Biomedical subjects

V G Ivkov

Publications and source records attributed to V G Ivkov.

At least 19 recordsLinked to original sources

PubMed2003

[The annual involution and regeneration of the thymus in hibernating animals and perspectives of its studies in gerontology and stem cell proliferation].

Data on a unique phenomenon of annual involution and neogenesis of thymus gland in hibernating animals are reviewed. In accordance with morphological findings, the annual thymus involution in hibernating animals is close to the age-dependent thymus involution occurring in all mammals once in a lifetime. In opposite, thymus involution in hibernating animals is totally different from the accidental involution. During hibernation, the thymus tissue is substituted by the brown fat tissue. In the spring, thymus gland neogenesis stats with intensive growth of epithelial tissue followed by lymphocyte infiltration and exhaustion of brown tissue. Morphological changes in the thymus gland within the annual cycle were compared with seasonal dynamics of structural and functional changes in peripheral lymphoid organs (spleen, lymphoglandular, peritoneal fluid). A general regularity was observed involving a decreased functional activity of immune cells in autumn, its sharp depression during winter hibernation, and obvious increase in summer with the onset of a season of animal activity. It is supposed that a sharp increase in the tumor necrosis factor (TNF) production observed during short-term awakenings in winter may serve an important link in this unique immune adaptation mechanism. The season changes in cellular TNF secretion suggest a mobilization of protective resources in hibernating animals in autumn and winter, i.e. in seasons when the thymus gland activity is depressed. The annual involution of thymus gland cannot be related to droppings in the environmental or body temperatures, as it comes long before their fall. Additionally, it is not related to ageing, as it occurs already in young hibernating animals. The role of hormones, including melatonine and corticosteroids, in mechanisms regulating thymus gland involution in hibernating animals is discussed.

Adaptation, Physiological↗

PubMed2001

Steroid-induced conformational changes of FITC-labelled sarcoplasmic reticulum Ca2+-ATPase.

Interactions between transmembrane and cytoplasmic domains of Ca2+-ATPase from sarcoplasmic reticulum (SR) have been studied. To affect the hydrophobic transmembrane domain, we used four amphiphilic steroids - esters of a dibasic acid and 20-oxypregnene. All four steroids contained cholesterol-like nuclei and differed by the structure of side chains. Steroids with carboxyl groups in the side chains inhibited the rates of ATP hydrolysis and Ca2+ transport, whereas a steroid without the carboxyl group did not appreciably affect Ca2+-ATPase function. Fluorimetric titration of FITC-labelled Ca2+-ATPase in SR vesicles by Nd3+ showed that steroids increased the apparent dissociation constant for Nd3+ bound to the hydrolytic site, the potency order of the steroids being the same as for the sterol-induced inhibition of the hydrolytic activity of Ca2+-ATPase. These results suggest structural changes in the active site. Ca2+ transport was inhibited more efficiently by steroids than the hydrolytic activity of the enzyme. This could be partially due to the increase of the membrane passive permeability induced by steroids, which, in turn, reflected the efficiency of the interaction of the steroids with lipid bilayers. The effects of the steroids were largely dependent on their amphiphilicity (the availability of polar groups in regions A and D), the structure of the side chains, and, possibly, on the distance between the molecular polar groups. We suggest that the inhibition of hydrolytic and transport functions of Ca2+-ATPase in the SR membrane is due to the interaction of the steroids with the transmembrane alpha-helical segments.

Adenosine Triphosphate↗

PubMed1992

Effects of pH, Ca2+ and lanthanides on conformation of the sarcoplasmic reticulum Ca(2+)-ATPase catalytic site.

The conformational changes at the ATP-catalytic site of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase have been studied by the fluorescence of the fluorescein 5-isothiocyanate (FITC) bound to the adenine subsite. The FITC-SR fluorescence parameters have been examined in the pH range 5.7-8.0 in the presence of EGTA, Ca2+ or Ln3+ (La3+, Pr3+, Nd3+, Tb3+, etc.). A quantitative method to calculate the equilibrium between the protein conformers is proposed on the basis of the fluorometric titration curve analysis. The distance Nd(3+)-FITC was estimated to be about 1 nm at pH 6-7 and 1.7 nm at pH 8 which can be interpreted as an increase of the distance between the nucleotide and phosphorylation domains of Ca(2+)-ATPase in alkaline media. These studies suggest that the ligand-stabilized E1-form of Ca(2+)-ATPase can exist in two conformational states with the closed and opened interdomain cleft in the pH range 5.7-8.0. The pH-dependence of the ratio of these states correlates with that of the E1----E2 equilibrium without ligands. These dependences were approximated by simple Henderson-Hasselbach equations with pK 7.0 +/- 0.1, i.e. the transition between two protein conformations is probably governed by one proton dissociation.

Animals↗

PubMed1991

Detection of structural defects in phosphatidylcholine membranes by small-angle neutron scattering. The cluster model of a lipid bilayer.

The oriented DPPC multilayers hydrated by D2O have been studied by a small-angle neutron scattering method in the Guinier range, and the gyration radius of the structural inhomogeneities has been estimated at about 29 A. They are interpreted as the annular defects between adjacent clusters uniting the all-trans chain 'segments' adjacent to the polar head group regions. The angle of the 'segment' tilt is determined by the hydrated polar group area (59.2 A2 for DPPC bilayers) and has been estimated to be about 44 degrees under the given experimental conditions. The hydrocarbon interior of a bilayer can be suggested as a 'sandwich' that is formed by two clustered layers (approx. 7 A of the thickness) and the central disordered (liquid) layer. The average cluster size along the bilayer surface is estimated to be approx. 24 A which correlates with the estimations of the short order region dimensions from the halfwidth of the X-ray 'packing' reflex (4.6 A)-1. The average interchain separation of approx. 5 A and the average cross-section area of a chain in a cluster (21.4 A2) were estimated from the reflex position and the chain cross-section geometry. The total volume of defects and the fraction of a bilayer surface occupied by them were estimated too.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

Cholesterol oxidation on fluorocarbon emulsion surface leads to the formation of 7-peroxycholesterol.

Formation of biologically active oxidized derivatives of cholesterol as a result of its oxidation on the surface of fluorocarbon emulsions was studied. A single product of cholesterol oxidation, 7-peroxycholesterol, was found. It was shown that 7-peroxycholesterol and its derivative 7-keto-cholesterol inhibit the rosette formation between human T-lymphocytes and sheep erythrocytes. These substances exert a strong cytostatic action on the growth of procaryotic and eucaryotic cell cultures. Thus, oxidative modification of blood plasma components on the surface of fluorocarbon emulsion particles with the formation of highly active compounds must be taken into account when using the fluorocarbon emulsions in medicine.

Acholeplasma laidlawii↗

PubMed1990

[Formation of biologically active substances during cholesterol oxidation on the surface of fluorocarbon emulsions].

Oxidative modification of cholesterol on the surface of fluorocarbon emulsions was studied. The oxidation yielded one primary product--7-peroxycholesterol. It was shown that the obtained cholesterol C7 derivatives possess a high biological activity. It was concluded that the possibility of oxidative modification of plasma substances on the surface of fluorocarbon emulsion particles with the formation of highly active compounds must be taken into account when using the fluorocarbon particles in medicine.

Cholesterol↗

PubMed1987

Interaction of the voltage-sensing fluorescent probe diS-C3-(5) with dipalmitoylphosphatidylcholine liposomes.

The interaction of the probe diS-C3-(5) with dipalmitoylphosphatidylcholine (DPPC) liposomes has been studied using fluorescence and differential scanning calorimetry (DSC). The partition coefficients (K) of the probe for the lipid and the aqueous phase (in terms of molar part units) were (1.20 +/- 0.4) X 10(6) at 45 degrees C and (0.50 +/- 0.07) X 10(6) at 23 and 36 degrees C. In terms of volume concentration units, these values correspond to Kp = (2.88 +/- 0.10) X 10(4) and Kp = (1.20 +/- 0.17) X 10(4), respectively. DSC thermograms were practically identical both for large unilamellar and multilamellar liposomes. The main transition peak remained practically unchanged over the entire range of the probe concentrations used. The pretransition could be observed up to maximal probe concentrations applied and it widened and shifted from 35.4 degrees C in pure DPPC to approximately 32 degrees C at a probe/lipid ratio of 0.027. These results suggest that in both quasicrystalline and liquid crystalline lipid bilayers the probe molecules are included in "defects" between structurally ordered microregions (microdomains or clusters). The dependence of the fluorescence response on the transmembrane potential in a suspension of unilamellar DPPC vesicles suggest that the equilibrium thermodynamic model is valid for liquid crystalline bilayers.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1984

Mechanism of fluorescent response of the probe diS-C3-(5) to transmembrane potential changes in a lecithin vesicle suspension.

The dependence of both the magnitude and the sign of fluorescent responses of the probe diS-C3-(5) in egg lecithin vesicle suspensions on the magnitude of the inside-negative transmembrane potential and on the total probe concentration in the sample volume has been studied. Results were compared with theoretical calculations made on the basis of the equilibrium thermodynamic model suggested earlier as well as on the observed concentration dependence of the probe fluorescence in aqueous media and membranes. It was shown that transmembrane potential results in a redistribution of the probe between the aqueous and the membrane phases and in the membrane interior. The model calculations showed that the probe concentrations in the external aqueous medium and in the outer lipid monolayer of a vesicle significantly decrease. At the same time, the dye concentration in the inner membrane monolayer increases significantly, which should lead to a marked quenching of the dye fluorescence. The changes in the fluorescence and absorption spectra are well explained in terms of the proposed mechanism. The highest responses of diS-C3-(5) to changes of the transmembrane potential were observed in a shorter wavelength region of the fluorescence spectrum at the probe to lipid ratios in membrane of 15-20 moles of probe per 1000 moles of lipid. In the longwave region, the increase in fluorescence is not an obligatory indication of a decrease in the transmembrane potential and, under certain conditions, this process can take place when the transmembrane potential increases. The generation of a quasi-equilibrium diffusion transmembrane potential results in an increase in the average probe concentration in membranes if the signs of the probe charge and the potential inside the vesicles are opposite. Thus, the "on-off" mechanism, working under conditions of steady-state processes, is not valid under equilibrium conditions.

Benzothiazoles↗

PubMed1984

Redistribution of positively charged probes in membrane suspension under the action of transmembrane potential.

The distribution of amphiphilic and hydrophobic positively charged probes in suspensions of closed membrane vesicles was analysed by the methods of equilibrium thermodynamics. Two versions of the probe location in the membranes are discussed: near the boundary between the polar and hydrocarbon regions, and in the centre of the hydrocarbon region of a lipid bilayer. It is shown that, in the first case, the action of the inside-negative transmembrane potential results in an increased average probe concentration in the lipid phase and in a significant redistribution of the probe in the membrane interior. An inside-positive transmembrane potential causes a decrease in the average probe concentration in membranes, the probe being redistributed in the membrane bilayer. If the probe is sited in the centre of the hydrocarbon layer, the transmembrane potential evokes only an increase or decrease in the probe concentration in membranes at a negative or positive sign of the potential inside the vesicles.

Coloring Agents↗

PubMed1983

The behavior of the fluorescent probe diS-C3-(5) in membrane and aqueous media.

Based on an analysis of back fluorometric titration data a partition coefficient, Kp = (5.70 +/- 0.95) x 10(4), and partition constant, K = (2.37 +/- 0.43) x 10(6), were found for the probe diS-C3-(5) in egg lecithin vesicle suspension. The relative probe quantity in an aqueous medium and in liposomes was calculated using these parameters. The number of chromophore states in this system was computer-analysed and it was shown that the probe fluorescence could be described by two fluorescing dye forms, aqueous and membrane monomers. The dependence of fluorescence intensity on the probe concentration was studied in various salt media, and a dimerization (association) constant Ka = 5 x 10(4) mol -1 . l in the buffer, and Ka = (8.1 +/- 1.5) x 10(4) mol-1 . l in 0.1 or 0.2 mol/l salt medium (KCl or NaCl) was found. From the fluorescence and absorption data critical concentrations of the onset of large probe aggregate formation were calculated for various aqueous media. The concentration dependence of the probe fluorescence in the membrane phase was calculated. The critical concentration of interaction characterizing the efficiency of the fluorescence concentration quenching processes (CCI) was found to be approx. 5-6 mol probe per 1000 mol lipid. The top probe concentration in a membrane (the "saturation" concentration) was estimated from the slope of the initial linear parts of the back fluorometric titration curves, and was found to be equal to (59 +/- 13) mol probe per 1000 mol lipid.

Benzothiazoles↗

PubMed1978

Voltage-induced reflectivity relaxation of bilayer lipid membranes: on changes of bilayer thickness.

Temporal and voltage-induced changes of reflectivity (R), the optical phase difference in transmitted polarized light, of tension and total capacity of bilayer lipid membrane (BLM) were studied. The membranes were mainly formed from total brain phospholipids (TP) in n-alkanes. 1) Reflectivity of "black" regions of films made of TP in decane and hexadecane decreases by several percent with a time constant (tauR) of about 30 min, whereas that of membranes with hexane and heptane does not depend on time (with an accuracy up to 1--2%). The BLM tension decreases appreciably in the course of time and reaches its steady-state value in tens of minutes after complete blackening of the membrane. 2) Under prolonged (up to tens of minutes) action of voltage (V) no R changes of BLMs with hexane, heptane, and hexadecane were revealed at a noise level of 0.2%. Blms with decane usually respond to voltage application, first by a rapid (jump-like) and then by a slow decrease of R with a value spread from 0.2% to 3%. 3) With higher amplitude and temporal resolutions of the signal (signal averaging method) it can be seen that after voltage jump R decreases down to a new steady-state value: at V = 100 mV, deltaR/R = -(2--4) . 10(-4) and tauR approximately 0.1 msec for BLMs from TP in heptane, and deltaR/R = -(3--6) . 10(-2) and tauR approximately 2 msec for BLMs from oxidized cholesterol in decane. It is shown in the latter case that the great value of deltaR/R is due to the contribution of invisible microlenses. In all the cases deltaR approximately V2. 4) It is concluded that at voltage jump a bilayer first becomes thinner due to volumic compression of its hydrocarbon core; then it spreads with a time constant of the order of 0.1 msec, getting thinner until a new equilibrium state is reached. Complete change of bilayer thickness is detah/h approximately -10(-4) at 100 mV.

Alkanes↗

PubMed1977