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Biomedical subjects

S N Orlov

Publications and source records attributed to S N Orlov.

At least 145 records · Page 8Linked to original sources
PubMed1984

Calcium transport and protein content in cell plasma membranes of spontaneously hypertensive rats.

In the absence of depolarizing agents, 45Ca uptake by synaptosomes of the brain tissue of spontaneously hypertensive rats (SHR) was 40% greater than in normotensive controls. This difference disappeared after membrane treatment with depolarizing agents or with the addition of the Ca channel blocker verapamil. Increased 45Ca uptake was also observed in isolated platelets of SHR. It can be assumed that in both cases these differences were caused by partial depolarization of the plasma membrane as a result of its increased permeability to Na+. The addition of calmodulin to microsomal fractions of SHR brain tissue resulted in a considerably diminished increase in ATP-dependent calcium accumulation. These data are in accord with previous findings obtained in a study on the erythrocyte membrane Ca pump. Data obtained by means of differential scanning microcalorimetry of erythrocyte membranes and gel electrophoresis of membrane proteins indicated a higher band-3 protein content in the erythrocyte membranes of SHR. These data support the concept of primary hypertension as a type of generalized membrane pathology.

Adenosine Triphosphate↗
PubMed1984

[Calcium ion binding in somatic nerves during conduction of rhythmic excitation].

Increase of Ca entry upon excitation depended on stimulation frequency and the types of nerves in crab, frog and squid. The amount of absorbed Ca was high in myelinated nerves whereas the velocity of absorption was higher in nonmyelinated nerves. The maximal level of Ca entry during rhythmic excitation was observed in the frog nerve. The data obtained suggest a mechanism of Ca entry in somatic nerves during rhythmic excitation.

Animals↗
PubMed1984

[Use of 3,3'-dipropylthiodicarbocyanine iodide diS-C3-(5) for the study of conformational changes and detection of Ca-binding proteins].

It was shown that 3,3'-dipropylthiocarbocyanine iodide diS-C3-(5) can be used as a fluorescent probe for registration of conformational changes in calmodulin and troponin C, as well as for determination of concentrations of these Ca-binding proteins in experimental samples. The sensitivity of the method (10(-7) M) is only 5 times less than that of determination of calmodulin by phosphodiesterase and by 1 or 2 orders of magnitude more than that of other techniques based on conformational changes of the protein. The spectral parameters of the fluorescent probe allow to conduct the measurements in turbid media and in the presence of many other optically active substances. Evidence is given testifying the promiscuity of the use of this approach to the study of conformational changes in calmodulin under the action of Ca2+, Mg2+, monovalent cations, temperature and target proteins (troponin I, phosphodiesterase). using phosphodiesterase and Ca-ATPase, it was shown that under certain conditions diS-C3-(5) as well as other amphypathic compounds can modify the activity of calmodulin-dependent enzymes.

Animals↗
PubMed1984

[Intracellular concentration of free calcium in thrombocytes: its characteristics in spontaneous hypertension].

Using the fluorescent Ca-dependent dye quin-2 the authors measured the concentrations of free calcium in the platelet cytoplasm of rats with spontaneous hypertension (SHR) and in normotensive rats (NKWR) serving as control. There were no differences in the baseline levels of free Ca2+ between the platelets of the SHR and NKWR rats. When the cells were loaded with quin-2 in a calcium-free medium and transferred into a medium containing 1 mM of CaCl2, the concentration of Ca2+ in the platelets of the SHR rats became higher. An increase in the content of intracellular Ca2+ induced by thrombin administration was 70% higher in the platelets of the SHR rats as compared with the NKWR rats. The findings obtained suggest that the insufficiency of the Ca-transporting systems of the cellular membranes in primary hypertension described earlier is attended with disturbances in the regulation of the levels of cytoplasm free calcium.

Animals↗
PubMed1984

[Relation between disorders of erythrocyte membrane permeability for monovalent ions and intracellular distribution of calcium in primary arterial hypertension].

The relation of electric potential, lithium and potassium withdrawal rates and erythrocytic balance Na-Na exchange rate constant to intracellular calcium concentration was investigated. Intracellular calcium concentration was modified by means of Ca-ionophore A 23187 and Ca-EGTA buffer. Hypertensive patients showed no differences in erythrocyte membrane electric potential, as determined by chlorine distribution. Only two systems of univalent cations transport were shown to be dependent on the intracellular calcium concentration: calcium increase was accompanied by the opening of K+-channels and the inhibition of erythrocyte membrane Na-K-ATPase. Increased rate of calcium withdrawal from erythrocytes of patients with essential hypertension and spontaneously-hypertensive rats under the effect of Ca-ionophore and moderate Ca2+ concentrations was due to an insufficiency of the cell's Ca-pump rather than disorders in the properties of K+-channels. No significant calcium effect on passive transmembrane ion diffusion, Na, K-cotransport and Na--Na (Na--Li)-countertransport could be demonstrated.

Adult↗
PubMed1984

[Physico-chemical properties of the erythrocyte membranes of normotensive and spontaneously hypertensive rats].

To detect the substrate of molecular alterations in a plasma membrane, found earlier to be typical of chronic hypertension, microcalorimetric study of erythrocyte membranes of spontaneously hypertensive rats was performed. It was found that characteristics of some irreversible therminal transitions in the membranes differ from the corresponding control values. The supposed predominant role of membrane protein denaturation in these transitions is confirmed by the analysis of temperature-dependent infrared spectra, spectra of membrane protein fluorescence and circular dichroism.

Animals↗
PubMed1983

On the interrelation between calmodulin and EGTA in the regulation of the affinity to Ca2+ and the maximal activity of the erythrocyte-membrane calcium pump.

1. Calmodulin distribution in rat erythrocytes and the interrelation between calmodulin and EGTA in regulation of the rate of 45Ca accumulation by erythrocyte-membrane inside-out vesicles were studied. 2. The total content of calmodulin in rat erythrocytes is about 24 mumol/l of cells. About 60% of calmodulin is localized in cytoplasm and 40% (10 mumol/l of cells) of calmodulin is loosely bound to membranes; after subsequent washing by hypotonic solution (membranes A) the content of membrane-bound calmodulin decreases up to 0.1 mumol/l of cells. 3. The addition of exogenous calmodulin to membranes A results in increase of the maximal activity of the Ca-pump and does not influence its affinity to Ca2+. Troponin I (30 microM) completely abolishes the calmodulin effect on the Ca-pump activity without significant alterations in its basal activity. 4. The addition of EGTA in the membrane-washing solution results in decrease of the membrane-found pool calmodulin up to 0.01 mumol/l of cells (membranes B). This procedure is accompanied by decrease of the affinity of Ca-pump to Ca2+ and does not influence its maximal rate. 5. The effect of EGTA treatment (membranes B) on the affinity of Ca-pump to Ca is abolished after addition of micromolar concentrations of calmodulin or millimolar concentration of EGTA in the incubation medium. The increase of EGTA concentration in the incubation medium results in decrease of the affinity of Ca-pump to calmodulin. 6. It is assumed that two essentially different pools of calmodulin participate in the regulation of the activity of Ca-pump. (a) The pool of calmodulin which is loosely bound to membrane (this size is dependent on calmodulin concentration in cytoplasm) determines the maximal activity of Ca-pump. The effect of this calmodulin pool is blocked by troponin I. (b) The tightly bound pool of calmodulin which is removed by EGTA treatment determines the affinity of Ca-pump to Ca. 7. In this connection the reasons for contradictory data on estimation of calmodulin effect on the kinetic parameters of plasma membrane Ca-pump are discussed.

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↗
PubMed1983

Calmodulin-dependent Ca2+ transport in erythrocytes of spontaneously hypertensive rats.

Ca2+ transport in inside-out vesicles of the erythrocyte membranes of spontaneously hypertensive rats (SHR) was studied. In the presence of calmodulin, the rate of 45Ca uptake by the erythrocyte membranes of SHR was half that of erythrocyte membranes of the normotensive control group. It is suggested that the decrease of the rate of calmodulin-dependent calcium transport across the plasma membrane may be a cause for the increased intracellular calcium content found in some tissues of spontaneously hypertensive rats in previous studies.

Animals↗
PubMed1983

Calcium transport in synaptosomes and subcellular membrane fractions of brain tissue in spontaneously hypertensive rats.

The uptake of Na+ and Ca2+ by synaptosomes and uptake of Ca2+ by the mitochondria and microsomes of brain tissue of rats with spontaneous hypertension (SH rats) and normotensive Kyoto-Wistar rats (WKY rats) were studied with an isotope-exchange method. By means of inhibitor analysis it has been shown that calcium influx into the synaptosomes during depolarization of their plasma membrane takes place only through the potential-dependent channels in both groups of animals. Basal Ca2+ uptake by the synaptosomes of hypertensive rats was increased, apparently by partial depolarization of the synaptosome membrane caused by the increased membrane permeability to Na+ (basal Na+ uptake by synaptosomes was found to be increased in hypertensive rats). Ca2+ uptake by mitochondria of hypertensive rats was increased, and the Ca2+ uptake by microsomes was decreased in these rats compared with controls. The increment of the maximal Ca2+ transport rate in microsomes after the addition of calmodulin was decreased in spontaneously hypertensive rats compared with normotensive animals. Thus alterations in the interaction of calmodulin with the Ca2+-transporting systems of the plasma membrane are an important part of the widespread membrane defect observed in spontaneous hypertension.

Animals↗
PubMed1983

[Mechanisms of calcium transport in brain synaptosomes as affected by depolarization].

Data of the inhibitory analysis suggest that the increase in the content of calcium in veratrine-, ouabain- and 80 mM K+-depolarized synaptosomes is due to Ca2+ influx through the potential-dependent calcium channels. The decrease of the intracellular concentration of Ca2+ in depolarized nerve endings is mainly caused by the calmodulin-dependent Ca,Mg-ATPase of synaptolemma and mitochondria. The regularities of ATP-dependent Ca2+ transport in synaptosomal plasma membranes were studied on the microsomes whose properties were found identical to those of native synaptolemma. A comparison of the kinetic parameters of Ca-transport systems in brain microsomes and mitochondria and the data on extensive inhibition of 45Ca uptake by rotenone and oligomycin suggest that mitochondria play a key role in the control of intraterminal concentration of Ca2+ during nerve impulse conduction.

Animals↗
PubMed1983

[Aggregation, membrane potential and Na+ and Ca2+ in the thrombocytes of rats with spontaneous hypertension].

Platelet aggregation, plasmatic membrane potential and sodium and calcium uptake were investigated in spontaneously hypertensive rats (SHR). The sensitivity of SHR's platelets to effects of all aggregational agents examined (ADP, collagen, ADP + noradrenaline) was enhanced. Ca-ionophore A 23187 caused complete SHR platelet aggregation when Ca2+ concentration in the incubation medium was 20-30% below the level of normotensive control specimens. The membrane potential of SHR platelets was reduced by 8-12 mV, which may be attributed to increased content of metabolizing sodium as well as a higher rate of its transmembrane exchange. A higher rate of Ca2+ uptake by SHR platelets may be related to partial depolarization of the membrane and the cation's diffusion along potential-dependent Ca-channels.

Adenosine Diphosphate↗
PubMed1983

[Participation of calmodulin in the regulation of plasma membrane electric potential by intracellular calcium].

The effect of Ca2+ on the electric potential and permeability of human erythrocyte membranes for K+ was investigated. An increase of K+ concentration in a medium containing a Ca-ionophore A 23187 causes hyperpolarization of the erythrocyte membrane (by 50-60 mV) due to a 70-fold increase of its permeability for K+ (K0.5 for Ca2+ in both cases is equal to 2-3 microM). Using calmodulin-deficient inside-out erythrocyte membrane vesicles, it was demonstrated that regulation of the transmembrane potentials by Ca2+ is mediated by its interaction with calmodulin (K0.5 for Ca2+ and calmodulin is equal to 2-3 microM and 100-150 nM, respectively). It was assumed that the Ca2+-calmodulin complex is involved in the functioning of the plasma membrane K+-channel.

Calcimycin↗
PubMed1983

Calmodulin-dependent Ca2+ transport across plasma membranes in primary hypertension.

The rate of calcium transport in the erythrocytes in both forms of primary hypertension [essential hypertension (EH) of humans and spontaneously hypertensive rats (SHR)] and in microsomes of SHR brain were studied. In the erythrocyte membranes subjected to calmodulin depletion by EGTA treatment both the affinity of the Ca-pump for Ca2+ and its maximal activity in primary hypertension did not differ from normotensive controls. The addition of exogenous calmodulin to calmodulin-stripped membranes from erythrocytes of EH or SHR and microsomes of SHR brain resulted in a smaller increase of the Ca-pump activity. It is suggested that the decrease of the rate of calmodulin-dependent calcium transport across the plasma membrane may be a cause for the increased intracellular calcium content found in some tissues in primary hypertension.

Animals↗
PubMed1983

[Microcalorimetric study of erythrocyte membrane suspensions in normal subjects and in hypertension].

Microcalorimetric method was used to study the temperature dependence of thermal absorption of human red cell membrane suspension in health and essential hypertension. In disease, the temperature dependence of individual irreversible thermoinduced transitions characteristic for human red cell membranes was appreciably changed, which was comparable with disorders of protein-lipid interactions discovered before by fluorescent examination, while elevated enthalpy of one of the transitions pointed to the possibility of enriching these membranes with band 3 protein. Unlike normal, red cell membranes in essential hypertension exhibited a special thermoinduced irreversible transition with the thermoabsorption maximum about 41 degrees C.

Adult↗
PubMed1983

[Differences in the rates of Na/Li-countertransport in the erythrocyte membranes of hypertensive and renal hypertensive patients].

Erythrocyte membrane permeability was studied by means of sodium-lithium countertransport measurement in patients with essential and renal hypertension and in healthy volunteers. In essential hypertension, erythrocyte membrane permeability was 60 per cent higher than the control value. There was no difference between permeability values of renal hypertensive patients and healthy subjects. Erythrocyte membrane permeability was not related to age or sex in normotensive subjects. Permeability pattern is assumed to be a useful parameter for differential diagnosis of arterial hypertensions and for establishing hereditary origin of essential hypertension.

Adult↗