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Biomedical subjects

M Thellier

Publications and source records attributed to M Thellier.

At least 55 records · Page 3Linked to original sources
PubMed1985

Voltage Noise in Acer pseudoplatanus Cells : Basic Cellular Noise and Gramicidin a Induced Noise.

The present contribution is devoted to studying the electrical noise of Acer pseudoplatanus cells in culture suspensions. Spontaneous voltage noise of the cells was recorded by means of a microelectrode inserted in the vacuole. The small signal impedance of the cell was measured so that it was possible to study the intensity spectra of the noise. We recorded intensity spectra with cells incubated in 10(-3) molar gramicidin A. Difference spectra showed characteristics of a channel noise. By using the calculated conductance of gramicidin A in an artificial membrane, and by simplifying assumptions for the ionic transports through plasmalemma and tonoplast, we were able to estimate the electrochemical potential difference for K(+) ions across the plasmalemma (3.2 +/- 1 millivolt).

Journal Article↗
PubMed1985

[Compartmental analysis of 6Li/7Li isotope exchange in equilibrium conditions in mouse plasma].

The compartmental analysis of lithium in the mouse plasma has been performed using the stable isotopes, 6Li and 7Li, as tracers. The animals were kept under stationary conditions (concentration of total lithium in plasma maintained equal to 0.28 mM) during the experiment. The isotopic exchange, 6Li/7Li, was described to a good approximation by combining two first-order processes (characteristic parameters: 89 microM and 2.071 X 10(-3) X min-1 for the first one, and 193 microM and 2.215 X 10(-4) X min-1 for the second one). From these kinetic data, it was estimated that the lithium capacities of the plasma and of the cells were 282 and 454 nmol X ml-1, and that the unidirectional fluxes of lithium between plasma and cells and through the kidneys were 0.259 and 0.227 nmol X ml-1 X mn-1. Since the method makes use only of stable, hence harmless, isotopes, one might think of extending it to direct experimentation in man.

Animals↗
PubMed1983

Estimation of local kinetic parameters of exchange of lithium in various substructures of the mouse brain, using the 6Li(n, alpha)3H-nuclear reaction.

The time-constant of lithium (Li)-clearance from the plasma was of the order of 2 hr, while the mean time-constant of lithium-clearance from the bulk of the body cells into the plasma was about 10 times this value. The mean time-constant of lithium ion (Li+)-clearance from various brain substructures (corpus callosum, striatum, hippocampus, neocortex) was comparable to the latter (15-25 hr). Comparison of samples where either a slight diffusion or no diffusion at all had occurred, suggest that between the nerve bodies and the trunks, lithium ions are not uniformly distributed.

Animals↗
PubMed1983

Theoretical analysis of the significance of whether or not enzymes or transport systems in structured media follow Michaelis-Menten kinetics.

Pure Michaelis-Menten enzymes have been studied (i.e., enzymes with a hyperbolic (S, V) behavior in a well-stirred solution). When such enzymes are associated with a structure in vitro, even in the simplest conceivable form (immobilization in a homogeneous gel), they can produce enzymic or transport reactions with many different kinetics (Michaelis-Menten, sigmoidal, dual-phasic, etc.). Therefore, when structured enzyme or transport processes in vivo have sigmoidal kinetics, it is not proof that the corresponding proteins are allosteric. In same manner, when the apparent kinetics are dual-phasic, it is not proof that two enzyme, or transport systems, coexist.

Biological Transport↗
PubMed1981

Compartmental analysis of sulphate transport in Lemna minor L., taking plant growth and sulphate metabolization into consideration.

The compartmental analysis of sulphate transport in cells of Lemna plants has been performed, taking into account the growth of the samples and the metabolization of sulphate into organic thiocompounds during the course of the experiment. The results obtained form efflux and influx experiments are fully consistent with one another. Both unidirectional fluxes between the external medium and the cell wall are very large (order of magnitude of 1 MUMOL/h per g fresh weight of plants). All the other unidirectional fluxes, including the flux of sulphate metabolization, are much smaller (from about 10 to 60 nmol/h per g). Over 70% of the total sulphur of the plant corresponds to that incorporated into organic thio compounds, and over 25% to free sulphate in the vacuola. The pool of free sulphate in the cytoplasm is only about 1% of the total sulphur, and the sulphate content of the cell wall (free spaces) is also about 1%. Two remarks of general relevance have been made concerning the influx curves. First, these curves exhibit a long (several hours), quasi-stationary phase after the first few minutes of absorption, though the slope of this straight line does not correspond to the unidirectional flux of sulphate entry through the plasmalemma (from cell wall to cytoplasm). Second, the Lemna plants seem to be sensitive to the effect of "gas shock'.

Biological Transport↗
PubMed1981

Oscillation of the electrical potential of the frog skin under the effect of Li+: theoretical formulation.

A theoretical model of oscillation is proposed. It is based on the non-linearity introduced in the functioning of the active pump by the presence of lithium. Other plausible causes of oscillation are shown not to interfere in this case. The oscillation is of the local type. Synchronization between the local oscillators is not achieved by diffusional, but by electrical coupling. Numerical calculation shows that the model fits reasonably well to the experimental data.

Animals↗
PubMed1980

Quantitative study of the distribution of lithium in the mouse brain for various doses of lithium given to the animal.

Lithium is detected in the mouse brain with the aid of a (n,alpha) nuclear reaction. The resolving power is of a few micron. The detection efficiency is estimated in a first series of experiments with brain sections of progressively increasing thickness. This allows us to make the microlocation of lithium in the brain sections quantitative. Lithium accumulation in the different brain substructures is then measured for increasing lithium doses given to the animals (1--15 meq/kg animal). For measurements made 6 h after the last injection of lithium, it is corroborated that the accumulation of Li is much larger in the areas with cellular bodies of neurons than in those with nerve trunks only, especially for the smaller doses of lithium given as treatment. Whereas the accumulation curve as a function of the Li concentration of the blood is linear for areas with nerve trunks only, it is negatively bent for the areas with cellular bodies. This and previous data allow us to attempt an estimate of the Li content of the cellular bodies only. A saturation effect seems to appear as soon as the Li concentration in the blood is greater than 1 mM.

Animals↗
PubMed1980

Oscillation of the electric potential of frog skin under the effect of Li+: experimental approach.

When a frog skin is used to separate two compartments, and lithium is added to the external medium, transmembrane electric potential oscillations frequently occur. When no external current is imposed, sustained oscillations, with a period of about 10 min, are maintained for several hours. An oscillation of the Na+ influx accompanies the electric oscillation, though the two oscillations are out of phase to a greater or less extent. Theophyllin promotes a significant decrease in the mean electric potential of the skin, but it does not affect very much the characteristics of the oscillation. Important factors influencing the oscillation are temperature, permeability of the external membrane to lithium, and potassium concentration in the internal medium. No correlation can be detected between oscillation characteristics and skin area. This suggests that the oscillation is of a local nature, possibly originating at the cellular level. Occurrence of macroscopic oscillations implies coupling between local oscillators. Coupling between two epithelia has been studied under diverse conditions. The coupling is of an electrical nature: by varying the value of the coupling resistance, it is possible to control synchronization of the oscillations.

Animals↗
PubMed1980

A tracer method to study unidirectional fluxes of lithium. Application to frog skin.

We describe a new tracer method to measure unidirectional fluxes of Li+ despite the lack of any utilizable radioisotope of lithium. This method uses the purified stable isotopes, 6Li and 7Li, detected with an ion-probe microanalyser. The accuracy is comparable to that obtained for other ions (e.g., Na+) with radiotracers. The method has been applied to frog skin with both faces bathed in a 20% lithium/80% sodium medium. Sodium and lithium unidirectional fluxes have been measured simultaneously. The results are consistent with lithium being actively pumped, the outflux of lithium being, however, much larger than that of sodium.

Animals↗
PubMed1979

Borate Exchanges of Lemna minor L. as Studied with the Help of the Enriched Stable Isotopes and of a (n,alpha) Nuclear Reaction.

Despite the lack of a convenient radioisotope of boron, it is possible to measure unidirectional fluxes of borate between cellular systems and their external medium. It was accomplished by using the two purified stable isotopes ((10)B and (11)B), with (10)B specifically detected by a (n,alpha) nuclear reaction. The method was applied to compartmental analysis of borate with intact plants of Lemna minor L. Four compartments were suggested. Three of them apparently correspond to the three classical ones: free space (including easily dissociable borate monoesters), cytoplasm, and vacuole. The fourth one was interpreted as corresponding to very stable borate diesters in the cell walls. The method allows the determination of the borate capacities of the various compartments and of the borate unidirectional fluxes between the different compartments, at borate flux equilibrium. Other physicochemical data (mono and diester mass action constants, turn over numbers) were evaluated. The results are consistent with what is known of pure substances.

Journal Article↗
PubMed1979

Titration of Isolated Cell Walls of Lemna minor L.

A theoretical model has been built to bypass the equation of titration of the cell wall. This equation, which is an extension of the Henderson-Hasselbach equation, underlines the importance of the exchange constant, the ionic strength as well as the rate of neutralization. The model is restricted to the case when the ionization degree is equal to the neutralization degree. The shape of the titration curve is shown to be strongly dependent on the valency of the base used.Experimental results have shown that isolated cell walls bear at least two kinds of sites. The first sites which are titrated after a short time of equilibration are attributed to polyuronic acids (capacity: 0.3 milliequivalents per gram fresh cell walls). The second sites, are obtained after a long time of equilibration (capacity: 1.2 to 1.3 milliequivalents per gram, fresh cell walls). Titrations have been performed with different bases [KOH, NaOH, and Ca(OH)(2)] and under different ionic strengths.The results obtained with NaOH and KOH do not exhibit any difference of selectivity. Conversely, the sites have a much bigger affinity for the Ca(2+) ions than for the monovalent ones. The apparent pKa of the uronic acids was estimated to lie between 3.0 and 3.4; this is consistent with the values obtained with polyuronic acid solutions.

Journal Article↗
PubMed1978

Exchange Properties of Isolated Cell Walls of Lemna minor L.

From our theoretical treatment which is an extension of the classical Donnan theory, we have estimated the rational selectivity coefficients of the carboxylic groups of the walls during exchanges of divalent ions against monovalent ones (i.e. calcium and potassium or calcium and sodium ions). These coefficients express the interactions between the different ions, those between the counter-ions and the ionized groups of the wall, and the influence of water. These quantitative values are consistent with the great affinity of the carboxylic groups for the calcium ions. They vary with the experimental conditions, showing a purely physicochemical mechanism of "regulation" of the exchanges in the cells walls of Lemna minor L.

Journal Article↗
PubMed1977

[Lithium exchange in from epithelium: determination of unidirectional flux using the stable isotopes 6Li and 7Li in an ionic analyzer].

The use of the stable isotopes 6 and 7 of lithium, and detection with the ionic analyser, allow the measurement of unidirectional transepithelial Li-fluxes, between "external" and "internal" solutions which both contain 80% Na and 20% Li. Efflux was found to be bigger than influx. An important lag-phase on the curve, reveals the interference of a Li-compartment, with a high capacity, in the epithelium itself.

Animals↗
PubMed1976

Detection of stable isotopes of lithium or boron with the help of A (n,alpha) nuclear reaction. Application to the use of 6Li as a tracer for unidirectional flux measurements and to the microlocalization of lithium in animal histologic preparations.

In the particular case of boron and lithium we examine the possibilities of using stable isotopes for experiments of isotopic labelling and microlocalization, as no radioisotopes exist. The detection is made with the help of a specific nuclear reaction, using homogeneous detectors. The first experimental applications are given: transepithelial fluxes of lithium (frog skin) have shown Liefflux values larger than the influx ones. Detailed microlocalization of lithium have been made on histological preparations of mice having received lithium treatment: particularly important contents are found in the hypophysis, the salivary glands, the bladder, the kidney (especially the pelvis), the intestinal system and certain parts of the brain (particularly the hippocampus); the liver, however remains very poor in lithium. Physiological implications are examined.

Animals↗
PubMed1976

[Oscillations in the transepithelial electric potential and current under the influence of lithium].

One can induce sustained oscillations of the spontaneous potential of the frog epithelium by replacing whole or part of the sodium of the external medium with lithium; in the same conditions, the electric current at imposed potential gives damped oscillations. The shape of the oscillations varies much according to the external medium. In the case of the quasi-sinusoidal oscillations, The period is always about 10 mn. We suggest formulating this phenomenon within the framework of the dissipative structurations in non-equilibrium thermodynamics.

Animals↗