Heart failure of various etiologies, including diabetic cardiomyopathy (DCM), is a global problem. However, the features of DCM pathogenesis, including the role of the T-tubular system in this process, are not fully understood. The available literature data on T-system remodeling in diabetic rodent models are contradictory, with changes in this system being demonstrated in some of them already at the prediabetic stage. So, this work was aimed to assess changes in the T-system in a rat model of metabolic syndrome (MS) that precedes type 2 diabetes mellitus. MS was induced in Wistar rats by a high-carbohydrate (HC) and a combined high-carbohydrate high-fat (HCHF) diets for 10 weeks. The parameters to be finally estimated were body, abdominal fat, and heart weights, as well as fasting plasma glucose levels measured by a glucose tolerance test (GTT). The structure of the T-system was examined via confocal microscopy in isolated hearts stained with DI-8-ANEPPS. HCHF-fed rats developed more severe MS since their body and abdominal fat weights, as well as fasting plasma glucose levels, were significantly higher compared to the controls; moreover, GTT revealed the signs of glucose tolerance. HC-fed rats were characterized by a moderate MS, as manifested only in an increase in abdominal fat weight. The structural correlates of T-system remodeling were also found in HCHF-fed rats only, as manifested in a significant increase in the average interval between the rows of T-tubules. These findings differ from our results obtained in a model of type 1 prediabetes and diabetes. Thus, T-system remodeling in rat cardiomyocytes begins already at the stage of HCHF-induced MS and proceeds similarly to that described for type 2 diabetes, but differs from that in type 1 prediabetes and diabetes, suggesting different pathways of DCM pathogenesis in different diabetic types.

Rats kept on a high-fat/high-sucrose diet (HFSD) for 10–12 weeks demonstrated the development of hyperglycemia and signs of visceral obesity. Compared to the control, extracellular action potentials (eAP) of subepicardial myocytes of the left ventricle (LV) of HFSD rats characterized by a significantly increased fraction of signals with a pronounced afterhyperpolarization (AHP) phase and an accelerated decline. Local delivery of apamin (a blocker of small conductance Ca2+-activated K+ channels (IKCa, SK channels) to the eAP registration cite at a concentration of 500 nM in the solution inside the pipette was accompanied by suppression of the AHP phase and prolongation of the eAP decline. The obtained data suggest that HFSD leads to an increase in the expression and/or activity of SK channels and, as a result, to the development of AHP and shortening of eAP in epicardial cardiomyocytes of the LV of the rat heart.

The results of the study of the applicability of various methods for calculating the values of the “generalized conductivity” of heterogeneous systems for predicting the dielectric constant of composite materials based on a polymer matrix and a filler are presented. To predict the dielectric constant of a material with a disordered filler arrangement, it is recommended to use the formula logε = ∑_i = 1^n Θ_i 1ptlog 1ptε_i , where n is the number of components, ε i is the dielectric constant of the i th component, and Θ i is the relative volume concentration of inclusions in the mixture. Consideration of the calculation results showed that, for composites with titanium dioxide as a filler, the calculated value of ε closest to the observed one is obtained when using the dielectric constant of titanium dioxide perpendicular to the optical axis (with the layers oriented perpendicular to the electric-field lines) (ε = 89). For composites with fibrous fillers, the calculated results can be interpreted as evidence that fibrous fillers in the composite are located mainly perpendicular to the direction of the applied electric field during the measurement.

The results of studying the effect of thermal-treatment modes and finishing conditions on the rupture strength of woven-glass tapes and fiberglass fabrics and electrical insulation manufactured from them are reported. It is shown that the complete removal of the oiling agent “wax emulsion” from the surface of glass tapes is attained after stepwise thermal treatment at 250–400°C, but the rupture strength decreases by 80

This paper describes the influence of hydrofluoric acid and its vapors on polymeric materials of various chemical nature. We establish that, under the long-term impact by hydrogen fluoride, the electrical characteristics, especially the specific surface electrical resistance of fiberglass with epoxy–phenolic or epoxy binder, deteriorate. The fiberglass mechanical strength passes through a minimum. The reinforcing material nature (polyester or glass fabric) does not significantly affect the electrical characteristics of the reinforced materials. The degree of hydrogen-fluoride impact on the fiberglass may be reduced by protecting the surface with polyepoxy and polymethylphenylsiloxane coatings.

The role of small conductance (SK) Ca2+-dependentpotassium channels in pathogenesis of diabetic cardiomyopathy remainsuncertain. In our studies in the rat model of streptozotocin-inducedtype 1 diabetess mellitus (STZ-DM1) a significant increase abovecontrol in the prevalence of extracellular action potentials (eAP)recorded from isolated heart left ventricles and terminating witha prominent phase of after-hyperpolarization was observed. In experimentswith local delivery to the site of recording of several tested potasssiumchannel blockers suppression of this phase of eAP after hyperpolarizationwas achieved only with application of apamin, the selective SK channelinhibitor. These data suggest that eAP afterhyperpolarization phaseis associated with activation of SK channels and that activity and/orexpression of these channels is increased in epicardial cardiomyocytesof left ventricles of STZ-DM1 rat hearts.

In this paper, we present a study of products obtained using various technological processes of forming laminated insulation by the winding method. The description of technological processes, the experimental setup, and methods for determining the dielectric strength of samples is given. A comparative analysis of samples obtained by different winding methods was performed, and the best method for manufacturing insulation was revealed.

Experimental data are presented concerning the changes in the characteristics of different polymeric electrical insulating compounds after a rather long holding in water and salt solutions at room temperature and 80°C. It has been found that the water absorption level of thermosetting compounds, as well as the worsening of their electrical properties, such as specific bulk electrical resistance and dielectric loss tangent dielectric permittivity under the action of water–salt media, is determined by the chemical nature of these polymers. The prolonged holding of epoxy compounds in salt solution at a normal and at an elevated temperature leads to water absorption lower than 1% and does not exert any significant effect on the electrical characteristics thereof. The holding of polyurethane compounds in a salt solution leads to a more than a twofold increase in water absorption compared to the epoxy compounds and to such a dramatic change in their electrical characteristics that it makes it impossible to use some of these compounds as insulating materials for manufacturing products that are to be exposed to water and water–salt solutions. The low water resistance inherent in polyurethane compounds and other nitrogen-containing polymers can be caused by a low hydrolytic resistance of the C–N bond occurring in the structure thereof. It is shown that water transpenetration through the layer of the SPB-KhP-80 polyurethane elastomer is quite possible.

Left ventricles (LV) of isolated hearts of the control rats (n = 7) and rats injected with streptozotocin (STZ; n = 21) were studied on the four-week post-injection term using 5-µm tip (O.D.) glass extracellular microelectrodes. STZ-rats that maintained hyperglycemia by the time of the study (random glucose > 11 mM; n = 3) were designated as diabetic animals (diabetes mellitus group; STZ-DM). Remaining STZ-rats (n = 18) were designated as normoglycemic rats (STZ-NG group). In control and in STZ-rat hearts two main types of sinus rhythm action potentials (AP) of epicardial ventricular myocytes could be recorded: signals characterized by a single (AP1) or double negative peaks (AP2). Respective time parameters of AP1 (rise time, and 50% and 90% decay times (T50 and T90) not differed between studied groups of rats. However, T50 of AP2 of LV myocytes of STZ-NG and STZ-DM rats were statistically significantly longer than T50 of AP2 recorded in control rat hearts. Furthermore, in 28% of STZ-NG and in 67% of STZ-DM rat hearts additional type of AP (AP3) featuring a complex, multi-peak negative phase and prominent positive phase of after-hyperpolarization were recorded. Appearance of AP3 was associated with a proportional decrease in the relative frequency of AP2 recordings (from 80-85% to 55-60% of all recordings). Frequency of AP1 recordings remained stable, 15-20% in all experiments in all groups of rats. Tentatively, observed in this study modulation in electrical activity of ventricular myocytes of STZ-rat hearts results from structure-functional changes in organization of the T-system of these myocytes. Regardless of validity of this suggestion, it is important that changes in electrogenesis of cardiomyocytes develop fast (1 month) not only in STZ-DM rats, but also in hearts of STZ-rats with normal or moderately increased blood glucose levels, which may be considered as the state equivalent to the state of early prediabetes.

Action potentials (APs) were recorded extracellularly from ventricular and atrial cardiomyocytes using isolated rat heart preparations and narrow-tipped (5-µm O.D.) recording pipettes. The negative phase of the AP waveform in ventricular cardiomyocytes exhibited a prolonged and, in about 60% of records, double-peak AP deflection, while that of APs in atrial cardiomyocytes regularly consisted of a single and relatively short peak. Confocal imaging and Monte-Carlo simulations suggest a stochastic variation in the number of t-tubule mouths under the lumen of randomly positioned extracellular recording pipette as the leading determinant of both, between and within, ventricular/atrial AP waveform variations.

The resilience of adhesive compounds in water—salt media was shown experimentally to depend on the nature of the bonding surfaces, as well as on the chemical peculiarities of adhesives. Unlike compounds based on epoxy resins and anhydride hardeners, adhesive compounds based on epoxy resins and aliphatic amine hardeners are unsteady in water-salt media. The resilience of systems on the basis of polyurethane adhesives to the water-salt environment is sensitive to the adhesive structure and may vary in a very broad range.

The paper addresses developmental features of the cerebrovascular reaction to functional tests as studied in volunteers of different ages without any signs of cerebrovascular pathology. Using transcranial Doppler sonography, it was shown that a significant decrease in the degree of manifestation of the cerebrovascular response to dosated functional loads occurs with age. A study of developmental features of this reaction to functional tests caused by autonomic regulation allowed distinguishing four types of its implementation: highly reactive, reactive, areactive and paradoxical. The data obtained support the informational significance of transcranial Doppler sonography and cerebrovascular reactivity for the identification of early changes in the state of the cerebrovascular system and its adaptive and compensatory abilities.

The chemical resistance of hardened epoxyisocyanate compound to alkalis, acids, sodium carbonate, and chloride solutions, as well as to hot water, is examined. According to the test results, the compound can be classified as a chemically resistant substance and recommended for application in the insulating systems of electrical machines that operate under conditions with increased chemical contamination, as well as for electrical machines used in seagoing ships.

The technological and operational properties of epoxy-izocyanate compound are described in this article. It is shown that the technological properties of this compound, such as viscosity and time of gelation, can vary largely. A hardened compound has very high operational characteristics of up to 220–240°C. The variability of the application of epoxy-izocyanate compound for creating high-heat-resistant systems of electric insulation is shown.

The mechanism of formation of rhythmic, slow-wave oscillations in the craniospinal cavity were studied. Synchronous bioimpedance traces were made of the head and lumbosacral part of the spine in five healthy young subjects at rest and during voluntary breath-holding; these reflect changes in the ratios of blood and CSF volumes in these parts of the craniospinal space. Computer amplitude-frequency and spectral analysis of the data (Macintosh G-4, Chart-5.2) demonstrated slow (6–12 cycles/min) and rapid (pulsatile) oscillations in different directions in the cranial and lumbosacral areas. These data suggested a hemoliquorodynamic hypothesis for the craniosacral rhythm. The pulsatile and slow-wave oscillations of cerebrovascular tone and intracranial pressure evidently initiate to-and-fro displacements of the CSF in the caudal direction. The associated tonic contractions of the musculature of the lumbar part of the spine and the mobility of the sacrum are detected manually as the craniosacral rhythm.

A review has been carried out of electrical-insulating compounds of the H—C temperature classes in Russia and abroad. A lack of electrophysical data on hardened compounds at operating temperatures is noted. The results of tests of some compounds using procedures used in Russia are presented. The necessity of using compounds with low dielectric loss tangents for high-voltage insulation systems applied at higher temperatures is shown.

Biomechanical properties of the human skull affect its dynamic tensility (pliability or compliance) at changes of intracranial volume and pressure (ΔV/ΔP). The work substantiates a possibility of noninvasive and dynamic evaluation of cranial compliance by synchronous recording of transcranial dopplerogram of middle cerebral artery and cranial bioimpedance that provides information about pulsative changes of intracranial pressure and volume, respectively, with subsequent computer pattern and phasic analysis of these processes. The characteristic peculiarities of the cranial compliance at rest and during action of functional hemo- and liquorodynamic tests were traced in people of the middle (40–50 years) and elderly (70–85 years) age groups as compared with the young group (20–30 years). A relative decrease of this parameter has been revealed in the middle age group due to an increase of rigidity of skull bones and ligaments, which indicates a decrease of tolerance of the intracranial circulatory system. However, in the group of 70–85 years the compliance parameters rose due to an increase of intracranial liquor volume and activation of liquor circulation inside the craniospinal space, which is a compensatory mechanism for maintenance of the adequate brain circulatory-metabolic activity.