Whilst the phenomenon of an electrical resting membrane potential (RMP) is a central tenet of biology, it is nearly always discussed as a phenomenon that facilitates the propagation of action ...potentials in excitable tissue, muscle, and nerve. However, as ion channel research shifts beyond these tissues, it became clear that the RMP is a feature of virtually all cells studied. The RMP is maintained by the cell's compliment of ion channels. Transcriptome sequencing is increasingly revealing that equally rich compliments of ion channels exist in both excitable and non-excitable tissue. In this review, we discuss a range of critical roles that the RMP has in a variety of cell types beyond the action potential. Whereas most biologists would perceive that the RMP is
about excitability, the data show that in fact excitability is only a small part of it. Emerging evidence show that a dynamic membrane potential is critical for many other processes including cell cycle, cell-volume control, proliferation, muscle contraction (even in the absence of an action potential), and wound healing. Modulation of the RMP is therefore a potential target for many new drugs targeting a range of diseases and biological functions from cancer through to wound healing and is likely to be key to the development of successful stem cell therapies.
Microglia, the resident immune cells in the brain, survey the environment of the healthy brain. Microglial migration is essential for many physiological and pathophysiological processes. Although ...microglia express some members of the transient receptor potential (TRP) channel family, there is little knowledge regarding the physiological roles of TRP channels in microglia. Here, we explored the role of TRP vanilloid 1 (TRPV1), a channel opened by capsaicin, heat, protons, and endovanilloids, in microglia. We found that application of capsaicin induced concentration‐dependent migration in microglia derived from wild‐type mice but not in those derived from TRPV1 knockout (TRPV1‐KO) mice. Capsaicin‐induced microglial migration was significantly inhibited by co‐application of the TRPV1 blocker SB366791 and the Ca2+ chelator BAPTA‐AM. Using RT‐PCR and immunocytochemistry, we validated that TRPV1 was expressed in microglia. Electrophysiological recording, intracellular Ca2+ imaging, and immunocytochemistry indicated that TRPV1 was localized primarily in intracellular organelles. Treatment with capsaicin induced an increase in intramitochondrial Ca2+ concentrations and mitochondrial depolarization. Furthermore, microglia derived from TRPV1‐KO mice showed delayed Ca2+ efflux compared with microglia derived from wild‐type mice. Capsaicin‐induced microglial migration was inhibited by membrane‐permeable antioxidants and MAPK inhibitors, suggesting that mitochondrial TRPV1 activation induced Ca2+‐dependent production of ROS followed by MAPK activation, which correlated with an augmented migration of microglia. Moreover, a mixture of three endovanilloids augmented microglial migration via TRPV1 activation. Together, these results indicate that mitochondrial TRPV1 plays an important role in inducing microglial migration. Activation of TRPV1 triggers an increase in intramitochondrial Ca2+ concentration and following depolarization of mitochondria, which results in mtROS production, MAPK activation, and enhancement of chemotactic activity in microglia. GLIA 2015;63:1870–1882
Main Points
Activation of TRPV1 triggers an increase i Main points; n intramitochondrial Ca2+ concentration and following depolarization of mitochondria, which results in mtROS production, MAPK activation, and enhancement of chemotactic activity in microglia.
Despite being the most abundant synaptic vesicle membrane protein, the function of synaptophysin remains enigmatic. For example, synaptic transmission was reported to be completely normal in ...synaptophysin knockout mice; however, direct experiments to monitor the synaptic vesicle cycle have not been carried out. Here, using optical imaging and electrophysiological experiments, we demonstrate that synaptophysin is required for kinetically efficient endocytosis of synaptic vesicles in cultured hippocampal neurons. Truncation analysis revealed that distinct structural elements of synaptophysin differentially regulate vesicle retrieval during and after stimulation. Thus, synaptophysin regulates at least two phases of endocytosis to ensure vesicle availability during and after sustained neuronal activity.
Focused ultrasound is a promising noninvasive technology for neural stimulation. Here we use the isolated salamander retina to characterize the effect of ultrasound on an intact neural circuit and ...compared these effects with those of visual stimulation of the same retinal ganglion cells. Ultrasound stimuli at an acoustic frequency of 43 MHz and a focal spot diameter of 90 μm delivered from a piezoelectric transducer evoked stable responses with a temporal precision equal to strong visual responses but with shorter latency. By presenting ultrasound and visual stimulation together, we found that ultrasonic stimulation rapidly modulated visual sensitivity but did not change visual temporal filtering. By combining pharmacology with ultrasound stimulation, we found that ultrasound did not directly activate retinal ganglion cells but did in part activate interneurons beyond photoreceptors. These results suggest that, under conditions of strong localized stimulation, timing variability is largely influenced by cells beyond photoreceptors. We conclude that ultrasonic stimulation is an effective and spatiotemporally precise method to activate the retina. Because the retina is the most accessible part of the CNS in vivo, ultrasonic stimulation may have diagnostic potential to probe remaining retinal function in cases of photoreceptor degeneration, and therapeutic potential for use in a retinal prosthesis. In addition, because of its noninvasive properties and spatiotemporal resolution, ultrasound neurostimulation promises to be a useful tool to understand dynamic activity in pharmacologically defined neural pathways in the retina.
Biochar-based compound fertilizers (BCF) and amendments have proven to enhance crop yields and modify soil properties (pH, nutrients, organic matter, structure etc.) and are now in commercial ...production in China. While there is a good understanding of the changes in soil properties following biochar addition, the interactions within the rhizosphere remain largely unstudied, with benefits to yield observed beyond the changes in soil properties alone. We investigated the rhizosphere interactions following the addition of an activated wheat straw BCF at an application rates of 0.25% (g·g−1 soil), which could potentially explain the increase of plant biomass (by 67%), herbage N (by 40%) and P (by 46%) uptake in the rice plants grown in the BCF-treated soil, compared to the rice plants grown in the soil with conventional fertilizer alone. Examination of the roots revealed that micron and submicron-sized biochar were embedded in the plaque layer. BCF increased soil Eh by 85 mV and increased the potential difference between the rhizosphere soil and the root membrane by 65 mV. This increased potential difference lowered the free energy required for root nutrient accumulation, potentially explaining greater plant nutrient content and biomass. We also demonstrate an increased abundance of plant-growth promoting bacteria and fungi in the rhizosphere. We suggest that the redox properties of the biochar cause major changes in electron status of rhizosphere soils that drive the observed agronomic benefits.
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•Biochar-based fertilizer (BCF) is known to enhance crop yields and soil properties.•Wheat straw BCF was applied to the soil to investigate rhizosphere interactions.•There was an increase in rice yield, and N (40%), P (46%), Mg, K and Na uptakes.•Micron and submicron-sized biochar were embedded in the plaque layer.•Biochar increased soil Eh, which resulted in greater plant nutrient content.
As animals navigate, they must identify features within context. In the mammalian brain, the hippocampus has the ability to separately encode different environmental contexts, even when they share ...some prominent features. To do so, neurons respond to sensory features in a context-dependent manner; however, it is not known how this encoding emerges. To examine this, we performed electrical recordings in the hippocampus as mice navigated in two distinct virtual environments. In CA1, both synaptic input to single neurons and population activity strongly tracked visual cues in one environment, whereas responses were almost completely absent when the same cue was presented in a second environment. A very similar, highly context-dependent pattern of cue-driven spiking was also observed in CA3. These results indicate that CA1 inherits a complex spatial code from upstream regions, including CA3, that have already computed a context-dependent representation of environmental features.
Hybrid interfaces between organic semiconductors and living tissues represent a new tool for in-vitro and in-vivo applications, bearing a huge potential, from basic researches to clinical ...applications. In particular, light sensitive conjugated polymers can be exploited as a new approach for optical modulation of cellular activity. In this work we focus on light-induced changes in the membrane potential of Human Embryonic Kidney (HEK-293) cells grown on top of a poly(3-hexylthiophene) (P3HT) thin film. On top of a capacitive charging of the polymer interface, we identify and fully characterize two concomitant mechanisms, leading to membrane depolarization and hyperpolarisation, both mediated by a thermal effect. Our results can be usefully exploited in the creation of a new platform for light-controlled cell manipulation, with possible applications in neuroscience and medicine.
Neocortical activity can evoke sensory percepts, but the cellular mechanisms remain poorly understood. We trained mice to detect single brief whisker stimuli and report perceived stimuli by licking ...to obtain a reward. Pharmacological inactivation and optogenetic stimulation demonstrated a causal role for the primary somatosensory barrel cortex. Whole-cell recordings from barrel cortex neurons revealed membrane potential correlates of sensory perception. Sensory responses depended strongly on prestimulus cortical state, but both slow-wave and desynchronized cortical states were compatible with task performance. Whisker deflection evoked an early (<50 ms) reliable sensory response that was encoded through cell-specific reversal potentials. A secondary late (50-400 ms) depolarization was enhanced on hit trials compared to misses. Optogenetic inactivation revealed a causal role for late excitation. Our data reveal dynamic processing in the sensory cortex during task performance, with an early sensory response reliably encoding the stimulus and later secondary activity contributing to driving the subjective percept.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The sodium leak channel NALCN is a key player in establishing the resting membrane potential (RMP) in neurons and transduces changes in extracellular Ca
concentration (Ca
) into increased neuronal ...excitability as the downstream effector of calcium-sensing receptor (CaSR). Gain-of-function mutations in the human NALCN gene cause encephalopathy and severe intellectual disability. Thus, understanding the regulatory mechanisms of NALCN is important for both basic and translational research. This study reveals a novel mechanism for NALCN regulation by arginine methylation. Hippocampal dentate granule cells in protein arginine methyltransferase 7 (PRMT7)-deficient mice display a depolarization of the RMP, decreased threshold currents, and increased excitability compared to wild-type neurons. Electrophysiological studies combined with molecular analysis indicate that enhanced NALCN activities contribute to hyperexcitability in PRMT7-/- neurons. PRMT7 depletion in HEK293T cells increases NALCN activity by shifting the dose-response curve of NALCN inhibition by Ca
without affecting NALCN protein levels. In vitro methylation studies show that PRMT7 methylates a highly conserved Arg1653 of the NALCN gene located in the carboxy-terminal region that is implicated in CaSR-mediated regulation. A kinase-specific phosphorylation site prediction program shows that the adjacent Ser1652 is a potential phosphorylation site. Consistently, our data from site-specific mutants and PKC inhibitors suggest that Arg1653 methylation might modulate Ser1652 phosphorylation mediated by CaSR/PKC-delta, leading to Ca
-mediated NALCN suppression. Collectively, these data suggest that PRMT7 deficiency decreases NALCN methylation at Arg1653, which, in turn, decreases CaSR/PKC-mediated Ser1652 phosphorylation, lifting NALCN inhibition, thereby enhancing neuronal excitability. Thus, PRMT7-mediated NALCN inhibition provides a potential target for the development of therapeutic tools for neurological diseases.
Mitochondrial membrane potential (MMP) and sulfur dioxide (SO
) significantly affect the mitochondrial state. In this work,
and
were constructed through side-chain engineering, in which
bearing the ...poorer hydrophobicity could localize on mitochondria better. Interestingly, short-wave emission was captured due to the sensitive response of
to SO
(LOD = 13.8 nM). Meanwhile, the probe could bind with DNA, presenting enhanced long-wave emission. Encouragingly,
could migrate from mitochondria to the nucleus when MMP was decreased, accompanied by the increase of fluorescence lifetime (9-fold). Hence,
could be used for dual-channel monitoring of mitochondrial SO
and MMP, which showed a completely different pathway from the commercial MMP detectors JC-1/JC-10. The cellular experiments showed that MMP was gradually decreased due to reactive oxygen species-triggered oxidative stress, and the SO
level was up-regulated simultaneously. Overall, this work proposed a new method to investigate and diagnose the mitochondrial-related diseases.
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