A. A. Balakin

Slow force response and auto-regulation of contractility in heterogeneous myocardium.

Classically, the slow force response (SFR) of myocardium refers to slowly developing changes in cardiac muscle contractility induced by external mechanical stimuli, e.g. sustained stretch. We present evidence for an intra-myocardial SFR (SFR(IM)), caused by the internal mechanical interactions of muscle segments in heterogeneous myocardium. Here we study isometric contractions of a pair of end-to-end connected functionally heterogeneous cardiac muscles (an in-series muscle duplex). Duplex elements can be either biological muscles (BM), virtual muscles (VM), or a hybrid combination of BM and VM. The VM implements an Ekaterinburg-Oxford mathematical model accounting for the ionic and myofilament mechanisms of excitation-contraction coupling in cardiomyocytes. SFR(IM) is expressed in gradual changes in the overall duplex force and in the individual contractility of each muscle, induced by cyclic auxotonic deformations of coupled muscles. The muscle that undergoes predominant cyclic shortening shows force enhancement upon return to its isometric state in isolation, whereas average cyclic lengthening may decrease the individual muscle contractility. The mechanical responses are accompanied with slow and opposite changes in the shape and duration of both the action potential and Ca²⁺ transient in the cardiomyocytes of interacting muscles. Using the mathematical model we found that the contractility changes in interacting muscles follow the alterations in the sarcoplasmic reticulum loading in cardiomyocytes which result from the length-dependent Ca²⁺ activation of myofilaments and intracellular mechano-electrical feedback. The SFR(IM) phenomena unravel an important mechanism of cardiac functional auto-regulation applicable to the heart in norm and pathology, especially to hearts with severe electrical and/or mechanical dyssynchrony.

Multichannel extraction of charged species from liquid with use of track membranes

Abstract An extraction of negative charged species under electric field from liquid solutions into vacuum by use of poly(ethylene terephialate) track membranes has been investigated. The measurements of a total current at different voltages, applied between a liquid sample and a electrode in vacuum, has been carried out. In addition, an influence of an electrolyte concentration on the total current for the KI solution in glycerol has been studied. It is shown that a special feature of extraction of charged species from the channels of dielectric membranes is connected largely with on accumulation of charges on the vacuum surface of the polymer membrane. So, the current from dielectric membrane is controlled by several processes including formation of strong electric field near the liquid-vacuum interface, transport of ions along the channels to the interface and the field-assisted transition of charged species into vacuum.

Contribution of mechanical factors to arrhythmogenesis in calcium overloaded cardiomyocytes: Model predictions and experiments

It is well-known that Ca²⁺ overload in cardiomyocytes may underlie arrhythmias. However, the possible contribution of mechanical factors to rhythm disturbances in Ca²⁺ overloaded myocytes has not been sufficiently investigated. We used a mathematical model of the electrical and mechanical activity of cardiomyocytes to reveal an essential role of the mechanisms of cardiac mechano-electric feedback in arrhythmogenesis in Ca²⁺ overloaded myocardium. In the model, the following mechanical factors increased Ca²⁺ overload in contracting cardiomyocytes and promoted rhythm disturbances: i) a decrease in the mechanical load for afterloaded contractions; and ii) a decrease in the initial length of sarcomeres for isometric twitches. In exact accordance with the model predictions, in experiments on papillary muscles from the right ventricle of guinea pigs with Ca²⁺ overloaded cardiomyocytes (using 0.5-1 μM of ouabain), we found that emergence of rhythm disturbances and extrasystoles depends on the mechanical conditions of muscle contraction.

The length-dependent activation of contraction is equally impaired in impuberal male and female rats in monocrotaline-induced right ventricular failure.

The length‐dependent activation of contraction is attenuated in the failing myocardium of adult male rats. This pathological change is not seen in adult female rats, possibly because of a protective effect of sex hormones. The present study evaluated length‐dependent changes in isometric twitch, Ca2+ transient (CaT) and action potential (AP) in the right ventricular myocardium of impuberal healthy male and female rats (control) and in rats treated with a single injection of 50 mg/kg monocrotaline (MCT). Compared with sex‐matched control rats, MCT‐treated male and female rats exhibited increased right ventricular weight (134% and 142% of control, respectively), decreased left ventricular weight (72% and 79%), twitch attenuation (48.8 ± 2.7% and 57.5 ± 1.2%) and prolongation (125 ± 3% and 127 ± 2%), CaT attenuation (37.8 ± 0.4% and 39.1 ± 1.1%) and prolongation (114 ± 1% and 116 ± 1%) and AP prolongation at 90% repolarization (195 ± 2% and 203 ± 1%). The MCT‐treated male rats exhibited a 50% lower integral magnitude and an approximately 25% larger time‐to‐peak ‘bump’ compared with control male rats. These parameters in MCT‐treated female rats tended to show similar changes to those seen in the control female rats, with no significant difference between the two groups. In all groups, integral magnitude and time‐to‐peak ‘bump’ increased with length. In conclusion, the length‐dependent activation of contraction was equally blunted in the failing right ventricular myocardium of impuberal male and female rats. This was related to changes in CaT and AP, which were similar between male and female rats. Therefore, puberty is necessary for manifestation of the protective effects of sex hormones on this remodelling.

Generation of an extraction electric field in an electromembrane ion source

A mechanism of generating an extraction field in an ion source in which a polymer track membrane with nanodimensional channels is used as an environment-vacuum interface is considered. A high electric field necessary for the effective extraction of ions from a liquid on the membrane surface into the gas phase is maintained by charging the vacuum surface of the membrane. Charging is provided by oppositely charged secondary ions resulting from the disintegration of primary cluster ions on the extraction electrode. A decrease in the source current observed when the vacuum surface discharges counts in favor of this mechanism. The extracted ion energy distribution in the neighborhood of the extraction zone is obtained by the retarding potential method. Various aspects of ion beam formation in the membrane ion source are discussed.

Polymer track membranes for extraction of ions from aqueous solutions at atmospheric pressure

The possibility of the application of the electromembrane technique for production of ions of biological molecules at atmospheric pressure is demonstrated. This technique has previously only been used for extraction of ions from liquids directly into vacuum. The membrane technique for ion extraction at atmospheric pressure was tested with both time-of-flight and Fourier transform ion cyclotron resonance mass spectrometers. The mass spectra of intact molecular ions obtained from aqueous solutions of peptides and proteins are presented. The possible mechanisms of non-destructive ion extraction are discussed. The new technique is promising for achieving absolute sensitivity (charging every analyte molecule) and for performing spatially-resolved analysis of liquid biological samples.

Thermalization of low energy electrons in liquid methylcyclohexane studied by the photoassisted ion pair separation technique

Abstract A spectral dependence of the charge carrier quantum yield in liquid methylcyclohexane was investigated on photoexcitation of geminate electrons at wavelengths between 425 and 867 nm. The electrons were produced by two photon ionization of the anthracene admixture with the UV laser pulse (wavelength 308 nm, duration about 20 ns) and, then, were excited by the dye laser pulse delayed for a time of 25 ns with respect to the UV one. The increase of photocurrent caused by an additional dye laser pulse action was observed as temperature decreased below 230 K. It has been found that the spectrum of the photocurrent enhancement in the range of dye laser radiation wavelengths from 425 to 867 nm is close to that of the trapped electron optical absorption. The increase of photocurrent has been attributed to photogeneration of “hot” quasi-free electrons arising from a photon absorption by geminate trapped electrons. Basing on the diffusion model of photostimulated ion pair dissociation, the thermalization length of 4.2–4.7 nm was determined for quasi-free electrons with an initial kinetic energy within the range from about 0.9 to 2.4 eV. The energy dissipation rate and effective mean free path were evaluated for the quasi-free electrons with the energy of about 1 eV in hydrocarbon matrix.

Ionization of solvent molecules by the field evaporation of ions from glycerol and ethylene glycol solutions

Using an electromembrane source, mass-spectrometric investigations into the field evaporation of ions from KI solutions in a water-glycerol mixture and in ethylene glycol are performed. The concentration of negatively charged solvent ions (deprotonated molecules) on the emitting surface of the liquid is determined. It is shown that, under the conditions of intense field evaporation of ions, the surface concentration of deprotonated glycerol and ethylene glycol molecules is several orders of magnitude higher than their equilibrium concentration in the absence of an electric field. The high concentration of solvent ions is associated with an increase in the autoprotolysis constant in a strong electric field.

Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.

Track-membrane-based interface for field evaporation of ions from polar solutions in the diffusion-drift regime

The possibility of realization of barrier-free field evaporation regime for ions from polar solutions in the conditions when the flux of ions from the liquid is limited by their diffusion and drift from the bulk to the surface is considered. The strength of the electric field extracting ions is estimated by simulating electric fields in an ion source with a track membrane as the interface with allowance for the sizes of channels in the membrane and their density. It is shown that when time-dependent electric fields are used, the regime of barrier-free field evaporation can be realized with an appropriate choice of geometrical parameters of the membrane.