PubMed Health⌕ Search

Biomedical subjects

A Kövér

Publications and source records attributed to A Kövér.

18 recordsLinked to original sources
PubMed2005

Energy-sharing asymmetries in ionization by positron impact.

The triply differential cross section of molecular hydrogen for ionization by 50 eV positrons has been determined, for the first time, for both the ejected electron in coincidence with the remnant ion and for the scattered projectile. Asymmetries in the energy sharing between the two light particles in the final state are observed, with the electron spectrum being shifted to significantly lower (and the scattered positron to correspondingly higher) energies than expected. A similar shape is observed in the case of the ejected electron spectrum from a helium target at the same excess energy.

Journal Article↗
PubMed1999

The importance of bioimpedance (BIA) analysis and Cardio Tens (24-h ABPM and ECG) monitoring in the dialysis programme.

The authors performed bioimpedance analysis and Cardio Tens (24-h ABPM and ECG) monitoring in 66 patients (28 males, 38 females) treated in the chronic haemodialysis programme. They investigated the correlations between the body weights before, during and after dialysis, the changes of the water compartments and fat body weight, and the recorded values of blood pressure and ECG alterations. On the basis of the measurements by this non-invasive method it is concluded that, as a result of dialysis and ultrafiltration, the total body weight and total body water are decreasing in a greater extent in men than in women. By gradually decreasing the body weight, the optimal dry weight could be attained, which resulted in the reduction of blood pressure or even normotension. In the course of dialysis the values of bioimpedance and bioreactance increase. The intradialytic hypotensive indispositions were accompanied by a significant reduction of bioreactance (n = 16). The BMI, total body weight and total body water hyperlipidaemic, hypalbuminic patients with treatment-resistant hypertension are considerably larger than those of the patients with normal blood pressure (p<0.01). During Cardio Tens monitoring 53% of the patients proved to be dippers, 47% of whom had ST depression, while in 73% of the non-dippers ischaemic alterations were encountered together with high hyperbaric impact values. The total body weights and total water compartments of patients returning to dialysis with an excess body weight of more than 3.5 kg were significantly larger than of patients who were cooperative and had no oedemas. In the last hour of dialysis and during the following few hours, arrhythmias and ST depressions of the cardiovascularly instable patients appeared more frequently. The total water compartments of these patients are significantly larger than normotensive, normolipaemic patients with appropriate serum albumin concentrations. The importance of the BIA and Cardio Tens monitoring in determining the optimal dry body weight and improving the cardiovascular condition of the patients is emphasized.

Aged↗
PubMed1995

Characteristics of stretch-release induced tension development in arterial smooth muscle.

Stretching helical strips of porcine a. carotis comm. to 1.7 times the resting length increases myosin light chain phosphorylation from 0.22 to 0.67 mol phosphate/mol light chain. While stretch is maintained, the stretch induced light chain phosphorylation decreases and reaches the resting level over a period of 60 minutes. The fully stretched arterial strips containing maximally phosphorylated myosin light chain cannot generate active tension which indicates, according to the sliding filament theory, the lack of overlap between actin and myosin filaments. When stretch is released from these muscle strips active tension develops. The amplitude of this stretch-release induced tension depends on the level of myosin light chain phosphorylation related to the time interval between stretch and release as well as on the extent of the overlap zone related to the length of the released strip. Three-dimensional graphic representation of both measured and interpolated data points in an active tension-light chain phosphorylation-muscle length space reveals a contractility surface which demonstrates that active tension appears as a sigmoidal function of light chain phosphorylation, on the one hand and shows maximum as a function of muscle length, on the other hand.

Animals↗
PubMed1990

New approach of three-dimensional crystallization of the Ca(2+)-ATPase of sarcoplasmic reticulum.

Selective extraction procedure was applied for obtaining different proteins from sarcoplasmic reticulum vesicles following the main steps of previous observations. High concentration of a nonionic detergent, such as polyoxyethylene-10-lauryl ether (C12E10) prevented the formation of Ca(2+)-ATPase crystals. It has been observed that only the 300 kDa protein could induce crystallization from among proteins being undissolved from of membrane. A modification of MacLennan's procedure--applied for ATPase precipitation from deoxycholate solubilized sarcoplasmic reticulum--has been described and an ammonium acetate precipitated Ca(2+)-ATPase was used in the experiments for increase of Ca(2+)-ATPase concentration in the crystallization process. The repeated supplementation of purified and C12E10 solubilized Ca(2+)-ATPase with ammonium acetate precipitated Ca(2+)-ATPase made possible a formation of larger and larger crystals with different periodicity.

Animals↗
PubMed1988

Changes of calcium compartmentalization of skeletal muscle under ionic and drug influence.

Compartmentalization of calcium was studied in frog semitendinosus using 45Ca radioisotope under exchange diffusion condition. Computer based deconvolution was employed to determine the "volume" and the apparent binding constant of the resolved six components. Assuming kinetically parallel and independent compartments nickel treatment slows down the calcium movement through the sarcoplasmic reticulum membrane and for the calcium ions causes competition of the membrane of transverse tubuli and of the sarcoplasmic reticulum. Veratrine treatment caused different effect in the presence and in the absence of sodium ions, demonstrating the essential role of Na+ in equilibrium with Ca2+ exchange processes/ATPases in the Ca2+ uptake and release by sarcoplasmic reticulum. Effect of caffeine and Dantrolene basically opposite on the compartment corresponds to the sarcoplasmic reticulum and similar on the transverse tubuli in term of speed of exchange diffusion.

Animals↗
PubMed1988

Effect of sodium-ascorbate and vanadate on the Rb+-uptake of human red blood cells.

To follow the Rb+-uptake of human red blood cells (rbc-s) under different circumstances, a micro-method was developed. According to our experiments the Rb+-uptake of rbc-s in a healthy person was about 3.5-4.0 mumoles Rb/mg Fe at 37 degrees C during 120 minutes. When red cells were incubated with solutions containing different concentrations, between 15 and 120 mmole/l, of Na-ascorbate [Na-ascorbate was applied at the expense of Na-isethionate (sodium salt of 2-hydroxyethan-1-sulfonic acid)] the Rb+-uptake of red cells increased at 37 degrees C with 37 to 70% respectively. In other experiments it was established that the ouabain-sensitive Rb+-uptake of rbc-s decreased with 50% in the presence of 0.1 mmole/l vanadate, while if Na-ascorbate was applied simultaneously with different concentrations of vanadate, or after a preincubation with 1 mmole/l vanadate, the Rb+-uptake of red cells, which had been reduced by vanadate, returned close to that of control. This effect can be explained by the reductive property of Na-ascorbate, i.e. by the transformation of vanadate to vanadil.

Ascorbic Acid↗
PubMed1986

Myotonic responses produced by alteration of the function of ionic channels.

It has been established that in sodium isethionate Ringer's solution containing chloride ions at low concentration (0-6.1 mmol/l) a repetitive firing of action potentials (APs) could be induced systematically by stimulation of muscle fibres with single square impulses. Repetitive firings occurred also on slow depolarization elicited by different agents e.g. by some antibiotics (primycin, desertomycin) which block potassium channels, or aldehydes (acrolein). On the basis of own and literary data it is concluded that under physiological conditions a high chloride concentration in the extracellular space prevents the occurrence of repetitive firing of APs which would result from the depolarization of tubular membrane on potassium ion accumulation in the luminal fluid of T-tubules.

Acrolein↗
PubMed1986

Discoupling of excitation-contraction processes by urea treatment of frog skeletal muscle.

On exposure (E) of frog semitendinosus muscle to 400 mmol/l urea (U) in sodium chloride Ringer's solution, the tension development to isoK+ solutions decreased, while in choline chloride Ringer it increased. On quick removal (R) of urea, always a block of excitation-contraction (E-C) coupling occurred accompanied by transient or persistent swelling of fibres and a similar but definite decrease of their resting membrane potential (Fig. 2). Muscle contraction could be elicited by caffeine even after UER-treatment but then only the slow tension increase (second phase of normal caffeine contraction) occurred (Fig. 3a). The fast tension increase to caffeine (first phase) could be restored if after UER-treatment 5 mmol/l mannitol (Fig. 3b), a 20 min treatment with choline chloride (Fig. 4a) or sodium isethionate (Fig. 4b) Ringer's solution of double osmolarity were applied. Caffeine contraction could not be elicited when sodium chloride Ringer's solution of double osmolarity was used under similar conditions (Fig. 5). E-C block to isoK+ solution persisted in all these experiments. E-C coupling could partially be restored by short treatment of muscle with caffeine (Figs 6a, b).

Animals↗
PubMed1985

Intracellular hydrolysis of EGTA-esters.

It has been established that the hydrolysis of EGTA-acetoxymethylester (AME) by red blood cells is about the tenth of the hydrolysis of acetylthiocholine (Ac-S-Ch). This splitting of AME could be inhibited by about 50% by prostigmine at a concentration of 0.75 X 10(-5) mol/l, while the splitting of Ac-S-Ch was totally inhibited by the same prostigmine concentration. The hydrolysis of AME by the so-called white-ghost preparation was considerably inhibited by prostigmine (KI = 5 X 10(-8) mol/l), and this inhibition proved to be a competitive one. The splitting of AME by membrane-free cytosol fraction could not be inhibited by prostigmine. Human red blood cells do not hydrolyse EGTA-ethylester (EE). This compound decomposes spontaneously at room-temperature, its reaction-product formed in the Hestrin-reaction is unstable, the developed colour gradually turns pale. On the other hand, AME does not hydrolyse spontaneously at room-temperature and the colour-intensity of its Hestrin-reaction does not decrease with time. Using chelator-and dye-indicator esters to reach different concentrations of free chelators and dye-indicators intracellulary (IC), the extracellular hydrolysis of esters has to be taken into account or this external breakdown has to be inhibited.

Acetylthiocholine↗
PubMed1980

Effect of primycin on some electric properties of the frog skeletal muscle.

The effect of primycin, a guanidine-type antibiotic was studied on the electric properties and 42K+ uptake of the frog sartorius and semitendinosus muscle. Both in normal and choline chloride Ringer solution, primycin evoked a concentration and time dependent depolarization of the surface membrane of the muscle. This depolarization was significantly increased by Na ions. Primycin treatment was shown to evoke a dose-dependent decrease of the depolarization induced by 20 mM K+-Ringer. When the muscles were incubated in a Ringer solution containing choline chloride, during an incubation period of 30 min the uptake of 42K+ was decreased to 12% upon the exposure to 5 x 10(-6) mol primycin as compared to the control value. As the primycin-induced depolarization increased, the shape and amplitude of the action potentials elicited by square-wave electric impulses were altered and decreased, respectively. In sodium isaethionate Ringer 1--2 x 10(-6) M primycin induced a slow depolarization resulting in firing potentials. The results suggest that primycin depolarizes the surface membrane exclusively through the blockade of the resting K+ channels, the other phenomena being the results of this depolarizing effect.

Action Potentials↗
PubMed1976

The effect of La3+ on the characteristics of fragmented sarcoplasmic reticulum.

Fragmented sarcoplasmic reticulum (FSR) was prepared from the white muscles of the catfish (Amiurus nebulosus). The effect of La3+ on the functional characteristics of FSR was studied. La3+ in a concentration higher than 10(-4) M was found to decrease or arrest Ca2+ accumulation, cholinesterase activity and the activation of ATPase by Ca2+. La3+ added after the elimination of membrane-bound Ca2+ of FSR (1 mM EGTA, pH 7.1) does not substitute Ca2+ in its functions. The cholinesterase activity of FSR solubilized by deoxycholate and purified by gelfiltration is inhibited by La3+ present in a concentration higher than 10(-4) M and simultaneously with inhibition, the absorbance at 280 nm is increased. Ca2+ gives rise to similar changes only in concentrations higher than 10(-2) M.

Animals↗