PubMed Health⌕ Search

Biomedical subjects

D Trotier

Publications and source records attributed to D Trotier.

12 recordsLinked to original sources
PubMed1996

Direct influence of the sodium pump on the membrane potential of vomeronasal chemoreceptor neurones in frog.

1. Whole-cell measurements were made from microvillous receptor neurones isolated from the frog vomeronasal organ. We examined the mechanisms that determined the value of the resting membrane potential. 2. Cells recorded in Ringer solution containing 4 mM K+ showed a resting membrane potential of -88 +/- 20 mV (mean +/- 1 S.D., n = 56). Sixty-six per cent of the cells had stable resting potentials more negative than the calculated equilibrium potentials for K+ (EK, -82 mV) indicating the presence of a hyperpolarizing outward pump current. 3. Cells recorded with an intracellular solution containing Na+ instead of K+, to set EK at 0 mV, presented stable membrane potentials in the range -65 to -119 mV when bathed in a normal Ringer solution. 4. Ouabain, a specific inhibitor of the Na+,K(+)-ATPase, blocked the outward sodium pump current (Ip) and depolarized the membrane. 5. The sodium pump current, measured as the current blocked by 0.5 mM dihydro-ouabain, was linearly related to the membrane potential in the range -60 to -120 mV. The reversal potential measured with a calculated free energy of ATP hydrolysis of -36.2 kJ mol-1 was estimated to be -143 mV. 6. Reduction of the external K+ concentration to 0 mM depolarized the membrane to less than -40 mV. Voltage-clamp observations in this condition indicated a reduction of Ip. Ouabain added to the bath reduced the blocking effect of low external K+. The addition of external K+ activated Ip and induced a rapid hyperpolarization of the cell membrane. 7. At membrane potentials more negative than -80 mV, an inward rectifying depolarizing current characterized as Ih was activated. When Ih was blocked by 5 mM external Cs+ the resting membrane potential increased. 8. These data indicate that the membrane potential of the vomeronasal receptor neurones is not generated by a passive diffusion of K+ ions but by the hyperpolarizing current created by the Na+,K(+)-ATPase. We propose that the resting potential is set by a balance between Ip and Ih. The physiological implications of these mechanisms for setting the resting potential are discussed.

Animals↗
PubMed1996

[The vomeronasal organ--a rediscovered sensory organ].

The authors review the function and anatomy of the vomeronasal organ (organ of Jacobson), a chemosensory organ situated in the nose. In mammals, stimulation of the vomeronasal organ induces sexual behaviour and changes the hormonal status of males and females. Impairment of the vomeronasal organ in rats disrupts both the females' ultrasound calling during oestrus and their maternal behaviour. Stimulation of the vomeronasal organ promotes sexual maturation of juvenile females and induces abortion and production of pheromones. Earlier on, the vomeronasal organ in man was believed to be present only at the foetal stage; in 1991 its presence was reestablished in adults. Electrophysiological studies show that the vomeronasal organ of man is stimulated by steroids found in human skin. The physiological properties of the receptor cells of the vomeronasal organ are different from those of the olfactory organ.

Adolescent↗
PubMed1996

Functional role of receptor neurons in encoding olfactory information.

In the present review we have considered the properties of the olfactory receptor neurons and discuss the strategy these cells use to perform their signaling task. Special emphasis is laid on the mechanisms for setting the membrane potential at rest and the mechanisms that the cell can use to respond with action potentials to significant stimuli only. We demonstrate that the firing properties of the receptor neurons depend upon the initial level of the membrane potential. We present the idea that the olfactory glomerulus can function as a unit in olfactory processing. In this perspective the olfactory receptor neuron is a subunit of the olfactory glomerulus.

Action Potentials↗
PubMed1994

Intensity coding in olfactory receptor cells.

Olfactory receptors code the concentration of stimulating molecules into an impulse frequency message. Patch-clamp recordings have now demonstrated, in the olfactory receptor cell membrane, a number of membrane conductances. Some of them are gated by odorants, in the cilia, and depolarize the cell through cAMP- or IP3-sensitive channels, depending on the species. Other conductances are activated by membrane depolarization and/or an increased intracellular Ca2+ concentration; they participate in oscillating membrane potential changes during impulses and post-spike after-polarizations, and control the repetitive firing. Original data relative to the resting potential and the impulse frequency coding of the odorant concentration are presented.

Action Potentials↗
PubMed1994

A new clinical olfactory test to quantify olfactory deficiencies.

We have recently developed a computer-assisted olfactory test to measure detection thresholds for five pure odorants. The reference group consisted of 30 subjects without olfactory complaints. Statistical analysis was carried out to identify a statistical criterion for determining olfactory deficiencies. This criterion was applied to 54 subjects suspected to have an olfactory deficiency, either on the basis of their subjective complaints or on clinical examinations (e.g. scanner radiography, endoscopic investigations, rhinomanometric measurements). Nine aetiological groups were screened: trauma, nasal polyposis, nasal obstruction, allergic rhinitis, post-influenza, post-anaesthesia, endocrine dysfunction, hereditary hyposmia, and subjective olfactory loss without a clear aetiology. In each group, this method allowed us to discriminate between deficient and non-deficient patients, and the olfactory deficit could be quantified. This rapid procedure was well-accepted by all subjects and gave reproducible quantitative results. It can provide useful information about the relationship between olfactory acuity and a given aetiologic category.

Humans↗
PubMed1993

Voltage-dependent currents in microvillar receptor cells of the frog vomeronasal organ.

Vomeronasal receptor cells are differentiated bipolar neurons with a long dendrite bearing numerous microvilli. Isolated cells (with a mean dendritic length of 65 microns) and cells in mucosal slices were studied using whole-cell and Nystatin-perforated patch-clamp recordings. At rest, the membrane potential was -61 +/- 13 mV (mean +/- SD; n = 61). Sixty-four per cent of the cells had a resting potential in the range of -60 to -86 mV, with almost no spontaneous action potential. The input resistance was in the G omega range and overshooting repetitive action potentials were elicited by injecting depolarizing current pulses in the range of 2-10 pA. Voltage-dependent currents were characterized under voltage-clamp conditions. A transient fast inward current activating near -45 mV was blocked by tetrodotoxin. In isolated cells, it was half-deactivated at a membrane potential near -75 mV. An outward K+ current was blocked by internal Cs+ ions or by external tetraethylammonium or Ba2+ ions. A calcium-activated voltage-dependent potassium current was blocked by external Cd2+ ions. A voltage-dependent Ca2+ current was observed in an iso-osmotic BaCl2 solution. Finally, a hyperpolarization-activated inward current was recorded. Voltage-dependent currents in these microvillar olfactory receptor neurons appear qualitatively similar to those already described in ciliated olfactory receptor cells located in the principal olfactory epithelium.

Animals↗
PubMed1991

Odorant-evoked potassium changes in the frog olfactory epithelium.

Electroolfactogram (EOG) and extracellular potassium activity (aK) measurements were carried out in frog olfactory epithelia in vivo. Odorant-evoked changes in aK were characterized on the basis of depth profile analysis. Following an olfactory stimulation with butanol vapours, an increase in aK was measured in the mucus and the proximal part of the epithelium; this response started after the beginning of the EOG and was proportional to the amplitude of the latter. In the deeper part of the epithelium, the aK response had complex waveforms showing an initial K decrease which was suppressed by local application of ouabain, suggesting the existence of a pumping mechanism at this level. The results are discussed in terms of extracellular accumulation of K ions following neuroreceptor activation with respect to EOG generation theories.

Animals↗
PubMed1991

Luminal non-specific cationic channels in cultured strial marginal cells of guinea pig and gerbil as determined by patch clamp technique.

Using primary cultures of marginal cells of stria vascularis from guinea pig and gerbil, ionic channels located on the luminal membrane were investigated by means of patch clamp technique. Recordings were performed in cell-attached and inside-out configurations. In cell-attached configuration, single channel activity was identified with a conductance of about 25 pS. I-V curve was linear. The probability of opening was increased upon depolarization. Up to 7 channels could be present in the same patch, indicating a rather high density. In inside-out configuration, the reversal potential was 0 mV, suggesting a non-specific cationic channel. These luminal non-specific cationic channels would allow the passive K+ efflux and Na+ influx across the apical membrane of marginal cells. This finding is consistent with the "one-pump" model of strial activity. The present study suggests that culture of strial marginal cells may be a suitable model for in-depth investigation of endolymph physiology.

Animals↗
PubMed1986

Intracellular recordings from salamander olfactory supporting cells.

Stable intracellular potentials were recorded just below the surface of the salamander olfactory epithelium. The site of recording corresponded to the zone of highest density of supporting cell perikarya. The electrophysiological properties of cells recorded in this zone included: neither spontaneous nor evoked spike activity, high resting potential (-96 +/- 10 mV, n = 113) and low input resistance (15 +/- 12 M omega, n = 64). The cells were depolarized to -9 +/- 8 mV when the extracellular potassium concentration was increased from 2 to 100 mM. The membrane potential also changed during activation of the olfactory receptor neurons. Antidromic stimulation of olfactory axons elicited both rapid and slow depolarizations. Odorant stimulation induced graded depolarizations which always lagged behind the electro-olfactogram by more than 1 s. In contrast to the responses of the olfactory receptor neurons, these responses were nearly identical from one cell to another. Compared with the concomitant electro-olfactogram, they had almost the same amplitude, with a reversed polarity. These findings are discussed in the context of the possible auxiliary functions of supporting cells in olfactory processes.

Animals↗
PubMed1986

A patch-clamp analysis of membrane currents in salamander olfactory receptor cells.

Isolated olfactory receptor cells were obtained from salamander olfactory epithelium and kept in short term culture conditions. They were studied by means of the whole cell patch-clamp technique associated with ionic substitutions and channel blockers. Under physiological ionic gradients, these cells had a resting potential of -39 +/- 10 mV and an input resistance above 2 G omega. Using different channel blockers and ion substitutions, we could separate several distinct components in the overall whole cell current. In most cells, inward current reflected the activation of a TTX resistant conductance which was blocked by cobalt ions. This inward current lasted only for about 5 min of whole cell recording. In a minority of cells, a TTX sensitive sodium current was also observed. The outward K+ current was blocked when the cells were loaded with cesium and tetraethylammonium. It inactivated slowly and incompletely and could act as a depolarization limited in case of intense odour stimulations. Single channel analysis from outside out patches suggested that it corresponded to the activity of 34 pS channels. In some cells a rapidly inactivating K+ current was also present. Single channel activities (27 +/- 6 pS) were commonly recorded with KCl-filled pipettes, at resting or hyperpolarized membrane potentials but not at depolarized potentials. Membrane hyperpolarization increased the open-state probability. A preliminary study with odorant stimulations indicated the existence of a stimulus-induced current probably corresponding to the activation of the chemoreceptive membrane.

Animals↗
PubMed1983

Intracellular recordings from salamander olfactory receptor cells.

Intracellular recordings were obtained from salamander olfactory receptor cells. The occurrence of an intracellular spike in response to the antidromic stimulation of the olfactory fibers was considered as a physiological criterion of a neuronal impalement. The mean resting potential was -56 +/- 9 mV (mean +/- S.D.; n = 70). Fifty-two cells presented a spontaneous spike activity lower than 2 impulses/s. Appropriate olfactory stimulation generally evoked a slow and graded decrease (up to 28 mV) of the intracellular potential. The input resistance of the cell decreased markedly during the response. The slow potential change induced a repetitive firing. Increasing the intensity of the olfactory stimulation increased the instantaneous frequency of firing (up to 25 s-1) and reduced the spike amplitude. The spikes presented an inflexion in the rising phase indicating a two-stage depolarization. With the strongest intensities of stimulation the impulse activity was stopped during the repolarizing phase of the cell response when the membrane potential was still appreciably depolarized.

Animals↗