PubMed Health⌕ Search

Biomedical subjects

S L Aksentsev

Publications and source records attributed to S L Aksentsev.

At least 19 recordsLinked to original sources
PubMed1998

Na+/H+ exchange in vascular smooth muscle cells is controlled by GTP-binding proteins.

This study examines the involvement of GTP-binding proteins (Gps) in the regulation of Na+/H+ exchange and Ca2+ influx, which are increased in vascular smooth muscle cells from spontaneously hypertensive rats. Gp activity was modulated by fluoride, GTPgammaS, GDPbetaS, and antisense oligodeoxynucleotides complementary to conserved regions of the alpha- and beta-subunits of Gps (alpha-comm and beta-comm, respectively). Beta-adrenergic-induced Gs-mediated cAMP production was used as a positive control to estimate the efficiency of these compounds. Na+/H+ exchange, measured as ethylisopropyl amiloride-sensitive 22Na influx, was activated by 5- to 6-fold by a 30-minute preincubation of cells with 10 mmol/L NaF with a K0.5 for NaF of approximately 13 mmol/L. In contrast, no activation of 45Ca influx was observed under preincubation of vascular smooth muscle cells with NaF in Ca2+-free medium, whereas at [Ca2+]o >0.5 mmol/L, simultaneous addition of 45Ca and 10 mmol/L NaF led to sharply increased isotope uptake. NaF-induced 45Ca influx did not reach saturation up to 3 mmol/L [Ca2+]o and 20 mmol/L NaF and was correlated with the formation of calcium-fluoride complexes measured by light scattering. GTPgammaS increased basal cAMP production and Na+/H+ exchange, whereas GDPbetaS decreased isoproterenol-induced cAMP production and Na+/H+ exchange. Alpha-comm reduced whereas beta-comm augmented isoproterenol-induced cAMP production by 70%. Both oligodeoxynucleotides decreased basal Na+/H+ exchange by 40% to 50%. NaF-induced Na+/H+ exchange was not sensitive to alpha-comm but was inhibited by 60% in beta-comm-loaded cells. Neither basal nor NaF-induced 45Ca uptake was affected by GTPgammaS, GDPbetaS, and the oligodeoxynucleotides. Our results show that 45Ca uptake is activated by NaF in vascular smooth muscle cells by nonspecific accumulation of calcium-fluoride complexes and is not related to modification of Gps. On the contrary, the Na+/H+ exchanger is controlled by Gps, and Gp beta-subunits are involved in [Ca2+]o-independent activation of this carrier by NaF.

Aluminum Chloride↗
PubMed1998

Effect of calcium on the energy status of rat brain synaptosomes under acidosis.

Incubation of rat brain synaptosomes at pH 6.0 in Ca2+-containing medium is associated with a decrease in the ATP content and the rate of oxygen consumption. ATP/ADP ratio decreased from 6.6 +/- 0.24 at pH 7.4 to 3.2 +/- 0.17 at pH 6.0. The content of 86Rb+ and [3H]tetraphenylphosphonium measured at pH 7.4 did not change after preincubation at pH 6.0, indicating the absence of lesion of synaptosomal plasma membranes and intrasynaptosomal mitochondria. Incubation with 1 mM EGTA in Ca2+-free medium as well as addition of 1 mM ouabain or 10 microM ruthenium red prevents the effect of acidosis. Similar results were obtained when 5 mM pyruvate was used as a mitochondrial substrate instead of glucose. It is suggested that acidosis-induced decrease in the ATP level is associated with the increase in Ca2+ concentration in the cytoplasm and its transport into mitochondria. Ouabain reverses this process due to activation of Na+/Ca2+ exchange.

Acidosis↗
PubMed1997

Hypoosmotic shock activates Ca2+ channels in isolated nerve terminals.

Influence of hypotonic swelling on Ca2+ (45Ca2+) uptake in rat brain synaptosomes was studied. A decrease in medium osmolality from 310 to 260-180 mOsm led to a progressive stimulation of 45Ca2+ accumulation. The effect was blocked by verapamil (IC50 = 5 microM), CoCl2 (IC50 = 58 microM) and retained at a fixed concentration of external sodium indicating the involvement of Ca2+ channels rather than Na+/Ca2+ exchange in swelling-induced Ca2+ influx. The populations of calcium channels observed in hypoosmotic and depolarizing conditions are different in three aspects: (i) kinetics of 45Ca2+ entry; (ii) insensitivity to dihydropyridines and omega-conotoxin GVIA; (iii) insensitivity to preliminary depolarization by high potassium. The effects of swelling and depolarization on Ca2+ uptake were additive. No change in membrane potential monitored with diS-C3-(5) was recorded during synaptosome hypotonic swelling. The results suggest the existence in synaptosomal plasma membrane of volume-dependent calcium-permeable channels with properties distinct from those of the voltage-dependent calcium channels. Activation of these channels may constitute an early event in volume regulation of nerve terminals in anisoosmotic conditions.

Animals↗
PubMed1997

[The regulation of cell volume: the mechanisms of intracellular signalling].

The mechanisms of intracellular [correction of intercellular] signalling responsible for cell volume regulation are elucidated in the 2nd part of the review. Data on a nature of the "volume" sensor and signals acting on it, the properties of structures and mechanisms regulating the cell volume, are discussed as well as genetic regulation of the cell volume responses.

Animals↗
PubMed1996

Swelling-induced activation of Na+,K+,2Cl- cotransport in C6 glioma cells: kinetic properties and intracellular signalling mechanisms.

Swelling of C6 glioma cells in hypotonic medium (180 mOsm) results in two- to three-fold activation of K+ (86Rb+) influx suppressed by 10 microM bumetanide. Bumetanide-sensitive transport of 86Rb+ is dependent on extracellular K+, Na+ and Cl- both in iso-osmotic conditions and under hypo-osmotic shock, supporting the notion that it is mediated by Na+,K+,2Cl- cotransport. Inhibitors of protein kinase C (10 microM polymyxin B and l microM staurosporine) had no significant effect on basal cotransport but reduced its hypotonic stimulation by 70-80%. Similar results were obtained with calmodulin antagonist R24571 (10 microM), indicating Ca2+/calmodulin-dependence of the process. Influence of polymyxin B and R24571 was not additive. Swelling-activated Na+,K+,2Cl- cotransport was also suppressed by protein kinase C activator PMA (l microM). By contrast, preincubation of cells with inhibitors of protein phosphatases (100 microM vanadate, 5 mM fluoride and 0.5 microM okadaic acid) activated greatly the bumetanide-sensitive 86Rb+ uptake in isotonic conditions, while a subsequent hypotonic swelling led to smaller or no increment. These results indicate the involvement of Ca2+/calmodulin-dependent staurosporine/polymyxin B-sensitive protein kinase other than protein kinase C in swelling-induced activation of Na+,K+,2Cl- cotransport in glial cells.

Bumetanide↗
PubMed1995

Effect of proteolysis on the state of lipid phase in rat brain synaptosomal membranes.

Enzymatic proteolysis of the proteins of synaptic membranes has been found to be accompanied by the promotion of lipid peroxidation probably mediated by the liberation of membrane-bound iron. As fluorescent probes pyrene and diphenylhexatriene show, the microviscosity and micropolarity of membrane lipid phase rise as a result of lipid peroxidation. Different structural changes induced by proteolysis are displayed under inhibition of lipid peroxidation. Thus, the microviscosity of the bulk lipid phase appears to be lowered and the annular lipid microviscosity raised. Another explanation of the fluorescent data for annular lipids is the exclusion of pyrene molecules from this lipid pool, leading to a reduction of the probe local concentration. The changes observed in membrane lipid phase are considered as primary structural effects of proteolysis, not mediated by a phospholipase activation.

Animals↗
PubMed1994

Swelling-induced K+ influx in cultured primary astrocytes.

The effect of swelling of cultured primary astrocytes from rat brain in hypotonic medium on K+ influx has been studied. A decrease in osmolality from 310 to 180 mOsm increased the activity of sodium pump (ouabain-inhibited 86Rb+ influx) and Na+,K+,2Cl- cotransport (ouabain-insensitive bumetanide-inhibited 86Rb+ influx) by 70 and 35%, respectively. It is suggested that activation of these transport systems makes it possible to retain a high potassium concentration in the cells under regulatory volume decrease.

Animals↗
PubMed1994

Osmotic regulation of sodium pump in rat brain synaptosomes: the role of cytoplasmic sodium.

The effect of hypoosmolality of incubation medium on the rat of ouabain-sensitive 86Rb+ transport in rat brain synaptosomes was studied. A decreased osmolality from 310 to 250 mOsm increased the rate of 86Rb+ uptake from 3.72 to 6.23 nmol/mg of protein min. To evaluate the involvement of cytoplasmic sodium in sodium pump stimulation inhibitors of ion channels and transport pathways able to increase [Na+]in were used. Tetrodotoxin (1 microM), amiloride (0.5 mM) and verapamil (0.1 mM) had no influence on the osmotic response of the sodium pump. The decrease of sodium concentration in incubation medium to 15 mM, leading to a practical loss of its transmembrane gradient, did not abolish stimulation of pump. No increase in 22Na+ influx or intrasynaptosomal sodium content was registered at hypotonic conditions. It is suggested that osmotic regulation of Na+,K(+)-ATPase is not connected with an increase of internal sodium through opening of sodium channels, or with activation of other membrane sodium-transporting systems.

Animals↗
PubMed1993

Kinetics and peculiarities of thermal inactivation of volume-induced Na+/H+ exchange, Na+,K+,2Cl- cotransport and K+,Cl- cotransport in rat erythrocytes.

The kinetics of the volume-dependent activation of Na+/H+ exchange, Na+,K+,2Cl(-)-cotransport and K+,Cl(-)-cotransport in rat erythrocytes was studied. The significant increase in the rate of Na+/H+ exchange is observed within 15 min after hypertonic shrinkage while the maximum transport rate is reached by 20 min. A delay of about 5 min was found in activation of Na+,K+,2Cl(-)-cotransport, the maximum transport rate being reached 10 min after shrinkage. Activation of K+,Cl(-)-cotransport by hypotonic swelling was registered within 10 min after cell swelling, with a simultaneous achievement of the constant transport rate. Preincubation of cells at 49 degrees C has no effect on the basal Na+/H+ exchange and Na+,K+,2Cl(-)-cotransport but suppresses the activation of these systems by osmotic shrinkage. On the contrary, the rate of K+,Cl(-)-cotransport in isosmotic medium is raised 10-fold after preincubation at 49 degrees C. The thermal treatment at 49 degrees C blocks the activation of K+,Cl(-)-cotransport by swelling. On the basis of the data on thermal denaturation of spectrin at the same temperature it was suggested that the cytoskeleton of erythrocyte membrane is involved in volume regulation of the ion-transporting systems and that the molecular mechanisms which underlie the activation of Na+/H+ exchange, Na+,K+,2Cl(-)-cotransport and K+,Cl(-)-cotransport are essentially different.

Animals↗
PubMed1993

Effect of gamma-irradiated carbohydrates on isolated synaptic membranes.

The effect of gamma-irradiated solutions of carbohydrates, mainly glucose, upon Na+, K(+)-ATPase and lipid peroxidation in rat brain synaptosomal membranes was studied. The membrane damage by irradiated glucose was enhanced in the presence of Fe2+ and was diminished when a free-radical scavenger (BHT) or metal chelators (EDTA, EGTA) were present. It is suggested that a key element in the free-radical membrane damage by irradiated carbohydrates is an Fe(2+)-complex of some species of the radiolysis products. Participation of radiotoxins of carbohydrate origin in radiobiological effects is discussed.

Animals↗
PubMed1992

Sensitivity of the brain synaptosomal membrane Mg(2+)-ATPase activity to arachidonic acid is under control of the Na+,K(+)-ATPase state.

Evidence is presented for the sensitivity of the synaptosomal plasma membrane Mg(2+)-ATPase activity to arachidonic acid being dependent on the functional state of Na+,K(+)-ATPase. An "Inversion effect" was observed at arachidonic acid concentrations exceeding 80 mumol/l when the Mg(2+)-ATPase activity (after ouabain addition) is higher than the total ATPase activity (without ouabain). The "Inversion effect" is reduced by cyclooxygenase inhibitor indomethacin or acetylsalicylic acid and restored by prostaglandin PGA2 or PGD2.

Animals↗
PubMed1991

On the mechanism of shrinkage-induced potassium influx in rat and human erythrocytes.

The rates of 86Rb influx into human and rat erythrocytes were studied in media of various tonicity. At sucrose concentrations below 0.3 mol/l, the ouabain-insensitive, furosemide-inhibited component of influx increased in rat but not in human erythrocytes; this may be explained by a rise in the rate of Na+, K+, Cl-- and/or K+, Cl-cotransport. An increase in osmolarity resulted in a reduction of this as well as of the ouabain and furosemide-insensitive component in rat erythrocytes. At the same conditions a drastic inhibition of Na+, K(+)-pump occurred both in rat and human erythrocytes. We failed to observe a lag-phase in the activation of the cotransport in rat erythrocytes; i. e. the process of activation parallels the shrinkage of cells. In rat erythrocyte ghosts, the shrinkage-induced stimulation of the cotransport was lost, and the direction of their osmotic reaction (inhibition of transport pathways) was similar to that in human erythrocyte ghosts. It is suggested that the mechanism of volume regulation of ion transport in intact cells involves a step of physical amplification via a change in interactions between the protein carcass and the lipid bilayer.

Animals↗
PubMed1991

[The coupling of Na,K-ATPase with the sodium channels in the plasma membranes of the brain synaptosomes of rats].

Effect of neurotoxins veratrine (100 micrograms/ml) and tetrodotoxin (1 microM) on the binding of 3H-ouabain (10(-8) M) with Na,K-ATPase of intact synaptosomes and isolated synaptic membranes was studied. The persistent opening of sodium channels in synaptosomes by veratrine results in an increase of specific binding of the labeled ligand by 20%. A similar effect was caused by Na/H exchanger monensin. Destruction of microtubules with vinblastine and colchicine has no influence on veratrine action, while depolymerization of microfilaments with cytochalasin B reverses the neurotoxin effect. In isolated synaptic membranes veratrine and tetrodotoxin stimulate ouabain binding, the absolute veratrine-induced increment being several times higher in the presence of ATP than in its absence. Since the closed vesicles of any type are not permeable to ATP and ouabain, it means that in the isolated membranes an interaction between sodium channels and Na,K-ATPase molecules takes place. In intact nerve endings such a mechanism may be operative along with the known ways of control of sodium pump and its ouabain-binding site.

Animals↗
PubMed1989

[Calcium transport in brain synaptosomes during depolarization. The role of potential-dependent channels and Na+/Ca2+ metabolism].

The contribution of Ca2+ channels and Na+/Ca2+ exchange to Ca2+ uptake in rat brain synaptosomes upon long- (t greater than or equal to 30 s) and short-term (t less than 30 s) depolarization by high K+ was studied by measuring the 45Ca content and free Ca2+ concentration (from Quin-2 fluorescence). At 37 degrees C, the system responsible for the K+-stimulated uptake of 45Ca (t greater than or equal to 30 s) and the Na+/Ca+ exchanger are characterized by a similar concentration dependence of external Ca2+ (Ca0(2+] and K0+ as well as by an equal sensitivity to verapamil (Ki = approximately 20-40 microM) and La2+ (Ki = approximately 50 microM). These data and the results from predepolarization suggest that the 45Ca entry into synaptosomes at t greater than or equal to 30 s is due to the activation of Na+/Ca+ exchange caused by its electrogenic component, while the insignificant contribution of Ca2+ channels can be accounted for by their inactivation. At low temperatures (2-4 degrees C) which decelerate the inactivation, the initial phase of 45Ca uptake is fully provided for by Ca2+ channels, showing a lower (as compared to the exchanger) affinity for Ca0(2+) (K0.5 greater than 1 mM)m a greater sensitivity to La3+ (Ki = approximately 0.2-0.3 microM) and verapamil (Ki = approximately 2-3 microM); these channels are fully inactivated by predepolarization with K0+, ouabain and batrachotoxin. The Ca2+ channels can be related to T-type channels, since they are not blocked by nicardipine and niphedipine.

Animals↗
PubMed1989

[Cytoskeletal regulation of the sensitivity of brain synaptosomes to the depolarizing action of veratrine].

Using a radioactive permeant cation 3H-tetraphenylphosphonium, the sensitivity of rat brain synaptosomes to depolarizing action of veratrine, which specifically opens the sodium channels, was compared before and after destruction of microtubules and microfilaments. Depolymerization of microtubules with colchicin and vinblastine decreased an apparent affinity of veratrine to its receptor in the channel, while destruction of microfilaments with cytochalasin B had the opposite effect. Colchicine did not change allosteric interactions between the receptor for veratrine and that for scorpion venom in the sodium channel evaluated by the ability of scorpion venom to facilitate veratrine-induced depolarization of synaptosomes. It is suggested that two main cytoskeleton subsystems control the state of sodium channels in the nerve ending.

Animals↗
PubMed1986

Inactivation of muscarinic acetylcholine receptors in brain synaptic membranes by free fatty acids. Evaluation of the role of lipid phase.

Arachidonic, linolenic and linoleic acids decreased the binding of the m-cholinergic antagonist [3H] QNB and did not affect the ratio of high to low affinity binding sites to the agonist carbamoylcholine in rat brain synaptic membranes. In the presence of arachidonic acid, SH-reagent N-ethylmaleimide acquired the ability to block QNB binding to receptor. Lipids in the bilayer and annular regions were probed by fluorescence of 1,6-diphenyl-1, 3, 5-hexatriene and pyrene. A microviscosity drop induced by increasing temperature from 10 to 37 degrees C did not affect the level of QNB equilibrium binding, whereas arachidonic acid strongly inhibited the binding at concentrations inducing the same drop in microviscosity as that induced by heating. For various unsaturated fatty acids an equal extent of receptor blocking was reached at quite different degrees of bilayer fluidization, the state of annular lipid being not changed under these conditions. It is suggested that the effect of unsaturated acids is reached through their direct interaction with the receptor, which undergoes a conformational change, rather than by an alteration of the physical state of the lipid phase of the membrane.

Animals↗
PubMed1983

Effect of tetracaine on veratrine-mediated influx of sodium into rat brain synaptosomes.

Depolarization of synaptosomes with veratrine (0.1 mg/ml) or 50 mmol/l of KCl results in the release of radioactivity from 14C-choline loaded synaptosomes with partial dependence on external Ca2+. Like tetrodotoxin, tetracaine prevented veratrine but not KCl action, with a half-maximal effect at approximately 10(-5) mol/l of anesthetic. A similar half-maximal value was obtained for tetracaine blockade of veratrine-stimulated tetrodotoxin-sensitive 22Na influx into synaptosomes, complete blockage being achieved at 10(-4) mol/l. At this concentration tetracaine failed to modify Ca2+ channels measured by KCl-induced 45Ca uptake. Microviscosity of a lipid bilayer in synaptic membranes evaluated with 5- and 16-doxylstearate spin labels decreased at tetracaine concentrations exceeding 10(-3) mol/l. It is suggested that Na+ channels of synaptosomes are blocked by direct action of anesthetic or through changes in the channel annular lipids.

Acetylcholine↗