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Biomedical subjects

D Bertrand

Publications and source records attributed to D Bertrand.

At least 181 records · Page 10Linked to original sources
PubMed1985

Study of a neuronal potassium current in different culture conditions.

The potassium current of neurons in explants cultured from quail mesencephalic neural crest were studied in voltage clamp, using the whole cell recording technique. Two voltage-dependent potassium currents were identified; they differed in their sensitivity to blocking agents and to sustained depolarizing voltages. The potassium current component most sensitive to 4-aminopyridine had fast activation kinetics and inactivated quickly at sustained depolarized voltages. By analogy with a current described in other preparations, this current was called IA. The current component most sensitive to tetraethylammonium had slower activation kinetics and inactivated more slowly than IA at sustained depolarized voltages. This current was called IK. The properties of IA and IK were examined in neurons cultured in a defined medium and in neurons co-cultured with striated muscle. The rate of inactivation of IA appeared to be increased when neural crest neurons were cultured in the presence of striated muscle. The change in the properties of IA could be due to a direct effect of the co-culture with muscle on the membrane current; another possibility could be that co-culture favors the survival of a neuronal population that does not survive well when cultured in a defined medium.

4-Aminopyridine↗
PubMed1985

Haemodynamic effects of inspiratory and expiratory resistances in anaesthetic breathing systems during induced hypotension.

This study was aimed at determining the haemodynamic effects of various flow resistances in the anaesthetic breathing system in 15 patients under induced hypotension. The breathing pattern, arterial blood gases and haemodynamics were analysed during spontaneous breathing with three systems with different flow resistance as compared with a low-resistance control system. One was made up of a Digby-Leigh valve with an inspiratory resistance of 7 cmH2O l-1s and a high expiratory resistance of 25 cmH2O l-1s (DLS); the other two had an added inspiratory resistive load of 12 cmH2O l-1s (IRS1) and 25 cmH2O l-1s (IRS2) respectively. Whichever system was used, blood gases did not change. With DLS, pulmonary arterial and wedge pressures increased. With the two high inspiratory resistance systems, stroke volume (SV) increased and heart rate (HR) decreased. In six patients, SV was increased only with IRS2, whereas the increase seen with IRS1 in the other nine subjects disappeared with IRS2. It is concluded that the expiratory resistance should be as low as possible in order to avoid pulmonary haemodynamic consequences. An inspiratory resistive load, carefully adapted to each individual case, produced an increase in SV probably by enhancing the venous return. This latter effect could be beneficial in reducing bleeding during middle ear micro-surgery.

Acid-Base Equilibrium↗
PubMed1984

Effect of changes in intra- and extracellular sodium on the inward (anomalous) rectification in salamander photoreceptors.

Solitary rod inner segments were obtained by enzymic dissociation of the tiger salamander retina. Ih, an inward current activated by membrane hyperpolarization, was studied using the single-pipette voltage-clamp technique with patch pipettes. In order to investigate Ih in isolation from voltage-dependent potassium and calcium currents, it was necessary to superfuse with a solution containing TEA and cobalt. When the solution in the patch pipette contained 45 mM-KCl and 50 mM-NaCl, the characteristics of Ih were indistinguishable from those previously described with fine-tip micro-electrodes: the reversal potential was near-30 mV and Ih was blocked by extracellular caesium and enhanced by an increase in the extracellular potassium concentration. The increase in Ih observed when the extracellular potassium concentration is raised is due to an increase in conductance and in driving force. Replacement of sodium in the patch pipette with choline caused a 15 mV displacement of the reversal potential for Ih in the depolarized direction. When using sodium-free patch pipettes, replacement of extracellular sodium displaced the reversal potential for Ih to -74 mV, a value in the range of the potassium equilibrium potential in solitary inner segments. Intracellular or intra- and extracellular sodium substitution affected neither the activation range of Ih nor the maximum conductance. From points 3-6 it can be concluded that Ih is carried mainly, if not exclusively, by sodium and potassium and that the channel responsible for Ih is insensitive to modifications of the intra- or extracellular sodium concentration. The results of long-term hyperpolarization, of partial block with caesium and of total sodium substitution are consistent with sodium and potassium permeating the same type of channel.

Action Potentials↗
PubMed1983

Membrane currents in a developing parasympathetic ganglion.

It is reported that chick embryo ciliary ganglion neurons that have just terminated their migration and are in the process of forming a ganglion express several properties underlying membrane excitability. Evidence is presented which suggests that these cells possess voltage-dependent sodium, potassium, and calcium currents as well as a calcium-activated potassium current. These currents resemble those previously described in the more mature ciliary ganglion (Bader, C. R., Bertrand, D., and Kato, A. C. (1982). Dev. Biol. 94, 131-141) but may differ in their density per unit membrane surface. For example, the density per unit surface of the voltage dependent sodium current in younger neurons appears to be 5 to 10 times smaller than in more mature neurons.

Action Potentials↗
PubMed1983

Effects of induced hypotension on breathing pattern in halothane-anaesthetized man.

The effects of hypotension induced by trimetaphan on ventilatory control were assessed in sixteen normal subjects under halothane anaesthesia. The breathing pattern, mouth occlusion pressures, lung mechanics, acid-base balance, and arterial blood gases were analysed before and during trimetaphan infusion. During induced hypotension, the only significant change in the ventilatory variables was an increase in the ratio of inspiratory duration to total cycle duration from 0.39 +/- 0.05 (SD) to 0.42 +/- 0.03; P less than 0.01. The average minute ventilation remained unchanged. No modification in lung mechanics was observed, but all subjects developed a slight but significant hypocapnic alkalosis: PaCO2 was reduced from 5.5 +/- 0.4 to 5.2 +/- 0.4 kPa (P less than 0.001) and pH increased from 7.34 to 7.36 (P less than 0.05), without change in standard bicarbonate concentration. Our data indicate that the reduction in sympathetic nervous system activity induced by trimetaphan infusion in spontaneously breathing man causes only a minor alveolar hyperventilation. The weak respiratory response to hypotension suggests that changing peripheral afferent activity has little influence on the typically rapid breathing pattern induced by halothane.

Acid-Base Equilibrium↗
PubMed1982

Diffuse and local effects of light adaptation in photoreceptors of the honey bee drone.

Intracellular recordings from drone photoreceptors were made by means of glass microelectrodes in superfused retinae. Exposure of a small portion of a cell to white light decreased the amplitude of responses to a small stimulus subsequently applied at different sites of the photoreceptor cell, i.e. light adaptation occurred throughout the cell. After 7 min of darkness, the responses had completely recovered. When a violet light (404 nm) was used to adapt a small portion of the cell, the responses at the site of exposure to the adapting stimulus remained depressed for at least 30 min. Illumination at the site of the violet adapting stimulus with green light (585 nm) caused an immediate recovery of the amplitude of the response. These results can be explained by the existence of two processes responsible for light adaptation: one is localized and persistent and appears to be due to changes in concentration of rhodopsin. The other affects the whole cell, is spontaneously reversible and depends upon the ability of the light to produce a receptor potential but not on any lasting change in rhodopsin concentration.

Action Potentials↗
PubMed1982

Voltage-activated and calcium-activated currents studied in solitary rod inner segments from the salamander retina.

1. Solitary rod inner segments were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. Their membrane currents were studied with the single-pipette voltage-clamp technique. Individual currents were isolated with the aid of pharmacological agents.2. Extracellular caesium blocked a current activated by hyperpolarization from -30 mV. Changing external sodium and potassium concentrations altered the value of the reversal potential in a manner consistent with the current being carried equally by both ions.3. Extracellular tetraethylammonium (TEA) blocked a current activated by depolarization from -70 mV. In normal medium this current had a reversal potential of -72 mV. Changing the external potassium concentration altered the value of the reversal potential in a manner consistent with the current being carried predominantly by potassium.4. Extracellular cobalt blocked a current activated by depolarization that had an initial inward and a later outward component.5. After EGTA was injected into an inner segment the outward component was suppressed. Cobalt then blocked an inward current. This current is believed to be carried predominantly by calcium. The conductance increased with depolarization from -45 mV and reached a maximum at approximately 0 mV. Following a step of depolarization the current activated rapidly (< 20 msec) and then remained constant for at least several seconds without evidence of inactivation.6. Injecting caesium into an inner segment eliminated a calcium-activated outward current believed to be carried by potassium ions.7. After the injection of caesium there remained another calcium-activated current with a reversal potential of -17 mV. Changing extracellular chloride concentration altered the value of the reversal potential in a manner consistent with chloride carrying at least 70% of the current. Another anion may carry the balance.8. When the five currents mentioned in items 2, 3, 5, 6 and 7 were blocked, the membrane resistance between -90 and -25 mV was linear, time-independent, and had a high value (2.1 GOmega).9. The five identified currents can all be activated in the physiological range of voltage in which salamander rods normally operate.

Action Potentials↗
PubMed1981

[The respiratory effects of small dose fentanyl associated with controlled hypotension during spontaneous ventilation in anesthetized man (author's transl)].

Deliberately lowering blood pressure facilitates middle ear surgery. However, bleeding can persist in spite of hypotension in some tachypneic patients. Fentanyl is a powerful morphinomimetic which decreases ventilatory frequency. This work studies the respiratory effects of fentanyl during spontaneous ventilation in 16 anesthetized patients. Their systemic blood pressure was decreased 40 per cent by trimetaphan. One single injection of fentanyl (0.0125 mg) reduced minute ventilation by 26 per cent, mean inspiratory flow rate (VT/T1) and T1/TTOT, but did not modify the pulmonary dynamic compliance. The acid-base balance parameters changed little toward respiratory alkalosis by trimetaphan and returned to their control values after the injection of fentanyl. Thus, a small dose of fentanyl can be combined with controlled hypotension during anesthesia and spontaneous ventilation without respiratory risk or an acid-base inbalance. With this dose, it has an efficient central influence to reduce the breathing frequency and can be used to lessen bleeding.

Acid-Base Equilibrium↗
PubMed1980

Storage and retrieval of bibliographic references using a microprocessor system.

A program is described for the storage and retrieval of bibliographic references. The program, designed for a dual floppy disk microcomputer system, allows fast access to references, which can be retrieved by keywords, by authors' names or by string matching. Provided a printer is available, the program prints reprint requests, while new references are being stored, and prints hard copies of the references. The program also includes the possibility of creating a new bibliographic file from one or more already existing files.

Bibliographies as Topic↗