Supra-physiological membrane potential induced conformational changes in K+ channel conducting system of skeletal muscle fibers

The effects of a supra-physiological membrane potential shock on the conducting system of the delayed rectifier K(+) channels in the skeletal muscle fibers of frogs were studied. An improved double Vaseline gap voltage clamp technique was used to deliver stimulation pulses and to measure changes in the channel currents. Our results showed that a single 4 ms, -400 mV pulsed shock can cause a reduction in the K(+) channel conductance and a negative-shift of the channel open-threshold. Following the Boltzmann theory of channel voltage-dependence, we analyzed the shock-induced changes in the channel open-probability by employing both two-state and multi-state models. The results indicate a reduction in the number of channel gating particles after the electric shock, which imply possible conformational changes at domains that gate the channels proteins. This study provides further evidence supporting our hypothesis that high intensity electric fields can cause conformational changes in membrane proteins, most likely in the channel gating system. These structural changes in membrane proteins, and therefore their dysfunctions, may be involved in the mechanisms underlying electrical injury.     

Structure and energetics of Li/Na, Li/K, and K/Na bimetallic hexamers

A systematic study of neutral mixed clusters, Li_6?x Na _x , Li_6?x K _x and K_6?x Na _x (x = 0–6), was performed within the framework of density functional theory. The aim of this work is to explore the geometry variation and the energy change of homonuclear hexamers (Li₆ and K₆) induced by impurities. It is found that the geometry of bimetallic hexamers varies with their compositions. The geometries of resulting clusters show evolution from D_4h symmetry for Li₆ to D_3h symmetry for Na₆ and K₆. The stability of bimetallic hexamers has been also explained in terms of binding energy, excess energy, the second difference in energy, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps. It is found that replacing each Li–Li bond with Li–Na or Li–K bonds decreases the cluster stability, while replacing each K–K bond by K–Na leads to stability enhancement. Examining the cluster stability, excess energy and second difference in energy reveal that among studied bimetallic hexamers, Li₂Na₄ is the most stable mixed hexamer.     

Model and simulation of Na+/K+ pump phosphorylation in the presence of palytoxin

The ATP hydrolysis reactions responsible for the Na(+)/K(+)-ATPase phosphorylation, according to recent experimental evidences, also occur for the PTX-Na(+)/K(+) pump complex. Moreover, it has been demonstrated that PTX interferes with the enzymes phosphorylation status. However, the reactions involved in the PTX-Na(+)/K(+) pump complex phosphorylation are not very well established yet. This work aims at proposing a reaction model for PTX-Na(+)/K(+) pump complex, with similar structure to the Albers-Post model, to contribute to elucidate the PTX effect over Na(+)/K(+)-ATPase phosphorylation and dephosphorylation. Computational simulations with the proposed model support several hypotheses and also suggest: (i) phosphorylation promotes an increase of the open probability of induced channels; (ii) PTX reduces the Na(+)/K(+) pump phosphorylation rate; (iii) PTX may cause conformational changes to substates where the Na(+)/K(+)-ATPase may not be phosphorylated; (iv) PTX can bind to substates of the two principal states E1 and E2, with highest affinity to phosphorylated enzymes and with ATP bound to its low-affinity sites. The proposed model also allows previewing the behavior of the PTX-pump complex substates for different levels of intracellular ATP concentrations.     

Investigating the potassium interactions with the palytoxin induced channels in Na+/K+ pump

K(+) has been appointed as the main physiological inhibitor of the palytoxin (PTX) effect on the Na(+)/K(+) pump. This toxin acts opening monovalent cationic channels through the Na(+)/K(+) pump. We investigate, by means of computational modeling, the kinetic mechanisms related with K(+) interacting with the complex PTX-Na(+)/K(+) pump. First, a reaction model, with structure similar to Albers-Post model, describing the functional cycle of the pump, was proposed for describing K(+) interference on the complex PTX-Na(+)/K(+) pump in the presence of intracellular ATP. A mathematic model was derived from the reaction model and it was possible to solve numerically the associated differential equations and to simulate experimental maneuvers about the PTX induced currents in the presence of K(+) in the intra- and extracellular space as well as ATP in the intracellular. After the model adjusting to the experimental data, a Monte Carlo method for sensitivity analysis was used to analyze how each reaction parameter acts during each experimental maneuver involving PTX. For ATP and K(+) concentrations conditions, the simulations suggest that the enzyme substate with ATP bound to its high-affinity sites is the main substate for the PTX binding. The activation rate of the induced current is limited by the K(+) deocclusion from the PTX-Na(+)/K(+) pump complex. The K(+) occlusion in the PTX induced channels in the enzymes with ATP bound to its low-affinity sites is the main mechanism responsible for the reduction of the enzyme affinity to PTX.     

Alterations of transmembrane currents in frog atrial heart muscle induced by photoexcited gymnochrome A purified from the crinoid, Gymnochrinus richeri

The effects of gymnochrome A were tested on the electrical activity of the frog atrial heart muscle. Gymnochrome A (1-5 microM) did not alter the resting potential. Gymnochrome A (5 microM) slowed the initial depolarizing phase of the spontaneously beating action potential. Under voltage-clamp conditions gymnochrome A (5 microM) did not affect the electrical constant of the membrane and the kinetic parameters of the peak Na+ current (INa) recorded in the Ringer solution containing tetraethylammonium (2 mM) and Cd2+ (1 mM) but shifted the membrane potential at which the current both activated and reached its maximal value toward more negative membrane potentials. It did not alter the reversal potential for INa, indicating that the selectivity of the Na+ channels had not changed. These observations suggest that gymnochrome A binds to the membrane and shifts the activation of INa on the voltage axis by modifying the free negative fixed charges present at the membrane surface rather than by occupying a specific site on the Na+ channel. Photoexcited gymnochrome A transiently triggered an early outward current which lengthened the time-to-peak of INa and decreased its amplitude. In addition, photoexcited gymnochrome A blocked the background K+ current. This is, to our knowledge, the first time that such effects are reported on the cardiac muscle. These observations suggest that the photoexcitation of gymnochrome produces physico-chemical effects which lead to intracellular changes. Further experiments are required to determine their nature.     

Graphical analysis of K/Na/Rb-interferences in AES

Summary A graphical method for studying interferences of different types in binary systems is proposed. It is based on orthogonal decomposition of a data matrix resulting from signals for different concentration levels of both the element to be determined and the interfering element. The obtained (principal components like) plot of rows of this data matrix exhibits some characteristic features allowing easy interpretation in real examples. As an application the FAES determination of K, Na, Rb is studied.     

Some theoretical results on the behaviour of Na and K currents in excitable membranes under voltage waveforms of various shape and frequency

The ionic currents of an excitable membrane under low-intensity voltage waveshapes are studied on the basis of the equations of Hodgkin and Huxley (HH-model). Theoretical considerations show that, when the applied signals are small, the HH-model has an active behaviour, and that the ionic currents can be correctly computed if equivalent pump-fluxes are introduced. Some results are presented, which show non-trivial behaviour of the ionic currents when particular waveshapes and frequencies are chosen for the signals.     

The First Principles Calculations of the Interaction between Li,Na, and K Atoms and Silicene

Russian Journal of Physical Chemistry A - Interaction between Li, Na, and K atoms and autonomous silicene is investigated using the density functional theory. The energies of adsorption and bond...     

速效胃宁冲剂中钾钠钙镁含量分析

用原子吸收法测定了5批速效胃冲剂中钾,钠,钙,镁的含量,结果表明,该药物中钾,钠,钙,镁的含量均较丰富,本结果为探讨速效胃宁冲剂中宏量元素及疗效的关系提供了有用数据。     

冷暴露大鼠红细胞膜钠泵与细胞内钠／钾比值间相互关系的探讨

研究了大鼠冷暴露１～６周，红细胞膜（Ｎａ，Ｋ）－ＡＴＰａｓｅ及细胞内Ｎａ的变化，结果表明在整个冷暴露期间，红细胞膜（Ｎａ，Ｋ）－ＡＴＰａｓｅ酸及细胞内Ｎａ／Ｋ比值均显著高于对照组（Ｐ＜０．０５），红细胞膜（Ｎａ，Ｋ）－ＡＴＰａｓｅ酶与细胞内Ｎａ比值间有明显的相关性（γ＝０．９１７），提示借助于钠泵的离子运输是冷适应细胞产热的主要机制。     

513—Some theoretical results on the behaviour of Na and K currents in excitable membranes under voltage waveforms of various shape and frequency

The ionic currents of an excitable membrane under low-intensity voltage waveshapes are studied on the basis of the equations of Hodgkin and Huxley (HH-model). Theoretical considerations show that, when the applied signals are small, the HH-model has an active behaviour, and that the ionic currents can be correctly computed if equivalent pump-fluxes are introduced. Some results are presented, which show non-trivial behaviour of the ionic currents when particular waveshapes and frequencies are chosen for the signals.     

重度糖尿病患者血清中金属元素钾,钠,钙,镁的分析

对６０例重度中老年糖尿病患者进行了血清中钾、钠、钙、镁的含量测定，并与正常对照组进行了比较。     

Antiferromagnetism in MUO3 (M=Na,K,Rb) studied by neutron diffraction

Simultaneous refinements of X-ray and neutron powder diffraction patterns taken on the MUO₃ perovskite compounds with M=Na, K and Rb, were performed to reveal anisotropy in the temperature factors, mainly of oxygen. No anisotropic thermal motion was found.The magnetic ordering of the compounds has been investigated with low temperature neutron diffraction. It is found that all these compounds show G-type antiferromagnetic ordering with a similar, orthorhombic magnetic unit cell. The propagation vector could only be determined for the orthorombic NaUO₃ compound and was found to point in the z-direction. The refined magnetic moment for U⁵⁺ in these structures was found to be around .     

Experimental examination of the matrix effect in the flame emission spectrometry of K, Na, and Sr

Summary The interferences in the determination of K, Na and Sr by flame emission spectrometry due to different sample components have been studied according to a new methodology of investigation of the matrix effect. This methodology comprises the formulation of mathematical (polynomial) models approximating the relationship between a measured signal (e.g. emission) and the concentration of the sample components. The regression coefficients in these models are estimated on the basis of the results of measurements carried out on appropriate standard samples. Their composition results from such experimental plans as a 2ⁿ factorial, a 3ⁿ factorial and a rotatable composite design. The 3ⁿ factorial one was the basis for the formulation of high-degree polynomial models which appeared adequate in all the cases considered. Some general problems connected with the use of this methodology in flame emission spectrometry (FES) are also discussed.

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Experimentelle Untersuchung des Matrixeffektes bei der Flammenemissions-Spektrometrie von K, Na und Sr

Zusammenfassung Mit Hilfe einer neuen Untersuchungsmethodik wurden die störenden Einflüsse von Begleitsubstanzen auf die flammenphotometrische Bestimmung von K, Na und Sr untersucht. Das Verfahren besteht in der Aufstellung mathematischer (Polynom-) Modelle, die der Beziehung zwischen Meßsignal (z. B. Emission) und Konzentration des betreffenden Bestandteils angenähert sind. Die Regressionskoeffizienten in diesen Modellen wurden aufgrund von Messungen an geeigneten Standardproben berechnet. Deren Zusammensetzung ergab sich aus entsprechenden Versuchsplänen (2ⁿ- und 3ⁿ-faktoriell sowie ein Rotationsplan). Der 3ⁿ-faktorielle Plan diente als Grundlage zur Aufstellung von Polynom-Modellen höheren Grades, die allen untersuchten Fällen genügten. Einige allgemeinere Probleme in Verbindung mit der Anwendung dieser Methodik auf die Flammenphotometrie werden ebenfalls diskutiert.

     

Mass spectral determination of skeletal/cardiac actin isoform ratios in cardiac muscle

Skeletal and cardiac muscle contains actin isoforms that vary by two juxtaposed amino acids and two amino acid substitutions (Met299Leu and Ser358Thr). This close sequence homology does not allow cardiac and skeletal actin isoforms to be resolved in traditional SDS-PAGE analysis as the molecular weights (Deltamass = 32 Da) are not significantly different and the pIs are identical (5.2). Although cardiac actin is the predominant form in cardiac muscle, there appears to be a specific skeletal/cardiac actin ratio in a normal heart that may vary in a compromised or diseased heart. In an effort to ascertain the validity of this hypothesis we developed a mass spectrometric technique to measure the ratio of skeletal to cardiac actin. The technique involves purification of muscle actin and subsequent liquid chromatography coupled with electrospray ionization Fourier transform ion cylcotron resonance (LC/FTICR-MS) mass spectrometry. A 7 Tesla FTICR mass spectrometer was utilized to compare skeletal/cardiac actin isoform ratios. Additionally, a new dual electrospray ionization source was employed to determine accurate masses of the alpha-skeletal and alpha-cardiac actins.     

Systematic study of (Na n )2 dimer transient state in Na n +Na n collisions (n=8, 9, 19, and 20)

From distance dependent tight-binding molecular dynamics simulations, we systematically study the Na _n +Na _n collision dynamics around the first two closed shells (n=8 and 20). We investigate the stability of sodium cluster dimers (Na _n )₂, for many events with random relative orientation at finite temperature, various impact parameters and incident energies. We find that (Na₈)₂, (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ can exist during about 3000 fs in central collisions while they can exist up to about ten thousands fs in peripheral collisions with larger impact parameters in fusion mechanism at c.o.m energy per atomE _cm/n=0.025 eV. We observe that the lower the incident energy, the longer the lifetime of the cluster dimers in both central and peripheral collisions. There is no apparent difference in the dynamical stability of (Na₈)₂ and (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ although (Na₈)₂ and (Na₂₀)₂ are respectively slightly colder than (Na₉)₂ and (Na₁₉)₂ for the same incident energy per atom and the same impact parameter.     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

10-30T恒定磁场下碱金属原子的边界轮廓

孤立原子是具有球对称性的.如果将孤立原子置于磁场中,原子的边界半径必然会发生变化.根据原子边界轮廓理论模型,研究和计算了在10~30 T磁场强度下碱金属原子的边界轮廓,可供有关参考.     

1O～3O T恒定磁场下碱金属原子的边界轮廓

孤立原子是具有球对称性的.如果将孤立原子置于磁场中,原子的边界半径必然会发生变化.根据原子边界轮廓理论模型,研究和计算了在10～30 T磁场强度下碱金属原子的边界轮廓,可供有关参考.