Stochastic and deterministic approaches to modelling calcium release in cardiac myocytes at different spatial arrangements of ryanodine receptors.

Calcium release sites (CRSs) play a key role in excitation-contraction coupling of cardiac myocytes. Recent studies based on electron tomography and super-resolution imaging revealed that CRSs are not completely filled with ryanodine receptors (RyRs) and that the spatial arrangement of RyRs is neither uniform nor static. In this work, we studied the effect of spatial arrangement of RyRs on RyR activation using simulations based on Monte Carlo (MC) and mean-field (MF) approaches. Both approaches showed that activation of RyRs is sensitive to the arrangement of RyRs in the CRS. However, the MF simulations did not reproduce results of MC simulations for non-compact CRSs, suggesting that the approximations used in the MF approach are not suitable for simulation studies of RyRs arrangements observed experimentally. MC simulations revealed the importance of realistic spatial arrangement of RyRs for adequate modelling of calcium release in cardiac myocytes.

57Fe Mössbauer study of unusual magnetic structure of multiferroic 3R-AgFeO2.

We report new results of a 57Fe Mössbauer study of hyperfine magnetic interactions in the layered multiferroic 3R-AgFeO2 demonstrating two magnetic phase transitions at T N1 and T N2. The asymptotic value ß * ≈ 0.34 for the critical exponent obtained from the temperature dependence of the hyperfine field H hf(T) at 57Fe the nuclei below T N1 ≈ 14 K indicates that 3R-AgFeO2 shows quasi-3D critical behavior. The spectra just above T N1 (T N1 < T < T * ≈ 41 K) demonstrate a relaxation behavior due to critical spin fluctuations which indicates the occurrence of short-range correlations. At the intermediate temperature range, T N2 < T < T N1, the 57Fe Mössbauer spectra are described in terms of collinear spin-density-waves (SDW) with the inclusion of many high-order harmonics, indicating that the real magnetic structure of the ferrite appears to be more complicated than a pure sinusoidally modulated SDW. Below T < T N2 ≈ 9 K, the hyperfine field H hf reveals a large spatial anisotropy (ΔH anis ≈ 30 kOe) which is related with a local intra-cluster (FeO6) spin-dipole term that implies a conventional contribution of the polarized oxygen ions. We proposed a simple two-parametric formula to describe the dependence of H anis on the distortions of the (FeO6) clusters. Analysis of different mechanisms of spin and hyperfine interactions in 3R-AgFeO2 and its structural analogue CuFeO2 points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.

Different Types of Urinary Steroid Profiling Obtained by High-Performance Liquid Chromatography and Gas Chromatography-Mass Spectrometry in Patients with Adrenocortical Carcinoma.

Urinary steroid profiling (USP) was studied using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) methods in 108 patients with adrenocortical adenoma (ACA) and in 31 patients with adrenocortical carcinoma (ACC). Thirteen ACC and Cushing's syndrome (ACC-CS) patients had two types of USP as well as 18 ACC patients without hypercortisolism. These four types differed by androgen and glucocorticoid secretion of the adrenal cortex. Fifteen main ACC features were observed by GC-MS. Urinary excretion of dehydroepiandrosterone (DHEA) was increased in 67.7 % of ACC patients and tetrahydro-11-deoxycortisol (THS) in 74.2 %. By combination of the following parameters: THS >900 µg/24 h and/or DHEA >1500 µg/24 h with ratios of 3α,16,20-pregnentriol/3ß,16,20-pregnentriol (3α,16,20dP3/3ß,16,20dP3) less than 6.0 and 3α,17,20dP3/3ß,17,20dP3 less than 9.0 and the detection of "non-classical" 5-en-pregnens, not found in ACA and healthy persons, 100 % sensitivity and specificity of ACC and ACA differential diagnosis were achieved. Features of 21-hydroxylase and 11ß-hydroxylase deficiency were observed by GC-MS in 32.2 and 61.3 % of the ACC patients, respectively. Additional features for ACC-CS diagnostic were increased urinary excretion of 6ß-hydroxycortisol, 18-hydroxycorticosterone, the sum (UFF + UFE) obtained by HPLC, tetrahydrocorticosterone, and the sum (THF + THE + allo-THF) obtained by GC-MS.

[ELECTRIC STIMULATION OF VAGUS NERVE MODULATES A PROPAGATION OF OXYGEN EPILEPSY IN RABBITS].

The activation of autonomic afferents (achieved through the vagus nerve (VN) electrical stimulation) on CNS O2 toxicity and cardiovascular function was investigated. In conscious rabbits at 5 ATA 02, prodromal signs of CNS O2 toxicity and convulsion latency were determined with and without vagus nerve (VN) stimulation. EEG, ECG and respiration were also recorded. In rabbits at 5 ATA, sympathetic overdrive and specific patterns on the EEG (synchronization of slow-waves), ECG (tachycardia) and respiration (respiratory minute volume increase) preceded motor convulsions. Vagus nerve stimulation increased parasympathetic component of autonomic drive and significantly delayed prodromal signs of oxygen toxicity and convulsion latency. Autonomic afferent input to the brain is a novel target for preventing CNS toxicity in HBO2.

[Interaction of Membrane and Calcium Oscillators in Cardiac Pacemaker Cells: Mathematical Modeling].

An integrative model of the calcium dynamics in cardiac pacemaker cells is developed taking into account a synergetic effect of the interaction between an outer membrane oscillator and an intracellular calcium oscillator ("membrane and Ca(2+)-clock"). The main feature of the model is a description of the stochastic dynamics of Ca2+ release units within the electron-conformational mechanism of the functioning of ryanodine-sensitive calcium channels. It is shown that interaction of two cellular oscillators provides a stable action potential generation in the cardiac pacemaker cells even in the case of the stochastic Ca2+ dynamics. We studied in detail the effect of ryanodine channels sensitivity to an increase in the intracellular calcium concentration in sarcoplasmic reticulum and in the dyadic space on the behavior of calcium-release system. A parametric analysis of the integrative model of pacemaker cells is performed.

Oxygen tension in rat brain during hyperoxia [corrected].

Critical value of oxygen tension (Po2) and cerebral blood flow in the striatum for seizure appearance during hyperbaric oxygenation (5 ATA) were determined in awake Wistar rats. Seizure activity was observed at Po2=1030±102 mm Hg. A relationship between brain Po2 and blood flow was revealed at different regimens of hyperbaric oxygenation using a mathematical model. Comparison of experimental data and mathematical model showed that seizure-inducing levels of Po2during hyperbaric oxygenation at 4, 5, and 6 ATA can be achieved after increasing blood flow by 1.5-3.0, 1.2-2.0, and 0.8-1.1, respectively.

Perspectives of disproportionation driven superconductivity in strongly correlated 3d compounds.

Disproportionation in 3d compounds can give rise to an unconventional electron-hole Bose liquid with a very rich phase diagram, from a Bose metal, to a charge ordering insulator and an inhomogeneous Bose-superfluid. Optimal conditions for disproportionation driven high-T(c) superconductivity are shown to be realized only for several Jahn-Teller d(n) configurations that permit the formation of well defined local composite bosons. These are the high-spin d(4), low-spin d(7), and d(9) configurations given the octahedral crystal field, and the d(1), high-spin d(6) configurations given the tetrahedral crystal field. The disproportionation reaction has a peculiar 'anti-Jahn-Teller' character lifting the bare orbital degeneracy. Superconductivity in the d(4) and d(6) systems at variance with d(1), d(7), and d(9) systems implies unavoidable coexistence of the spin-triplet composite bosons and the magnetic lattice. We argue that unconventional high-T(c) superconductivity, observed in quasi-2d cuprates with tetragonally distorted CuO(6) octahedra and iron-based layered pnictides/chalcogenides with tetrahedrally coordinated Fe(2+) ions presents a key argument to support the fact that the disproportionation scenario is at work in these compounds.

[Effect of nitric oxide/endothelin interaction on hyperoxic vasoconstruction].

The data obtained demonstrated that NO restrains ET-1 production and blunts ET-1-mediated basal cerebrovascular tone. Local hyperoxygenation of the brain tissue decreases NO availability, supeoxide production, suppresses NO-mediated vascular tone and facilitates ET-1-mediated vasoconstriction.

Autonomic activation links CNS oxygen toxicity to acute cardiogenic pulmonary injury.

Breathing hyperbaric oxygen (HBO2), particularly at pressures above 3 atmospheres absolute, can cause acute pulmonary injury that is more severe if signs of central nervous system toxicity occur. This is consistent with the activation of an autonomic link between the brain and the lung, leading to acute pulmonary oxygen toxicity. This pulmonary damage is characterized by leakage of fluid, protein, and red blood cells into the alveoli, compatible with hydrostatic injury due to pulmonary hypertension, left atrial hypertension, or both. Until now, however, central hemodynamic parameters and autonomic activity have not been studied concurrently in HBO2, so any hypothetical connections between the two have remained untested. Therefore, we performed experiments using rats in which cerebral blood flow, electroencephalographic activity, cardiopulmonary hemodynamics, and autonomic traffic were measured in HBO2 at 5 and 6 atmospheres absolute. In some animals, autonomic pathways were disrupted pharmacologically or surgically. Our findings indicate that pulmonary damage in HBO2 is caused by an abrupt and significant increase in pulmonary vascular pressure, sufficient to produce barotrauma in capillaries. Specifically, extreme HBO2 exposures produce massive sympathetic outflow from the central nervous system that depresses left ventricular function, resulting in acute left atrial and pulmonary hypertension. We attribute these effects on the heart and on the pulmonary vasculature to HBO2-mediated central sympathetic excitation and catecholamine release that disturbs the normal equilibrium between excitatory and inhibitory activity in the autonomic nervous system.

[Mathematical modelling in physiology].

The article illustrates the method of mathematical modelling in physiology as a unique tool to study physiological processes. A number of demonstrated examples appear as a result of long-term experience in mathematical modelling of electrical and mechanical phenomena in the heart muscle. These examples are presented here to show that the modelling provides insight into mechanisms underlying these phenomena and is capable to predict new ones that were previously unknown. While potentialities of the mathematical modelling are analyzed with regard to the myocardium, they are quite universal to deal with any physiological processes.

Involvement of extracellular superoxide dismutase in regulating brain blood flow.

The physiological role of extracellular superoxide dismutase (SOD3) has received insufficient study. We investigated the hypothesis that SOD3, which neutralizes superoxide anions (O2(-)) in the intercellular space of the brain, prevents the inactivation of nitric oxide (NO) and is thus involved in regulating cerebral vascular tone. Local brain blood flow was measured in the striatum of anesthetized rats during administration of various combinations of a SOD mimetic, a SOD inhibitor, an NO donor, and an NOS inhibitor into the striatum using a Hamilton syringe. In normal conditions, SOD3 was found to minimize O2(-) levels, protecting endogenously produced NO at a sufficient level to maintain cerebral vascular tone and reactivity. SOD3 was found to increase the vasodilatory effect of endogenously produced NO in the brain. SOD3 was found to neutralize superoxide anions produced in the brain during respiration of 100% O2 and to maintain basal NO levels and its vasodilatory potential in normobaric hyperoxia.

[Gastrodiscoidosis is a dangerous zoonosis].

The paper gives data on the helminthiasis--gastrodiscoidosis, a zoonotic disease caused by the trematode Gastrodiscoides hominis (Lewis et McConnall, 1876) parasitizing in the animal and human intestine in the endemic foci of both Russia and foreign countries. It also presents information on the morphology of the helminth, the biological cycle of development of the parasite and its habitat and spread, as well as its induced abnormalities and on the method of diagnosing of the disease.

[Involvement of extracellular superoxide dismutase in cerebral blood flow regulation].

Physiological role of extracellular superoxide dismutase (SOD3) remains obscure. We tested the hypothesis that SOD3 regulates the equilibrium between superoxide (O2-) and nitric oxide (NO), thereby controlling vascular tone and cerebrovascular reactivity. In anesthetized rats local blood flow was measured in the striatum after intracerebral delivery of SOD-mimetic, SOD-inhibitor, NO-donor and NOS-inhibitor by microdialysis. We have found that SOD3 minimizes O2- levels preserving NO availability at resting conditions. SOD3 promotes NO mediated vasodilatation by scavenging O2- and basal SOD3 levels is able to inactivate O2- produced by 100% oxygen breathing preserving vasodilator effect of NO.

Activation sequence as a key factor in spatio-temporal optimization of myocardial function.

Using one-dimensional models of myocardial tissue, implemented as chains of virtual ventricular muscle segments that are kinematically connected in series, we studied the role of the excitation sequence in spatio-temporal organization of cardiac function. Each model element was represented by a well-verified mathematical model of cardiac electro-mechanical activity. We found that homogeneous chains, consisting of identical elements, respond to non-simultaneous stimulation by generation of complex spatio-temporal heterogeneities in element deformation. These are accompanied by the establishment of marked gradients in local electro-mechanical properties of the elements (heterogeneity in action potential duration, Ca2+ transient characteristics and sarcoplasmic reticulum Ca2+ loading). In heterogeneous chains, composed of elements simulating fast and slow contracting cardiomyocytes from different transmural layers, we found that only activation sequences where stimulation of the slower elements preceded that of faster ones gave rise to optimization of the system's electro-mechanical function, which was confirmed experimentally. Based on the results obtained, we hypothesize that the sequence of activation of cardiomyocytes in different ventricular layers is one of the key factors of spatio-temporal organization of myocardium. Moreover, activation sequence and regional differences in intrinsic electro-mechanical properties of cardiac muscle must be matched in order to optimize myocardial function.

Electron-conformational model of ryanodine receptor lattice dynamics.

We propose a simple, physically reasonable electron-conformational model for the ryanodine receptor (RyR) and, on that basis, present a theory to describe RyR lattice responses to L-type channel triggering as an induced non-equilibrium phase transition. Each RyR is modelled with a single open and a single closed (electronic) state only, described utilizing a s=12 pseudospin approach. In addition to the fast electronic degree of freedom, the RyR channel is characterized by a slow classical conformational coordinate, Q, which specifies the RyR channel calcium conductance and provides a multimodal continuum of possible RyR states. The cooperativity in the RyR lattice is assumed to be determined by inter-channel conformational coupling. Given a threshold sarcoplasmic reticulum (SR) calcium load, the RyR lattice fires due to a nucleation process with a step-by-step domino-like opening of a fraction of lattice channels, providing for a sufficient release to generate calcium sparks. The optimal mode of RyR lattice functioning during calcium-induced calcium release implies a fractional release with a robust termination due to a decrease in SR calcium load, accompanied by a respective change in effective conformational strain of the lattice. SR calcium overload is shown to result in excitation of RyR lattice auto-oscillations with spontaneous RyR channel opening and closure.

Effect of indomethacin on cerebral blood flow and development of oxygen convulsions.

Hyperbaric oxygenation modulates cerebral blood flow affecting the development of oxygen convulsions. Before hyperbaric oxygenation-induced convulsions in rats the initial decrease in blood flow gave place to hyperemia, Po(2) increased. In rats receiving cyclooxygenase inhibitor indomethacin no convulsions were observed, blood flow and Po(2)were lower than in controls. Our results indicate that indomethacin prevents hyperemia and alleviates oxygen convulsions under conditions of hyperbaric oxygenation.