Les neurones sensoriels myentériques (étude in situ par la technique de Patch Clamp)

Les principaux courants ioniques des neurones myentériques AH in situ ont été étudiés en patch clamp dans le duodenum de cobaye. Ih régule la résistance d'entrée des neurones AH. La conotoxine GVIA, mais pas l'agatoxine IVA, abrège le potentiel d'action et bloque l'AHP qui est donc couplée aux canaux Ca2+ de type N. Nous avons aussi découvert un courant Na+ résistant à la TTX (TTX-R INa). TTX-R INa s'active et s'inactive lentement et possède une composante persistante. La substitution du Cl-intracellulaire par le F- hyperpolarise les paramètres dépendants du voltage de TTX-R INa, lui conférant les propriétés de NaN/NaV1.9 dans les DRG. Des expériences de RT-PCR, single cell RT-PCR et immunohistochimie indiquent que l'ARNm et la sous-unité NaV1.9 sont présents dans les neurones AH. Dans les neurones AH, NaN présente aussi une inactivation originale associant une diminution ultra lente ( max=100 s) de NaN à un ralentissement des cinétiques d'activation (m) et d'inactivation (hf).AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF

Kinetic properties of mechanically activated currents in spinal sensory neurons

Dorsal root ganglion neurons in vitro express a number of types of mechanically activated currents that are thought to underlie somatic mechanosensory transduction in vivo. We have studied the inactivation properties of these currents to assess how they might influence the electrophysiological responses of dorsal root ganglion (DRG) neurons to mechanical stimulation. We show that the speed of ramp-like mechanical stimulation determines the dynamics of mechanically activated current responses and hence the type of DRG neuron most likely to be activated. We also show that both rapidly and slowly adapting currents inactivate as a function of membrane stretch. However, the rapidly adapting current inactivation time course is mainly dependent on channel opening whilst slowly adapting current kinetics are dependent on membrane stretch. In response to repeated stimulation, slowly adapting currents inactivate less and recover more quickly than rapidly adapting currents. Therefore, vibratory stimuli tend to inactivate rapidly adapting currents whilst static stimuli tend to inactivate slowly adapting currents. Current clamp experiments show that, physiologically, the response of different types of sensory neurons is dictated primarily by the static or dynamic nature of the mechanical stimulus and the interplay between voltage-gated and mechanically gated ion channels expressed in these neurons

Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity

Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging