthenium red that inhibits Ca2+ mitochondrial accumulation systems, Ca2+ entry is significantly reduced. The results indicate the prospects of using Fluo-4 AM to study the properties of the Ca2+ accumulation system in isolated mitochondria of the myometrium.

[The calix[4]arene C-107 is highly effective supramolecular inhibitor of the Na+,K(+)-ATPase of plasma membranes].

The inhibition of the Na+,K(+)-ATPase activity of the myometrium cell plasma membranes with calixarene C-107 (5,17-diamino(2-pyridyl) methylphosphono-11,23-di-tret-butyl-26,28-dihydroxy-25,27-dipropoxycalix[4]arene) was investigated. It has been shown that calixarene C-107 reduced the Na+,K(+)-ATPase activity more efficiently than ouabain did, while it did not practically influence the "basal" Mg(2+)-ATPase activity of the same membrane. The magnitude of the cofficient of inhibition I0.5 was 33 +/- 4 nM, Hill coefficient was 0.38 +/- 0.06. The model calixarene C-150--the calixarene "scaffold" (26,28-dihydroxy-25,27-dipropoxycalix[4]arene), and the model compound M-3 (4-hydroxyaniline(2-pyridine)methylphosphonic acid)--a fragment of the calixarene C-107, had practically no influence on the enzymatic activity of Na+,K(+)-ATPase and Mg(2+)-ATPase. We carried out the computer simulation of interaction of calixarenes C-107 and the mentioned model compound with ligand binding sites of the Na+,K(+)-ATPase of plasma membrane and structure foundation of their intermolecular interaction was found out. The participation of hydrogen, hydrophobic, electrostatic and pi-pi (stacking) interaction between calixarene and enzyme aminoacid residues, some of which are located near the active center of Na+,K(+)-ATPase, was discussed.

[Na+, K(+)-ATPase, endogenous cardiotonic steroids and their transducing role].

Na+, K(+)-ATPase--a protein complex of plasmatic membrane, which performs the dual function: firstly, it supports the Na+ and K+ homeostasis, and also transmembrane potential gradient, secondly, it serves as the transducer of signals and as the regulator of the expression of many key genes. Endogenous cardiotonic steroids, which are synthesized in the adrenal glands and hypothalamus, serve as the signal molecules. New concepts about the mechanisms of the realization of the Na+, K(+)-ATPase signal function and their connection with cellular functions, apoptosis, and with pathologies of cardiovascular system and water-salt homeostasis are described in the survey.