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Nature Communications Apr 2024Fragile X syndrome (FXS) is an inherited form of intellectual disability caused by the loss of the mRNA-binding fragile X mental retardation protein (FMRP). FXS is...
Fragile X syndrome (FXS) is an inherited form of intellectual disability caused by the loss of the mRNA-binding fragile X mental retardation protein (FMRP). FXS is characterized by neuronal hyperexcitability and behavioral defects, however the mechanisms underlying these critical dysfunctions remain unclear. Here, using male Fmr1 knockout mouse model of FXS, we identify abnormal extracellular potassium homeostasis, along with impaired potassium channel Kir4.1 expression and function in astrocytes. Further, we reveal that Kir4.1 mRNA is a binding target of FMRP. Finally, we show that the deficit in astroglial Kir4.1 underlies neuronal hyperexcitability and several behavioral defects in Fmr1 knockout mice. Viral delivery of Kir4.1 channels specifically to hippocampal astrocytes from Fmr1 knockout mice indeed rescues normal astrocyte potassium uptake, neuronal excitability, and cognitive and social performance. Our findings uncover an important role for astrocyte dysfunction in the pathophysiology of FXS, and identify Kir4.1 channel as a potential therapeutic target for FXS.
Topics: Animals; Male; Mice; Astrocytes; Behavior, Animal; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Hippocampus; Mice, Inbred C57BL; Mice, Knockout; Neurons; Potassium; Potassium Channels, Inwardly Rectifying; RNA, Messenger
PubMed: 38678030
DOI: 10.1038/s41467-024-47681-y -
Biological Chemistry May 2024Fast and regulated potassium efflux by Slo1 channels is crucial in many tissues in animals including neurons, the kidney and smooth muscle. During the last decade,... (Review)
Review
Fast and regulated potassium efflux by Slo1 channels is crucial in many tissues in animals including neurons, the kidney and smooth muscle. During the last decade, structures have revealed many details about the gating mechanism and regulation of these large and complex molecular machines. This review summarizes these findings and the current knowledge about the intricate regulation of these important channels. Slo1 integrates sensing of the membrane potential via a voltage-sensor domain that undergoes subtle but significant structural rearrangements with a calcium-induced expansion of parts of the intracellular gating ring. Together, these two signals synergistically lead to changes in the conformation and chemical nature of the pore domain, allowing potassium ions to be translocated. In many native tissues, Slo1 channels are assembled with at least three classes of auxiliary subunits that change the gating kinetics or allow the channel to open also in absence of one of the two signals. Finally, Slo1 is inhibited, activated or deregulated by natural toxins and synthetic compounds, underlining the importance of the channel for the organism and as a potential target for drugs and other molecules.
PubMed: 38695343
DOI: 10.1515/hsz-2024-0037 -
Biophysical Journal Aug 2023Formation of the immunological synapse (IS) is a key event during initiation of an adaptive immune response to a specific antigen. During this process, a T cell and an...
Formation of the immunological synapse (IS) is a key event during initiation of an adaptive immune response to a specific antigen. During this process, a T cell and an antigen presenting cell form a stable contact that allows the T cell to integrate both internal and external stimuli in order to decide whether to activate. The threshold for T cell activation depends on the strength and frequency of the calcium (Ca) signaling induced by antigen recognition, and it must be tightly regulated to avoid undesired harm to healthy cells. Potassium (K) channels are recruited to the IS to maintain the negative membrane potential required to sustain Ca entry. However, the precise localization of K channels within the IS remains unknown. Here, we visualized the dynamic subsynaptic distribution of Kv1.3, the main voltage-gated potassium channel in human T cells. Upon T cell receptor engagement, Kv1.3 polarized toward the synaptic cleft and diffused throughout the F-actin rich distal compartment of the synaptic interface-an effect enhanced by CD2-CD58 corolla formation. As the synapse matured, Kv1.3 clusters were internalized at the center of the IS and released in extracellular vesicles. We propose a model in which specific distribution of Kv1.3 within the synapse indirectly regulates the channel function and that this process is limited through Kv1.3 internalization and release in extracellular vesicles.
PubMed: 37596785
DOI: 10.1016/j.bpj.2023.08.011 -
BioRxiv : the Preprint Server For... Aug 2023Healthy brains display a wide range of firing patterns, from synchronized oscillations during slowwave sleep to desynchronized firing during movement. These...
Healthy brains display a wide range of firing patterns, from synchronized oscillations during slowwave sleep to desynchronized firing during movement. These physiological activities coexist with periods of pathological hyperactivity in the epileptic brain, where neurons can fire in synchronized bursts. Most cortical neurons are pyramidal regular spiking cells (RS) with frequency adaptation and do not exhibit bursts in current-clamp experiments ( ). In this work, we investigate the transition mechanism of spike-to-burst patterns due to slow potassium and calcium currents, considering a conductance-based model of a cortical RS cell. The joint influence of potassium and calcium ion channels on high synchronous patterns is investigated for different synaptic couplings ( ) and external current inputs ( ). Our results suggest that slow potassium currents play an important role in the emergence of high-synchronous activities, as well as in the spike-to-burst firing pattern transitions. This transition is related to bistable dynamics of the neuronal network, where physiological asynchronous states coexist with pathological burst synchronization. The hysteresis curve of the coefficient of variation of the inter-spike interval demonstrates that a burst can be initiated by firing states with neuronal synchronization. Furthermore, we notice that high-threshold ( ) and low-threshold ( ) ion channels play a role in increasing and decreasing the parameter conditions ( and ) in which bistable dynamics occur, respectively. For high values of conductance, a synchronous burst appears when neurons are weakly coupled and receive more external input. On the other hand, when the conductance increases, higher coupling and lower are necessary to produce burst synchronization. In light of our results, we suggest that channel subtype-specific pharmacological interactions can be useful to induce transitions from pathological high bursting states to healthy states.
PubMed: 37645875
DOI: 10.1101/2023.08.16.553625 -
Developmental Biology Sep 2023Smoking cigarettes during pregnancy is associated with adverse effects on infants including low birth weight, defective lung development, and skeletal abnormalities....
Smoking cigarettes during pregnancy is associated with adverse effects on infants including low birth weight, defective lung development, and skeletal abnormalities. Pregnant women are increasingly turning to vaping [use of electronic (e)-cigarettes] as a perceived safer alternative to cigarettes. However, nicotine disrupts fetal development, suggesting that like cigarette smoking, nicotine vaping may be detrimental to the fetus. To test the impact of maternal vaping on fetal lung and skeletal development in mice, pregnant dams were exposed to e-cigarette vapor throughout gestation. At embryonic day (E)18.5, vape exposed litter sizes were reduced, and some embryos exhibited growth restriction compared to air exposed controls. Fetal lungs were collected for histology and whole transcriptome sequencing. Maternally nicotine vaped embryos exhibited histological and transcriptional changes consistent with impaired distal lung development. Embryonic lung gene expression changes mimicked transcriptional changes observed in adult mouse lungs exposed to cigarette smoke, suggesting that the developmental defects may be due to direct nicotine exposure. Fetal skeletons were analyzed for craniofacial and long bone lengths. Nicotine directly binds and inhibits the Kcnj2 potassium channel which is important for bone development. The length of the maxilla, palatal shelves, humerus, and femur were reduced in vaped embryos, which was further exacerbated by loss of one copy of the Kcnj2 gene. Nicotine vapor exposed Kcnj2 embryos also had significantly lower birth weights than unexposed animals of either genotype. Kcnj2 mutants had severely defective lungs with and without vape exposure, suggesting that potassium channels may be broadly involved in mediating the detrimental developmental effects of nicotine vaping. These data indicate that intrauterine nicotine exposure disrupts fetal lung and skeletal development likely through inhibition of Kcnj2.
Topics: Female; Pregnancy; Animals; Humans; Mice; Vaping; Nicotine; Electronic Nicotine Delivery Systems; Lung; E-Cigarette Vapor
PubMed: 37353105
DOI: 10.1016/j.ydbio.2023.06.002 -
Circulation. Arrhythmia and... Sep 2023Hypoxia-ischemia predisposes to atrial arrhythmia. Atrial ATP-sensitive potassium channel (K) modulation during hypoxia has not been explored. We investigated the...
BACKGROUND
Hypoxia-ischemia predisposes to atrial arrhythmia. Atrial ATP-sensitive potassium channel (K) modulation during hypoxia has not been explored. We investigated the effects of hypoxia on atrial electrophysiology in mice with global deletion of K pore-forming subunits.
METHODS
Whole heart K RNA expression was probed. Whole-cell K current and action potentials were recorded in isolated wild-type (WT), Kir6.1 global knockout (6.1-gKO), and Kir6.2 global knockout (6.2-gKO) murine atrial myocytes. Langendorff-perfused hearts were assessed for atrial effective refractory period (ERP), conduction velocity, wavefront path length (WFPL), and arrhymogenicity under normoxia/hypoxia using a microelectrode array and programmed electrical stimulation. Heart histology was assessed.
RESULTS
Expression patterns were essentially identical for all K subunit RNA across human heart, whereas in mouse, Kir6.1 and SUR2 (sulphonylurea receptor subunit) were higher in ventricle than atrium, and Kir6.2 and SUR1 were higher in atrium. Compared with WT, 6.2-gKO atrial myocytes had reduced tolbutamide-sensitive current and action potentials were more depolarized with slower upstroke and reduced peak amplitude. Action potential duration was prolonged in 6.1-gKO atrial myocytes, absent of changes in other ion channel gene expression or atrial myocyte hypertrophy. In Langendorff-perfused hearts, baseline atrial ERP was prolonged and conduction velocity reduced in both K knockout mice compared with WT, without histological fibrosis. Compared with baseline, hypoxia led to conduction velocity slowing, stable ERP, and WFPL shortening in WT and 6.1-gKO hearts, whereas WFPL was stable in 6.2-gKO hearts due to ERP prolongation with conduction velocity slowing. Tolbutamide reversed hypoxia-induced WFPL shortening in WT and 6.1-gKO hearts through ERP prolongation. Atrial tachyarrhythmias inducible with programmed electrical stimulation during hypoxia in WT and 6.1-gKO mice correlated with WFPL shortening. Spontaneous arrhythmia was not seen.
CONCLUSIONS
K block/absence leads to cellular and tissue level atrial electrophysiological modification. Kir6.2 global knockout prevents hypoxia-induced atrial WFPL shortening and atrial arrhythmogenicity to programmed electrical stimulation. This mechanism could be explored translationally to treat ischemically driven atrial arrhythmia.
Topics: Humans; Animals; Mice; KATP Channels; Atrial Fibrillation; Tolbutamide; Tachycardia; Heart Atria; Hypoxia; Adenosine Triphosphate
PubMed: 37646176
DOI: 10.1161/CIRCEP.123.011870 -
Cellular and Molecular Life Sciences :... Nov 2023Mutations of large conductance Ca- and voltage-activated K channels (BK) are associated with cognitive impairment. Here we report that CA1 pyramidal neuron-specific...
Mutations of large conductance Ca- and voltage-activated K channels (BK) are associated with cognitive impairment. Here we report that CA1 pyramidal neuron-specific conditional BK knock-out (cKO) mice display normal locomotor and anxiety behavior. They do, however, exhibit impaired memory acquisition and retrieval in the Morris Water Maze (MWM) when compared to littermate controls (CTRL). In line with cognitive impairment in vivo, electrical and chemical long-term potentiation (LTP) in cKO brain slices were impaired in vitro. We further used a genetically encoded fluorescent K biosensor and a Ca-sensitive probe to observe cultured hippocampal neurons during chemical LTP (cLTP) induction. cLTP massively reduced intracellular K concentration ([K]) while elevating L-Type Ca channel- and NMDA receptor-dependent Ca oscillation frequencies. Both, [K] decrease and Ca oscillation frequency increase were absent after pharmacological BK inhibition or in cells lacking BK. Our data suggest that L-Type- and NMDAR-dependent BK-mediated K outflow significantly contributes to hippocampal LTP, as well as learning and memory.
Topics: Mice; Animals; Long-Term Potentiation; Large-Conductance Calcium-Activated Potassium Channels; Neuronal Plasticity; Hippocampus; Neurons; Mice, Knockout
PubMed: 37989805
DOI: 10.1007/s00018-023-05016-y -
International Journal of Molecular... Apr 2024Ionic channels are present in eucaryotic plasma and intracellular membranes. They coordinate and control several functions. Potassium channels belong to the most diverse... (Review)
Review
Ionic channels are present in eucaryotic plasma and intracellular membranes. They coordinate and control several functions. Potassium channels belong to the most diverse family of ionic channels that includes ATP-dependent potassium (KATP) channels in the potassium rectifier channel subfamily. These channels were initially described in heart muscle and then in other tissues such as pancreatic, skeletal muscle, brain, and vascular and non-vascular smooth muscle tissues. In pancreatic beta cells, KATP channels are primarily responsible for maintaining the membrane potential and for depolarization-mediated insulin release, and their decreased density and activity may be related to insulin resistance. KATP channels' relationship with insulin resistance is beginning to be explored in extra-pancreatic beta tissues like the skeletal muscle, where KATP channels are involved in insulin-dependent glucose recapture and their activation may lead to insulin resistance. In adipose tissues, KATP channels containing Kir6.2 protein subunits could be related to the increase in free fatty acids and insulin resistance; therefore, pathological processes that promote prolonged adipocyte KATP channel inhibition might lead to obesity due to insulin resistance. In the central nervous system, KATP channel activation can regulate peripheric glycemia and lead to brain insulin resistance, an early peripheral alteration that can lead to the development of pathologies such as obesity and Type 2 Diabetes Mellitus (T2DM). In this review, we aim to discuss the characteristics of KATP channels, their relationship with clinical disorders, and their mechanisms and potential associations with peripheral and central insulin resistance.
Topics: Humans; Potassium Channels; Insulin Resistance; Diabetes Mellitus, Type 2; Insulin; Insulin, Regular, Human; Pancreatic Hormones; KATP Channels; Obesity; Potassium; Adenosine Triphosphate
PubMed: 38612888
DOI: 10.3390/ijms25074079 -
International Journal of Molecular... Jan 2024The Gárdos channel (KCNN4) and Piezo1 are the best-known ion channels in the red blood cell (RBC) membrane. Nevertheless, the quantitative electrophysiological behavior...
The Gárdos channel (KCNN4) and Piezo1 are the best-known ion channels in the red blood cell (RBC) membrane. Nevertheless, the quantitative electrophysiological behavior of RBCs and its heterogeneity are still not completely understood. Here, we use state-of-the-art biochemical methods to probe for the abundance of the channels in RBCs. Furthermore, we utilize automated patch clamp, based on planar chips, to compare the activity of the two channels in reticulocytes and mature RBCs. In addition to this characterization, we performed membrane potential measurements to demonstrate the effect of channel activity and interplay on the RBC properties. Both the Gárdos channel and Piezo1, albeit their average copy number of activatable channels per cell is in the single-digit range, can be detected through transcriptome analysis of reticulocytes. Proteomics analysis of reticulocytes and mature RBCs could only detect Piezo1 but not the Gárdos channel. Furthermore, they can be reliably measured in the whole-cell configuration of the patch clamp method. While for the Gárdos channel, the activity in terms of ion currents is higher in reticulocytes compared to mature RBCs, for Piezo1, the tendency is the opposite. While the interplay between Piezo1 and Gárdos channel cannot be followed using the patch clamp measurements, it could be proved based on membrane potential measurements in populations of intact RBCs. We discuss the Gárdos channel and Piezo1 abundance, interdependencies and interactions in the context of their proposed physiological and pathophysiological functions, which are the passing of small constrictions, e.g., in the spleen, and their active participation in blood clot formation and thrombosis.
Topics: Biological Transport; Calcium; Erythrocytes; Reticulocytes; Humans; Intermediate-Conductance Calcium-Activated Potassium Channels; Ion Channels
PubMed: 38338693
DOI: 10.3390/ijms25031416 -
BioRxiv : the Preprint Server For... Oct 2023The plasma membrane is a well-organized structure of lipids and proteins, segmented into lipid compartments under 200 nm in size. This specific spatial patterning is...
The plasma membrane is a well-organized structure of lipids and proteins, segmented into lipid compartments under 200 nm in size. This specific spatial patterning is crucial for the function of proteins and necessitates super-resolution imaging for its elucidation. Here, we establish that the genetically encoded enhanced green fluorescent protein (EGFP), when combined with direct optical reconstruction microscopy (dSTORM), tracks shear- and cholesterol-induced nanoscopic patterning of potassium channels overexpressed in HEK293T cells. Leveraging EGFP in dSTORM (EGFP-STORM), our findings indicate that cholesterol directs the C-terminus of TWIK-related potassium channel (TREK-1) to ceramide-enriched lipid ganglioside (GM1) clusters. In the absence of the C-terminus, the channel associates with phosphatidylinositol 4,5-bisphosphate (PIP) cluster. Similarly, cholesterol derived from astrocytes repositions EGFP-tagged inward-rectifying potassium (Kir) channels into GM1 clusters. Without cholesterol, the channel aligns with PIP lipids. We deduce that cholesterol's interaction with Kir sequesters the channel, separating it from its activating lipid PIP. Fundamentally, a genetically encoded EGFP tag should make any protein amenable to dSTORM analysis.
PubMed: 37873307
DOI: 10.1101/2023.10.13.561998