An allosteric gating model recapitulates the biophysical properties of IK,L expressed in mouse vestibular Type I hair cells

Type I and Type II hair cells are the sensory receptors of the mammalian vestibular epithelia. Type I hair cells are characterized by their basolateral membrane being enveloped in a single large afferent nerve terminal, named calyx, and by the expression of a low-voltage-activated outward rectifying K(+) current, IK,L . The biophysical properties and molecular profile of IK,L are still largely unknown. By using the patch-clamp whole-cell technique, we examined the voltage- and time-dependent properties of IK,L in Type I hair cells of the mouse semicircular canal. We found that the biophysical properties of IK,L were affected by an unstable K(+) equilibrium potential (Veq K(+) ). Both the outward and inward K(+) currents shifted Veq K(+) consistent with K(+) accumulation or depletion, respectively, in the extracellular space, which we attributed to a residual calyx attached to the basolateral membrane of the hair cells. We therefore optimized the hair cell dissociation protocol in order to isolate mature Type I hair cells without their calyx. In these cells, the uncontaminated IK,L showed a half-activation at -79.6 mV and a steep voltage dependence (2.8 mV). IK,L also showed complex activation and deactivation kinetics, which we faithfully reproduced by an allosteric channel gating scheme where the channel is able to open from all (five) closed states. The "early" open states substantially contribute to IK,L activation at negative voltages. This study provides the first complete description of the "native" biophysical properties of IK,L in adult mouse vestibular Type I hair cells. This article is protected by copyright. All rights reserved

Pig production : short-term prospects

International audienc

Conséquences de la non prise en compte de la détectabilité des espèces dans les analyses ACP et AFC.

Les analyses factorielles sont couramment utilisées en écologie pour analyser les données multivariées. Ces analyses fournissent des ordinations permettant de visualiser les principaux facteurs de variations au sein des données dans des graphiques en deux dimensions. Les tableaux regroupant les données d’abondances ou de présences de plusieurs espèces sur plusieurs sites peuvent être explorés à l’aide de ces analyses. Dans ces derniers cas cependant, la question des conséquences sur les résultats de ces analyses, de la non prise en compte du fait que la probabilité de détection des espèces sur le terrain est généralement inférieure à un lors de l’élaboration des tableaux de données, n’a jamais été clairement posée.Pour aborder cette question, je me suis concentré sur deux analyses factorielles classiques que sont les Analyses en Composantes Principales (ACP) et les Analyses Factorielles des Correspondances (AFC). Pour chacune des analyses, j’ai comparé les résultats obtenus à partir d’un tableau d’abondances simulé avec une probabilité de détection égale à un, avec ceux obtenus à partir du même tableau simulé cette fois avec des probabilités de détection inférieures à un. Je me suis limité aux cas où la probabilité de détection s’organisait selon un gradient, plus ou moins complexe, entre sites et entre espèces. Mes simulations montrent que les résultats des analyses sont dégradés par la non prise en compte de la probabilité de détection. Ces dégradations sont multifactorielles et sont donc variées. Les ordinations proposées par les analyses peuvent être le reflet, partiel ou total, de l’hétérogénéité de la probabilité de détection entre les espèces ou/et les sites. Aussi, certains facteurs de variations entre sites et espèces existant réellement peuvent ne plus apparaître dans les résultats des analyses sur les tableaux impactés par des probabilités de détection inférieures à un. L’application de telles analyses sur des tableaux d’abondances qui ne prennent pas en compte la probabilité de détection, peut donc mener à des conclusions erronées. Ceci me conduit à recommander fortement de prendre en compte la probabilité de détection en amont de ces analyses sur des tableaux d’abondances, par exemple à travers l’utilisation de méthodes telles que le Distance sampling ou le N–mixture. Ces travaux appellent aussi au développement de méthodes spécifiques combinant l’estimation de ces probabilités de détection et l’ordination des sites et des espèces

Main characteristics of French pig production. Main results of the pig survey made in December 1981

International audienc

Neurotransmission de la synapse en calice vestibulaire

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Natural grasslands in the Massif Central: expressing regional identity through high-quality products

The often natural grasslands of the Massif Central (80% of usable farm area) contain an impressive pool of native species. They are also a resource that can enhance the quality of the region's livestock products. Over a decade of constructive research and development partnerships have led to the development of two multifunctional tools that can characterise grassland resources and the products they generate. A classification system has been created that describes the agricultural and environmental potential of 70 types of grasslands, as well as the relative quality of the resulting products. With the DIAM diagnostic tool, it is possible to design customised plans for individual farmers based on their farming strategies and the types of grasslands present on their farms. Both tools underscore the important role natural grasslands can play in generating high-quality products

Glutamate transporters EAAT4 and EAAT5 are expressed in vestibular hair cells and calyx endings.

Glutamate is the neurotransmitter released from hair cells. Its clearance from the synaptic cleft can shape neurotransmission and prevent excitotoxicity. This may be particularly important in the inner ear and in other sensory organs where there is a continually high rate of neurotransmitter release. In the case of most cochlear and type II vestibular hair cells, clearance involves the diffusion of glutamate to supporting cells, where it is taken up by EAAT1 (GLAST), a glutamate transporter. A similar mechanism cannot work in vestibular type I hair cells as the presence of calyx endings separates supporting cells from hair-cell synapses. Because of this arrangement, it has been conjectured that a glutamate transporter must be present in the type I hair cell, the calyx ending, or both. Using whole-cell patch-clamp recordings, we demonstrate that a glutamate-activated anion current, attributable to a high-affinity glutamate transporter and blocked by DL-TBOA, is expressed in type I, but not in type II hair cells. Molecular investigations reveal that EAAT4 and EAAT5, two glutamate transporters that could underlie the anion current, are expressed in both type I and type II hair cells and in calyx endings. EAAT4 has been thought to be expressed almost exclusively in the cerebellum and EAAT5 in the retina. Our results show that these two transporters have a wider distribution in mice. This is the first demonstration of the presence of transporters in hair cells and provides one of the few examples of EAATs in presynaptic elements

Glutamate Transporters EAAT4 and EAAT5 Are Expressed in Vestibular Hair Cells and Calyx Endings

Glutamate is the neurotransmitter released from hair cells. Its clearance from the synaptic cleft can shape neurotransmission and prevent excitotoxicity. This may be particularly important in the inner ear and in other sensory organs where there is a continually high rate of neurotransmitter release. In the case of most cochlear and type II vestibular hair cells, clearance involves the diffusion of glutamate to supporting cells, where it is taken up by EAAT1 (GLAST), a glutamate transporter. A similar mechanism cannot work in vestibular type I hair cells as the presence of calyx endings separates supporting cells from hair-cell synapses. Because of this arrangement, it has been conjectured that a glutamate transporter must be present in the type I hair cell, the calyx ending, or both. Using whole-cell patch-clamp recordings, we demonstrate that a glutamate-activated anion current, attributable to a high-affinity glutamate transporter and blocked by DL-TBOA, is expressed in type I, but not in type II hair cells. Molecular investigations reveal that EAAT4 and EAAT5, two glutamate transporters that could underlie the anion current, are expressed in both type I and type II hair cells and in calyx endings. EAAT4 has been thought to be expressed almost exclusively in the cerebellum and EAAT5 in the retina. Our results show that these two transporters have a wider distribution in mice. This is the first demonstration of the presence of transporters in hair cells and provides one of the few examples of EAATs in presynaptic elements.</p