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Biomedical subjects

V Vasilescu

Publications and source records attributed to V Vasilescu.

At least 19 recordsLinked to original sources
PubMed1987

Sequential sodium-proton exchange in thrombin-induced human platelets.

Thrombin stimulation of human platelets initiates a membrane depolarization attributable to a Na+ influx into, and an alkalinization of, the cytoplasm, both of which follow a similar rapid time scale and thrombin-dose dependence. These responses precede secretion of the contents of the dense granules (serotonin) and, after 1 minute, of lysosomes (beta-glucuronidase). We have evaluated these parameters in the presence of 2H2O in order to determine if the Na+ influx and H+ efflux are sequential or simultaneous. NMR evidence indicates that 2H2O equilibration in rapid, and virtually complete within the 3 min prestimulation platelet equilibration period. In response to an 0.05 U/ml addition of thrombin, the rate of depolarization is 70-80% slower in 2H2O than in H2O. The time to reach maximal depolarization is 5 to 10 seconds longer in 2H2O, the extent of depolarization 60% inhibited, and the pH change 85% inhibited. The serotonin secretion is unaltered, while the beta-glucuronidase secretion is 130-180% enhanced. Dimethylamiloride inhibits the Na+ influx and the pH change completely. These results suggest that the Na+ and H+ fluxes across the plasma membrane are interdependent but neither simultaneous nor electroneutral. Furthermore, granule secretion, previously shown by us to be independent of the existent Na+ gradient, depends on the cytoplasmic K+ and H+ concentrations.

Amiloride↗
PubMed1986

On the electrical conductivity of rhodopsin solutions.

Measurements were made on the conductivity of digitonin extracts of frog rhodopsin with and without previous light exposure. The light-dark difference in conductivity is observed at low concentrations of rhodopsin and detergent.

Animals↗
PubMed1986

Structure/nerve membrane effect relationships of some local anaesthetics.

Data on electron structure and octanol-water partition coefficients of certain local anaesthetics are compared with the capacity of reversibly block the action potential of the frog sciatic nerve. Some active parts in the molecules of these substances have been shown to be primarily involved in the action of local anaesthetics.

Action Potentials↗
PubMed1982

Water involvement in the mechanisms of retina electrical activity.

Retina is an excitable system containing approximately 90% water. As we found that deuteration selectively changes amplitudes and latencies of retina biopotentials, specifically the ON and OFF responses, we used it to probe the role of water in those processes. A study of the retina deuteration kinetics was simultaneously performed. This revealed the existence of at least two retinal water compartments. The data suggested a third compartment also, with a lower motional "degree of freedom," existing where H2O-D2O exchange becomes important only after saturation by D2O of the first two compartments. Correlation of the electrophysiological effects of D2O with the kinetic data suggests that the ON response is related to the first water compartment and the OFF response to the third. The results point to independence on the ON and OFF response mechanisms and, very probably, to their different morphological origins.

Animals↗
PubMed1981

Computer simulation of the effect of the nodal gap resistance on ionic current measurements in the Ranvier node membrane.

Results are presented of a computer simulation of the effect of the irreducible resistance introduced by the nodal gap, in series with the impedance of the axon membrane. A clamp potential is applied to a structure modeled as an electric circuit composed of a resistance in series with the membrane impedance, and modified nerve equations describing membrane currents are solved to predict the effect of nodal series resistance on these currents. These studies reveal changes in the absolute values and kinetics of the ionic currents (errors greater than 10-20%) for selected values of series resistance.

Animals↗
PubMed1979

Water compartments in living, glycerinated and fixed skeletal muscles of the frog.

The kinetics of water replacement with heavy water (deuterium oxide) in the gastrocnemius and sartorius muscles of the frog under isotonic conditions, studied both gravimetrically and by infrared photometry, reveals three water compartments: (i) non-exchangeable (approximately 80 ml/kg fresh weight), (ii) slowly exchanging (approximately 500 ml/kg fresh weight), (iii) rapid exchanging--extracellular (approximately 200 ml/kg fresh weight). Exposure to both glycerol and glutaraldehyde increases the permeability coefficients and the amount of rapid exchanging water; glutaraldehyde also increases the amount of non-exchangeable water. Approximately 90% of the water is kept in the tissue only by weak intermolecular forces, the energies of which amount to 1 kcal/mol. The amount of non-exchangeable water is equivalent to about six continuous adsorption layers covering the myofilaments. Approximately 70% of the tissue water appears to be replaced by glutaraldehyde during standard fixation.

Aldehydes↗
PubMed1978

Water compartments in the myelinated nerve. III. Pulsed NMR results.

3 experimentally distinct transverse relaxation components of the water in frog sciatic nerve are obtained by Carr-Purcell-Meiboom-Gill technique. The relative weights of these components: approximately 29%; approximately 50%; approximately 21% fit well with water compartments in this tissue as revealed by previous methods.

Animals↗
PubMed1975

Contributions to the perfecting of the enzymatic method used for the determination of ATP in biological systems.

The improvement of methods for the determination of ATP, that is the increasing of their sensitivity is extremely useful for the study of excitation-energy coupling in excitable membranes. Such investigations from the object of the present work in which there is proved that the microanalytical method for the dosing of ATP, based on the enzymatic reaction with luciferin-luciferase system, may be converted into a ultramicroanalytical method and therefore used also in other fields of research, as for example the ATP biosynthesis in cell cultures.

Adenosine Triphosphate↗