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PubMed1976

[Effects of Bunaphtine on right atrial and ventricular monophasic action potentials in man. Preliminary note (author's transl)].

Effects of Bunaphtine on right atrial and ventricular monophasic action potentials were investigated in 6 patients using the technique of endocavitary recording with a suction electrode. The authors found that the drug, given intravenously in the usual therapeutic dosages, increases the total duration of MAP both atrial and ventricular, together with quite a proportional ERP prolongation. At ventricular level MAP's increase in correlated to a prevailing and strong increase of phase 3. However, the variations of the MAP's amplitude, its O dv/dt phase and the cardiac specific conduction's alterations (noted only at higher dosages) have been inconstant and poor on the whole. On the basis of these results, the mechanism of the action of the drug is discussed.

Action Potentials↗
PubMed2004

Separation of basic compounds by capillary electrochromatography on an X-Terra RP18 stationary phase.

In this work we demonstrate that the X-Terra RP18 stationary phase, specially designed for the analysis of basic compounds in liquid chromatography, may be successfully used in capillary electrochromatography. Although this packing material does not afford a sufficient electroosmotic flow with classical hydro-organic mobile phases, the addition of a surfactant that adsorbs onto the stationary phase allows to generate a sustainable electroosmosis flow (EOF), the direction of which depends on the charge of the surfactant. The way of manipulating the electroosmotic flow is described (nature and concentration of the added surfactant, proportion of the organic modifier in the mobile phase, pH). It is then demonstrated that high efficiencies can be reached with this packing material (up to 220,000 plates/m with a mean diameter particles of 3.5 microm) when it is operated at high linear velocities. Then the separations of different classes of compounds such as amphenicol antibiotics, macrolide antibiotics or basic test solutes with mobile phases with pH up to 10.8 are described. The influence of the addition of sodium dodcylsulfate (SDS) to the mobile phase on the retention is described and the selectivity of the X-Terra RP18 stationary phase is compared to that of a more traditional phase, i.e. Hypersil C18 stationary phase with SDS added to the mobile phase. However, it is shown that a good repeatability of the retention factors can only be obtained when the ionization of the compounds is totally suppressed since electrolysis of the buffered hydro-organic mobile phase occurs in the buffer reservoirs leading to a variation of the mobile phase pH and consequently to a modification of the ionization degree of the solutes having their pKa close to the mobile phase pH.

Anti-Bacterial Agents↗
PubMed2004

Thermodynamic nonequilibrium phase change behavior and thermal properties of biological solutions for cryobiology applications.

Understanding the phase change behavior of biomaterials during freezing/thawing including their thermal properties at low temperatures is essential to design and improve cryobiology applications such as cryopreservation and cryosurgery. However, knowledge of phase change behavior and thermal properties of various biomaterials is still incomplete, especially at cryogenic temperatures (< or = -40 degrees C). Moreover, in these applications, chemicals are often added to improve their outcome, which can result in significant variation in the phase change behavior and thermal properties from those of the original biomaterials. These chemical additives include cryoprotective agents (CPAs), antifreeze protein (AFP), or cryosurgical adjuvants like sodium chloride (NaCl). In the present study, phase change behavior and thermal properties of saline solutions--either water-NaCl or phosphate buffered saline (PBS)--with various chemical additives were investigated. The chemical additives studied are glycerol and raffinose as CPAs, an AFP (Type III, molecular weight = 6500), and NaCl as a cryosurgical adjuvant. The phase change behavior was investigated using a differential scanning calorimeter (DSC) and a cryomicroscope. The specific and latent heat of these solutions were also measured with the DSC. The saline solutions have two distinct phase changes--water/ice and eutectic phase changes. During freezing, eutectic solidification of both water-NaCl and PBS are significantly supercooled below their thermodynamic equilibrium eutectic temperatures. However, their melting temperatures are close to thermodynamic equilibrium during thawing. These eutectic phase changes disappear when even a small amount (0.1 M glycerol) of CPA was added, but they are still observed after the addition of an AFP. The specific heats of these solutions are close to that of ice at very low temperatures (< or = -100 degrees C) regardless of the additives, but they increase between -100 degrees C and -30 degrees C with the addition of CPAs. The amount of latent heat, which is evaluated with sample weight, generally decreases with the addition of the additives, but can be normalized to approximately 300 J/g based on the weight of water which participates in the phase change. This illustrates that thermal properties, especially latent heat, of a biomaterial should be evaluated based on the understanding of its phase change behavior. The results of the present study are discussed in the context of the implications for cryobiology applications.

Biomimetic Materials↗
PubMed1975

Optokinetic nystagmus during selective retinal stimulation.

Nystagmic eye movements in response to selective optokinetic stimulation of different parts of the retina were studied in normal human subjects by two methods: 1. a digital computer controlled by the eye movement signal was used to generate an optokinetic display which stimulated only the peripheral retina, simulating a central scotoma, and 2. a single dot of 0.6 degrees in diameter was used as the stimulus during maintained forward gaze. The results show that stimulation of the central or peripheral retina alone can produce optokinetic nystagmus in man, and that essentially the same type of nystagmus is produced in both cases. The slow phase velocity of nystagmus evoked from the peripheral retina falls off rapidly with distance from the fovea but can be facilitated by attention. Results are compared with other findings and a possible explanation is offered for the observed variation in slow phase speed which occurs during constant velocity optokinetic stimulation.

Adolescent↗
PubMed1994

Partial visual feedback and spatial end-point accuracy of discrete aiming movements.

Five experiments are reported in which the effect of partial visual feedback on the accuracy of discrete target aiming was investigated. Visual feedback was manipulated through a spectacle-mounted liquid-crystal tachistoscope. The length of the visual feedback interval was varied as a percentage of the instructed movement time. In Experiment 1, the length of the vision interval was manipulated symmetrically at the beginning- and end-phase of the movement, whereas in the remaining experiments, the vision time was varied with respect to the end-phase only. The variations at the end were examined for different distances (Experiment 2), different movement speeds at the same distance (Experiment 3), and in small interstep intervals (Experiment 4). A vision time of more than 150 ms at the end-phase of the movement enhanced aiming performance in all experiments. Longer vision times monotonously improved aiming accuracy; the fifth experiment showed that a vision time of about 275 ms was sufficient for near-perfect aiming. Furthermore, the significance of vision during the first phase of a movement was demonstrated again. The results of the five experiments pointed to shorter visuomotor processing times. To explain the beneficial effects of short vision times for aiming accuracy, we propose a model of visuomotor processing that is based on the stochastic optimized submovement model of Meyer, Abrams, Kornblum, Wright, and Smith (1988).

Journal Article↗
PubMed2006

Ground and excited states of spinor fermi gases in tight waveguides and the Lieb-Liniger-Heisenberg model.

The ground and excited states of a one-dimensional (1D) spin-1/2 Fermi gas (SFG) with both attractive zero-range odd-wave interactions and repulsive zero-range even-wave interactions are mapped exactly to a 1D Lieb-Liniger-Heisenberg (LLH) model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, such that the complete SFG and LLH energy spectra are identical. The ground state in the ferromagnetic phase is given exactly by the Lieb-Liniger (LL) Bethe ansatz, and that in the antiferromagnetic phase by a variational method combining Bethe ansatz solutions of the LL and 1D Heisenberg models. There are excitation branches corresponding to LL type I and II phonons and spin waves, the latter behaving quadratically for small wave numbers in the ferromagnetic phase and linearly in the antiferromagnetic phase.

Journal Article↗
PubMed1984

Model of gradual phase shift of theta rhythm in the rat.

CA1 pyramidal cell is modeled by a linked series of passive compartments representing the soma and different parts of the dendritic tree. Intracellular postsynaptic potentials are simulated by conductance changes at one or more compartments. By assuming an infinite homogeneous extracellular medium and a particular geometrical arrangement of pyramidal cells, field potential profiles are generated from the current source-sinks of the compartments. The pyramidal cells are driven at the theta (theta)-frequency at different sites of the dendritic tree in order to simulate external driving of hippocampus by the septal cells. Inhibitory or excitatory driving at different sites gives extracellular dipole fields of different null zones and maxima. Phase reversal (180 degrees) of a dipole field generated by synchronous synaptic currents is completed within a depth of 150 micron. By driving two spatially distinct but overlapping dipole fields slightly phase-shifted (30-90 degrees) from each other, the resultant field shows a gradual phase shift of 180 degrees in over 400 micron depth and no (stationary) null zones. The latter field correspond to the theta-profiles seen in the freely moving rat. Somatic inhibition is proposed to be the synaptic process generating the theta-field potentials (named dipole I) in the urethananesthetized or curarized rat. Dipole I has amplitude maxima at the basal dendritic and the distal apical dendritic layers, with a distinct null zone and phase reversal at the apical side of the CA1 pyramidal cell layer. Rhythmic distal dendritic excitation, time-delayed to somatic inhibition, is proposed to be the additional dipole (dipole II) found in freely moving rats. The combination of dipoles I and II, phase-shifted from each other, causes the gradual theta-field phase shift. Experimental studies indicate that dipole I is atropine-sensitive and probably driven by a cholinergic septohippocampal input, whereas dipole II is atropine-resistant and may come from a pathway through both the septum and the entorhinal cortex. Variations of the phase profiles of the theta-field in freely moving rats by administration of anesthetic and cholinergic drugs and by normal changes in theta-frequency could be accounted for by the proposed model. Changes of the intracellular membrane potential, cellular firing rate, and evoked excitability at different phases of the theta-rhythm in anesthetized and freely moving rats can be predicted from the model, and they are in general agreement with the extant literature. In conclusion, theta-field is generated by a rhythmic somatic inhibition phase-shifted with a distal apical-dendritic excitation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

The effect of phase differences on the time-dependent variation of the zeta potential of hydroxyapatite.

The osteoconductive nature of calcium phosphate ceramics (CPC) follows from several proven effects, such as a direct bone attachment and enhanced bone tissue formation. Mechanisms leading to these phenomena are still largely undiscovered. Specifically, little is known about the CPC surface and cell-driven reactions. These atomic and molecular level events are involved in tissue attachment and enhanced tissue formation. It is hypothesized that the zeta potential of these ceramics is directly related to the surface reactivity governing osteoconductivity. As a first step in our analysis, the zeta potential of stoichiometric and Ca-deficient hydroxyapatite was determined as a function of immersion time. It is concluded that, under the conditions of the experiment, the observations support the hypothesis in a dual way. First, the absolute values of the zeta potential which were measured are related to electrokinetic potentials known to cause substantial effect on the cellular activities and bone tissue formation when applied exogenously. Second, the magnitude and duration of the changes in zeta potential are related to an ion exchange between the hydrated layer around the ceramic and the ceramic surface, and a net precipitation of new material. If these findings could be confirmed in other solutions, i.e., solutions with a substantially equivalent composition as the fluids in developing bone tissue, a basis would be provided to explain the bridging of the ceramic surface with the surrounding developing tissue.

Biocompatible Materials↗
PubMed2005

Seasonal variations in circadian rhythms coincide with a phase of sensitivity to short photoperiods in the European hamster.

European hamsters (Cricetus cricetus) show pronounced seasonal changes in their physiology and behavior. The present study provides a detailed analysis of the temporal relationship between seasonal cycles of reproduction and body mass and seasonal changes of two circadian parameters, i.e., locomotor activity and 6-sulphatoxymelatonin (aMT6s) excretion, in individual animals kept under natural light conditions. Our results demonstrate a characteristic pattern of locomotor activity and aMT6s excretion observed around the summer solstice, i.e., from mid-May to mid-July. During this time, locomotor activity was characterized by a high level of activity and an early activity onset, while the nightly elevation of melatonin was reduced to baseline levels. These seasonal changes in aMT6s excretion and locomotor activity were only loosely related to changes in the reproductive status of the animals, but correlated well with a period of the annual cycle during which the animals were sensitive to short days. They may therefore reflect a specific state of the circadian pacemaker system within the SCN and can thus be a valuable tool to further characterize molecular and physiological mechanisms of photoperiodic time measurements in European hamsters.

Animals↗
PubMed1998

Cell cycle regulation by plant growth regulators: involvement of auxin and cytokinin in the re-entry of Petunia protoplasts into the cell cycle.

In order to understand the mode of action of auxins and cytokinins in the induction of cell division, the effects of the two plant growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D) and N6-benzyladenine (BA) were investigated using mesophyll protoplasts of Petunia hybrida, cultivated in either complete medium or in medium deficient in cytokinin, auxin or both. Firstly we studied DNA synthesis, using 5-bromodeoxyuridine/bisbenzimide Hoechst/propidium iodide flow cytometry analyses and by the monitoring of histone H4 transcript levels. Roscovitine, a cyclin-dependent kinase (CDK) inhibitor, was found to block the cell cycle prior to entry into the S and M phases in the cultured P. hybrida protoplasts. This suggests that in Petunia cell there is a requirement for CDK activity in order to complete the G1 and G2 phases. Further experiments using roscovitine showed that neither 2,4-D nor BA were individually able to induce cell cycle progression beyond the roscovitine G1 arrest. We also monitored the phytohormonal induction of S phase by studying variations in transcript levels of the gene for mitogenactivated protein kinase (PMEK1) and transcript levels of the cell division cycle gene cdc2Pet. Only 2,4-D, and not BA, was able to stimulate PMEK1 gene transcription; thus, the more rapid S-phase induction in 2,4-D-treated protoplasts may be attributable to the activation of this transduction pathway. In contrast, both plant growth regulators were required to induce the appearance of cdc2Pet mRNA transcripts prior to S-phase engagement.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1986

Conformational effects in the high-performance liquid chromatography of proteins. Further studies of the reversed-phase chromatographic behavior of ribonuclease A.

This paper is a continuation of an examination of the conformational effects of ribonuclease A (RNase A) in reversed-phase liquid chromatography. RNase A is a particularly good example of reversible conformational refolding during chromatographic elution. Absorbance ratio measurements with a photodiode-array detector are consistent with a two-state model in which an early eluted broad band is associated with the folded or native state and a late eluted sharp band is associated with an unfolded state. By varying the mobile phase flow-rate while maintaining the mean capacity factor (k') of the protein in gradient elution constant, the apparent rate constant of refolding in the mobile phase was measured and found to be comparable with that reported in the literature. It has been further shown that, as the gradient steepness parameter b or mean k' value is altered, the apparent rate constant also changes, as a result of variation in mobile phase composition. The apparent rate constant as a function of temperature was also found to reach a maximum at 20 degrees C. Based on the results of this model system, it is possible to predict optimum conditions for elution of species with sharp elution peaks when reversible refolding takes place in the column.

Chemical Phenomena↗
PubMed1982

Comparison of soleus H reflex facilitation at the onset of soleus contractions produced voluntarily and during the stance phase of human gait.

Variations in the soleus monosynaptic reflex have been studied in normal human subjects during soleus contractions while walking, and compared with those observed during voluntary soleus activation. The monosynaptic reflex was always more facilitated during voluntary contractions than during walking. The EMG activity was identical in both situations. Under the assumption that this reflects an identical excitability of the motoneuronal pool, this different soleus H-reflex facilitation can be attributed to a difference in the excitatory efficiency of the group I volley evoked by the H-reflex stimulation. It is suggested that the level of presynaptic inhibition exerted on Ia fibers could be lower during walking than during voluntary contraction.

Ankle↗
PubMed1989

Variation in the length of the lag phase following serum restimulation of mouse 3T3 cells.

We have investigated the length of the lag phase (time taken for the first cells to enter S phase) and the kinetics of entry into DNA synthesis after serum restimulation of Swiss mouse 3T3 cell cultures that were allowed to become quiescent under different conditions. Cells were allowed to reach quiescence as a confluent monolayer in medium containing 10% (v/v) calf serum. Alternatively, when serum was reduced to 1% (v/v), cultures became quiescent at about 30% confluency and there was little cell to cell contact. The results show that the lag, or prereplicative phase becomes longer as the time spent in the quiescent state increases. This is the case in both confluent and non-confluent cultures. The rate of entry of cells into the S phase, however, remains the same under all conditions.

Animals↗
PubMed2005

Looking inside the pores of a chromatographic column. I. Variation of the pore volume with mobile phase composition.

The dependence of void volume and pore volume on mobile phase composition was studied on a reversed phase column based on poly(divinyl benzene) in mobile phases consisting of 100% tetrahydrofuran (THF) and 40-90% THF-water. Void volumes V0 are obtained from a series of polymers with different molar mass by extrapolation of elution volume to M = 0, the interstitial volume Vi from the elution volume of polymers with a sufficiently high molar mass. The pore volume Vp is obtained as the difference (V0 - Vi). While Vi does not depend on mobile phase composition, a dramatic decrease of the pore volume is observed, when the mobile phase is changed from THF to THF-water. This effect of the mobile phase composition on the pore volume is observed using PEG and PPG as test macromolecules, regardless the retention mechanism: at 40-50% THF both PEG (in exclusion mode) and PPG (in adsorption mode) experience the same reduced pore volume, which is considerably lower than that in 100% THF.

Adsorption↗
PubMed1998

Variation of penicillin acylase partition coefficient with phase volume ratio in poly(ethylene glycol)-sodium citrate aqueous two-phase systems.

The influence of phase volume ratio on partition and purification of penicillin acylase from Escherichia coli on poly(ethylene glycol)-sodium citrate aqueous two-phase systems was studied. In PEG 1000 systems both partition coefficients of the enzyme and total protein increased with decreasing phase volume ratio. However, in PEG 3350 containing NaCl, penicillin acylase follows a reverse trend, while total protein behaves in the same way. Implications for protein purification designs are discussed.

Chemistry Techniques, Analytical↗