The glutamate receptor GluK2 contributes to the regulation of glucose homeostasis and its deterioration during aging

OBJECTIVE: Islets secrete neurotransmitters including glutamate which participate in fine regulation of islet function. The excitatory ionotropic glutamate receptor GluK2 of the kainate receptor family is widely expressed in brain and also found in islets, mainly in alpha and gamma cells. alpha cells co-release glucagon and glutamate and the latter increases glucagon release via ionotropic glutamate receptors. However, neither the precise nature of the ionotropic glutamate receptor involved nor its role in glucose homeostasis is known. As isoform specific pharmacology is not available, we investigated this question in constitutive GluK2 knock-out mice (GluK2-/-) using adult and middle-aged animals to also gain insight in a potential role during aging. METHODS: We compared wild-type GluK2+/+ and knock-out GluK2-/- mice using adult (14-20 weeks) and middle-aged animals (40-52 weeks). Glucose (oral OGTT and intraperitoneal IPGTT) and insulin tolerance as well as pyruvate challenge tests were performed according to standard procedures. Parasympathetic activity, which stimulates hormones secretion, was measured by electrophysiology invivo. Isolated islets were used invitro to determine islet beta-cell electrical activity on multi-electrode arrays and dynamic secretion of insulin as well as glucagon was determined by ELISA. RESULTS: Adult GluK2-/- mice exhibit an improved glucose tolerance (OGTT and IPGTT), and this was also apparent in middle-aged mice, whereas the outcome of pyruvate challenge was slightly improved only in middle-aged GluK2-/- mice. Similarly, insulin sensitivity was markedly enhanced in middle-aged GluK2-/- animals. Basal and glucose-induced insulin secretion invivo was slightly lower in GluK2-/- mice, whereas fasting glucagonemia was strongly reduced. Invivo recordings of parasympathetic activity showed an increase in basal activity in GluK2-/- mice which represents most likely an adaptive mechanism to counteract hypoglucagonemia rather than altered neuronal mechanism. Invitro recording demonstrated an improvement of glucose-induced electrical activity of beta-cells in islets obtained from GluK2-/- mice at both ages. Finally, glucose-induced insulin secretion invitro was increased in GluK2-/- islets, whereas glucagon secretion at 2mmol/l of glucose was considerably reduced. CONCLUSIONS: These observations indicate a general role for kainate receptors in glucose homeostasis and specifically suggest a negative effect of GluK2 on glucose homeostasis and preservation of islet function during aging. Our observations raise the possibility that blockade of GluK2 may provide benefits in glucose homeostasis especially during aging.Transistors multimodaux sensibles aux ions à polymères ambivalents pour biocapteurs hybridesIdentification de biomarqueurs du stress et de l'inflammation des cellules B pancréatiques en explorant les communications inter-organes dans des modèles précliniques d'obésité et de diabète de type

Трехкоординатный пьезокерамический сканер на биморфных пьезо-элементах для зондового наномикроскопа

Предложена и исследована конструкция пьезокерамического сканера для наномикроскопов на основе диморфных пьезоэлементов. Построена и исследована модель сканера при помощи программы MicroCap 7.0

Vertical Organic Electrochemical Transistors and Electronics for Low Amplitude Micro‐Organ Signals

Electrical signals are fundamental to key biological events such as brain activity, heartbeat, or vital hormone secretion. Their capture and analysis provide insight into cell or organ physiology and a number of bioelectronic medical devices aim to improve signal acquisition. Organic electrochemical transistors (OECT) have proven their capacity to capture neuronal and cardiac signals with high fidelity and amplification. Vertical PEDOT:PSS-based OECTs (vOECTs) further enhance signal amplification and device density but have not been characterized in biological applications. An electronic board with individually tuneable transistor biases overcomes fabrication induced heterogeneity in device metrics and allows quantitative biological experiments. Careful exploration of vOECT electric parameters defines voltage biases compatible with reliable transistor function in biological experiments and provides useful maximal transconductance values without influencing cellular signal generation or propagation. This permits successful application in monitoring micro-organs of prime importance in diabetes, the endocrine pancreatic islets, which are known for their far smaller signal amplitudes as compared to neurons or heart cells. Moreover, vOECTs capture their single-cell action potentials and multicellular slow potentials reflecting micro-organ organizations as well as their modulation by the physiological stimulator glucose. This opens the possibility to use OECTs in new biomedical fields well beyond their classical applications.Transistors multimodaux sensibles aux ions à polymères ambivalents pour biocapteurs hybridesCapteurs bio-électroniques intégrant l'algorithme des îlots pour le contrôle de la glycémie en boucle ouverte et fermé

Mechanosensor Channels in Mammalian Somatosensory Neurons

Mechanoreceptive sensory neurons innervating the skin, skeletal muscles andviscera signal both innocuous and noxious information necessary for proprioception, touchand pain. These neurons are responsible for the transduction of mechanical stimuli intoaction potentials that propagate to the central nervous system. The ability of these cells todetect mechanical stimuli impinging on them relies on the presence of mechanosensitivechannels that transduce the external mechanical forces into electrical and chemical signals.Although a great deal of information regarding the molecular and biophysical properties ofmechanosensitive channels in prokaryotes has been accumulated over the past two decades,less is known about the mechanosensitive channels necessary for proprioception and thesenses of touch and pain. This review summarizes the most pertinent data onmechanosensitive channels of mammalian somatosensory neurons, focusing on theirproperties, pharmacology and putative identity

Mécanismes moléculaires impliqués dans la détection des stimuli cutanés par les kératinocytes humains

Les kératinocytes épidermiques humains expriment le canal Cl- osmosensible VRAC. VRAC est inhibé par un irritant cutané de référence, l heptylamine. L hypotonicité diminue l inhibition de VRAC par l heptylamine, qui agit en s insérant dans la membrane plasmique. Des stimuli physico-chimiques comme les irritants, la bradykinine, l histamine, le menthol et les chocs mécaniques provoquent une mobilisation de Ca2+ dans les kératinocytes à partir du réticulum endoplasmique. Les stimuli mécaniques, l heptylamine et la bradykinine provoquent aussi une sécrétion Ca2+-indépendante d ATP par les kératinocytes. Cet ATP libéré participe à la réponse calcique en agissant de manière autocrine. Les stimuli cutanés agissent donc sur les kératinocytes en modulant les canaux ioniques, la [Ca2+]i et la libération d ATP qui est un acteur moléculaire essentiel de la communication kératinocytes-fibres sensorielles. Les kératinocytes seraient ainsi la caisse de résonance du système de détection sensorielle.AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocSudocFranceF

The amine-containing cutaneous irritant heptylamine inhibits the volume-regulated anion channel and mobilizes intracellular calcium in normal human epidermal keratinocytes.

Many amines are skin irritants and cause contact dermatitis. However, little is known about their mechanisms of action in keratinocytes except that they induce the release of the inflammatory mediators cytokines and ATP. Here, we tested whether volume-regulated anion channels (VRACs) in primary cultures of normal human epidermal keratinocytes are modulated by the referenced amine-containing cutaneous irritant heptylamine. Under isotonic conditions, we isolated the VRAC current (I(VRAC)) from other conductances using a high Ca(2+)-buffering internal solution. I(VRAC) ran up after patch rupturing and reached a plateau within 15 min. It was reversibly and dose-dependently inhibited by heptylamine with an IC(50) value of 260 muM. Cell-swelling caused by the application of a hypotonic solution increased 2.7-fold I(VRAC) and reduced the inhibition of VRAC by heptylamine with a dose-response curve shifted approximately 10-fold to the right. In addition, we showed, using cell-attached patch recordings, that adding heptylamine to the bath inhibited VRAC activity. This suggests that heptylamine diffuses into the membrane to inhibit VRAC. Finally, we demonstrated that heptylamine induced Ca(2+)-store depletion and that VRAC inhibition was not caused by the increase in cytosolic Ca(2+). Taken together, these results identify heptylamine as a blocker of VRAC and suggest that Ca(2+)-store depletion may be involved in mechanisms of irritant contact dermatitis caused by heptylamine

Cellules α et β du pancréas

Les diabètes sucrés sont des maladies métaboliques graves en constante augmentation. Ils sont dus à des déficits de sécrétion et d’action de l’insuline, la seule hormone qui diminue efficacement la glycémie. L’insuline est sécrétée par les cellules β des îlots pancréatiques. Les cellules α, également présentes dans les îlots, libèrent du glucagon et ont des effets opposés à ceux des cellules β sur la glycémie. Longtemps considérée comme néfaste dans le diabète, la cellule α apparaît désormais comme un modulateur des cellules β, ce qui nécessite de prendre désormais en compte cette cellule sur le plan thérapeutique. Cette revue présente le fonctionnement des cellules β et des cellules α. L’implication des interactions dynamiques entre ces deux types cellulaires dans l’homéostasie du glucose, mais aussi celle des autres nutriments, est également décrite

Nanoscale

Control of transport across membranes, whether natural or synthetic, is fundamental in many biotechnology applications, including sensing and drug release. Mutations of naturally existing protein channels, such as hemolysin, have been explored in the past. More recently, DNA channels with conductivities in the nanosiemens range have been designed. Regulating transport across DNA channels in response to external stimuli remains an important challenge. Previous designs relied on steric hindrance to control the inner diameter of the channel, which resulted in unstable electric signatures. In this paper we introduce a new design to control electric channel conductance of a DNA nanopore. The tensegrity driven mechanism inhibits the flux of small analytes while keeping a tightly controlled ionic transport modulated by the addition of specific DNA sequences. Current signals are clearly defined, with no sign of gating, opening new perspectives in single molecule DNA sensing

Differential beta cell coupling patterns drive biphasic activity

Background and aims: After food intake, pancreatic islets secrete insulin with a biphasic pattern, which is impaired in type 2 diabetic patients. The mechanisms underlying this pattern have not been fully elucidated and the presence of distinct vesicle pools has been proposed as explanation. Electrical activity of islets consists of individual β cell activity (action potentials, APs) and the multicellular electrical response due to coupling between β cells (slow potentials, SPs). We addressed here the contribution of these two distinct activities to the 1 st and the 2 nd phase of β cell activity, and their modulation by physiological concentrations of GLP-1. Materials and methods: Electrical activity (SPs and APs) of entire mice (C57Bl6/J, age 10-14 weeks) or human islets have been recorded on polymer-coated microelectrode arrays (MEA). These new electrodes allow simultaneous detection of APs (of very low amplitude) and SPs at a high time resolution (10'000 points/s x60 electrodes) for a prolonged period mimicking physiological digestion (2 h). Specific filters differentially detect SPs and APs and 3 parameters were analyzed at the same time: SP frequencies, SP amplitudes and AP frequencies. To investigate synchrony of SPs between different regions of the same islet, we used high density MEAs with an inter-electrode distance of 30 instead of 200 µm followed by analysis via Matlab. Results: Islets were stimulated with glucose concentrations in the physiological range (5.5-8.2 mM). Electrical responses were biphasic for both SPs and APs. APs were mainly present during the 1 st phase while the transition between the 1 st and the 2 nd phase is driven by SPs. In 2 nd phase, the SP amplitude and synchronisation increased significantly (1 st phase: 18.1±2.3 µV; 2 nd phase: 47.4±5.5 µV, p<0.0001), reflecting further electrical coupling and synchronisation of β cells. The intra-islet synchronisation was also further correlate using high density MEAs. The incretin GLP-1, at a physiological postprandial concentration (50 pM), did not change the individual activity of cells (APs) but increased specifically coupling (SPs) and only in the 2nd phase (37.7±3.0 µV vs 47.0±4.2 µV with GLP-1, p<0.0001). Furthermore, when GLP-1 was applied in the presence of a subthreshold glucose concentration (5.5 mM), the hormone triggered only a 2 nd phase. The biphasic electric profile was confirmed in human islets. Their exposure to a glucotoxic medium (20 mM glucose, 65 h) considerably increased basal activity and abolished the biphasic response as well as the discrimination between glucose concentrations. These glucotoxic effects were partially reversible. Conclusion: Our data show that (i) electrical activity pattern shape the biphasic secretion and (ii) the transition period between the 1 st and the 2 nd phase results from increasing electrical synchronisation. Thus biphasic secretion is primarily dictated by changes in electrical activity rather than vesicle pools. The effects of GLP-1 on only coupling SP signals and only during the 2 nd phase explain its clinical effects