Search Results (116)

Epilepsy is a neurological disorder characterized by a long-lasting predisposition to recurrently generate unprovoked seizures. Epilepsy affects over 70 million people worldwide, with approximately one-third suffering from pharmacoresistant seizures. Currently, the clinical antiseizure drugs lack efficacy in preventing epileptogenesis. Adenosine, as an endogenous anticonvulsant, inhibits the development of epilepsy via interaction with the molecular epileptogenic network on several levels: (i) Activation of A1 receptor inhibits glutamate release via presynaptic inhibition, and hyperpolarizes the synaptic potentials in postsynaptic neurons. (ii) The A2A receptor on astrocytes interacts with astroglial glutamate transporter GLT-1, controlling glial glutamate homeostasis. (iii) Activation of the A3 receptor inhibits GABA transporter type 1-mediated GABA uptake. (iv) Adenosine kinase (ADK) is highlighted as a pathological hallmark of epilepsy, with its distinct isoforms driving different mechanisms. The cytoplasmic short isoform (ADK-S) in astrocytes controls extracellular adenosine and receptor-mediated pathways, whereas the nuclear long isoform (ADK-L) in astrocytes and specific neurons regulates epigenetic mechanisms without relying on adenosine receptors. Collectively, this review clarifies the adenosine system’s critical regulatory role in the epileptogenic network, highlights adenosine receptors and ADK isoforms as promising therapeutic targets for epilepsy, and provides a theoretical basis for developing novel disease-modifying therapies for pharmacoresistant epilepsy while laying a foundation for subsequent preclinical and clinical translation. Full article

The “athlete’s heart” phenotype, featuring resting bradycardia, has traditionally been viewed as a benign adaptation. However, emerging evidence associates prolonged, high-intensity endurance training with an increased risk of clinical sinoatrial node dysfunction. This systematic review synthesizes evidence on exercise-induced intrinsic Sinoatrial Node (SAN) electrophysiological remodelling and evaluates its dual nature along the adaptation–pathology continuum. Following PRISMA guidelines, a systematic search of PubMed, Web of Science, and Google Scholar (2000–2025) identified 17 eligible studies. Analysis revealed that in humans, rodents, and rabbits, exercise induces intrinsic SAN electrophysiological remodelling—a “membrane clock” reset characterized by coordinated downregulation of pacemaker currents, notably Hyperpolarization-activated cyclic nucleotide-gated cation channel (I_f), via the Nkx2.5-miR-423-5p transcription factor pathway. Evidence for “calcium clock” involvement remains inconsistent. In contrast, large animal models (e.g., dogs, horses) show only parasympathetic-mediated bradycardia without intrinsic remodelling. Training loads may induce structural changes (e.g., fibrosis), providing an anatomical substrate for pathology. Moderating factors such as training type and ageing contribute to a phenotype of “acquired SAN reserve reduction. Exercise-induced intrinsic SAN remodelling is a physiological adaptation mechanism that, under certain conditions, can cross a threshold to become a pathological cause of clinical dysfunction. Recognizing this continuum is essential for risk stratification and future therapeutic innovation. Full article

QX-314 is a positively charged lidocaine derivative with the membrane-impermeant property. This compound applied at the intracellular side has been shown to suppress the voltage-gated Na⁺ current (I_Na), while lidocaine itself acts to suppress the hyperpolarization-activated cation current (I_h). To what extent this drug may exert any effects on various plasmalemmal ionic currents still remains largely unknown. This investigation focused on the impact of QX-314 on ionic currents in GH₃ cells derived from pituitary tumors. This compound applied extracellularly was noted to differentially suppress the amplitude of transient and late I_Na with an IC₅₀ value of 93 and 42 μM, respectively. In GH₃ cells dialyzed with QX-314 (10 μM), the I_Na(T) amplitude evoked by a brief depolarizing step was decreased, and its inactivation was increased. Moreover, QX-314, when applied extracellularly at 100 μM, diminished the amplitude of the I_h current with an IC₅₀ of 68 μM. Intracellular dialysis with QX-314 also suppressed I_h amplitude; moreover, the later application of oxaliplatin reversed this suppression. As cells were extracellularly and continually exposed to QX-314, the magnitude of the erg-mediated K⁺ current (I_K(erg)) was also effectively suppressed with an IC₅₀ value of 73 μM. Furthermore, upon intracellular dialysis with QX-314 (10 μM), the degree of the voltage-dependent hysteresis (Hys_(V)) of I_K(erg) during the long-lasting isosceles-triangular ramp voltage was decreased; during continued exposure to QX-314, further extracellular bath additions of PD118057 (10 μM) counteracted QX-314-induced suppression. However, the extracellular addition of QX-314 (100 μM) mildly suppressed the outward delayed rectifier K⁺ current in GH₃ cells. Collectively, QX-314 effectively suppressed I_Na, I_h, and I_K(erg) in GH₃ cells, a model of endocrine function, and these actions may contribute to their physiological functions, if similar effects are observed in vivo. Full article

The GABA_A receptors, through a short-term interaction with a mediator, induce hyperpolarization of the membrane potential (V_m) via the passive influx of chloride ions (Cl⁻) into neurons. The massive (or intense) activation of the GABA_ARs by the agonist could potentially lead to depolarization/excitation of the V_m. Although the ionic mechanisms of GABA_A-mediated depolarization remain incompletely understood, a combination of the outward chloride current and the inward bicarbonate current and the resulting pH shift are the main reasons for this event. The GABA_A responses are determined by the ionic gradients—neuronal pH/bicarbonate homeostasis is maintained by carbonic anhydrase and electroneutral/electrogenic bicarbonate transporters and the chloride level is maintained by secondary active cation–chloride cotransporters. Massive activation can also induce the rundown effect of the receptor function. This rundown effect partly involves phosphorylation, Ca²⁺ and the processes of receptor desensitization. In addition, by various methods (including fluorescence and optical genetic methods), it has been shown that massive activation of GABA_ARs during pathophysiological activity is also associated with an increase in [Cl⁻]_i and a decline in the pH and ATP levels in neurons. Although the relationship between the neuronal changes induced by massive activation of GABAergic signaling and the risk of developing neurodegenerative disease has been extensively studied, the molecular determinants of this process remain somewhat mysterious. The aim of this review is to summarize the data on the relationship between the massive activation of inhibitory signaling and the ionic changes in neurons. The potential role of receptor dysfunction during massive activation and the resulting ionic and metabolic disruption in neurons during the manifestation of network/seizure activity will be considered. Full article

Cardioprotection against ischemia is achieved using openers of mitochondrial ATP-sensitive K⁺ (mitoKATP) channels such as diazoxide (DZX), leading to pharmacological preconditioning (PPC). We previously reported that PPC decreases the abundance of ventricular Cav1.2 channels, but PPC’s effects on other channels remain largely unexplored. In this study, we hypothesized that DZX regulates the expression of hyperpolarization-activated cyclic nucleotide potassium channel 4 (HCN4) channels in sinoatrial node cells (SANCs), the specialized cardiomyocytes that generate the heartbeat. DZX increased the heart rate in intact adult rats. Patch-clamp experiments revealed an increase in the magnitude of ionic currents through HCN4 channels, which was abolished by the reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC) and the selective mitoKATP channel inhibitor 5-hydroxydecanoate (5-HD). Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and Western blot assays showed that DZX increased HCN4 channel expression at the mRNA and protein levels. Immunofluorescence analyses revealed that PPC increased HCN4 fluorescence, which was abolished by NAC. DZX increased nuclear translocation of c-Fos and decreased protein abundance of RE1 silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF), suggesting the involvement of these factors. Our results suggest that PPC increases the heart rate by upregulating HCN4 channel expression through a mechanism involving c-Fos, REST, and ROS. Full article

Pituitary cells are specialized cells located within the pituitary gland, a small, pea-sized gland situated at the base of the brain. Through the use of cellular electrophysiological techniques, the electrical properties of these cells have been revealed. This review paper aims to introduce the ion currents that are known to be functionally expressed in pituitary cells. These currents include a voltage-gated Na⁺ current (I_Na), erg-mediated K⁺ current (I_K(erg)), M-type K⁺ current (I_K(M)), hyperpolarization-activated cation current (I_h), and large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel. The biophysical characteristics of the respective ion current were described. Additionally, we also provide explanations for the effect of various drugs or compounds on each of these currents. GH₃-cell exposure to GV-58 can increase the magnitude of I_Na with a concurrent rise in the inactivation time constant of the current. The presence of esaxerenone, an antagonist of the aldosterone receptor, directly suppresses the magnitude of peak and late I_Na. Risperidone, an atypical antipsychotic agent, is effective at suppressing the I_K(erg) amplitude directly, and di(2-ethylhexyl)-phthalate suppressed I_K(erg). Solifenacin and kynurenic acid can interact with the K_M channel to stimulate I_K(M), while carisbamate and cannabidiol inhibit the I_h amplitude activated by sustained hyperpolarization. Moreover, the presence of either rufinamide or QO-40 can enhance the activity of single BK_Ca channels. To summarize, alterations in ion currents within native pituitary cells or pituitary tumor cells can influence their functional activity, particularly in processes like stimulus–secretion coupling. The effects of small-molecule modulators, as demonstrated here, bear significance in clinical, therapeutic, and toxicological contexts. Full article

Background: Dorsal raphe serotonin (5-hydroxytryptamine, 5-HT) neurons are spontaneously active and release 5-HT that is critical for normal brain function and regulates mood and emotion. Serotonin reuptake inhibitors (SSRIs) increase the synaptic and extracellular 5-HT level and are effective in treating depression. Treatment of two weeks or longer is often required for SSRIs to produce clinical benefits. The cellular mechanism underlying this delay is not fully understood. Methods and Results: Using whole-cell patch clamp recording in brain slices, here we show that the GABAergic inputs inhibit the spike firing of raphe 5-HT neurons. This GABAergic regulation was reduced by 5-HT; additionally, this 5-HT effect was prevented by the G-protein-activated inwardly rectifying potassium (GirK) channel inhibitor tertiapin-Q, indicating a contribution of 5-HT activation of GirK channels in GABAergic presynaptic axon terminals. Equally important, after 14 days of treatment with fluoxetine, a widely used SSRI type antidepressant, the 5-HT inhibition of GABAergic inputs was downregulated. Furthermore, chronic fluoxetine treatment downregulated the 5-HT activation of the inhibitory GirK current in 5-HT neurons. Conclusions: Taken together, our results suggest that chronic fluoxetine treatment, by blocking 5-HT reuptake and hence increasing the extracellular 5-HT level, can downregulate the function of 5-HT1B receptors on the GABAergic afferent axon terminals synapsing onto 5-HT neurons, allowing extrinsic GABAergic neurons to more effectively influence 5-HT neurons; simultaneously, chronic fluoxetine treatment also downregulated somatic 5-HT autoreceptor-activated GirK channel-mediated hyperpolarization and decrease in input resistance, rendering 5-HT neurons resistant to autoinhibition and leading to increased 5-HT neuron activity. These neuroplastic changes in raphe 5-HT neurons and their GABAergic afferents may contribute to the behavioral effect of SSRIs. Full article

The sigma-1 receptor (Sig-1R) has emerged as a significant target in the realm of pain management and has been the subject of extensive research. Nonetheless, its specific function in inflammatory pain within dorsal root ganglion (DRG) neurons remains inadequately elucidated. This study utilized whole-cell patch clamp techniques, single-cell real-time PCR, and immunohistochemistry to examine the influence of Sig-1R on inflammatory pain induced by complete Freund’s adjuvant (CFA) in a rat model. Our results revealed several key findings: (1) The expression of Sig-1R was found to be upregulated during the progression of inflammatory pain, with a notable translocation from the cytoplasm to the membrane; (2) Inhibition of peripheral Sig-1R using S1RA resulted in a reduction of CFA-induced allodynia; (3) Activation of Sig-1R through PRE-084 led to a decrease in the fast sodium current in isolated DRG neurons from CFA-treated rats, which was associated with a diminished action potential (AP) peak and maximum depolarizing rate (MDR), as well as an increased rheobase; (4) Furthermore, PRE-084 was observed to enhance the slow component of the sodium current, resulting in hyperpolarization of the threshold potential and an increase in AP firing frequency, alongside an elevation in the mRNA expression of the slow sodium channel Nav1.9 in CFA-treated rats. In conclusion, our findings suggest that the modulation of sodium channels by Sig-1R in DRG neurons plays a significant role in the mechanisms underlying inflammatory pain. Full article

Background: Small conductance Ca²⁺ activated K⁺ channels (K_Ca2.3) are important regulators of vascular function. They provide Ca²⁺-dependent hyperpolarization of the endothelial membrane potential, promoting agonist-induced vasodilation. Another important mechanism of influence may occur through positive feedback regulation of endothelial Ca²⁺ signals, likely via amplification of influx through membrane cation channels. K_Ca2.3 channels have recently been implicated in flow-mediated dilation of the arterial vasculature and may contribute to the crucial homeostatic role of shear stress in preventing vascular wall remodeling and progressive vascular disease (i.e., atherosclerosis). The impact of K_Ca2.3 channels on endothelial Ca²⁺ signaling under physiologically relevant shear stress conditions remains unknown. Methods: In the current study, we employ mice expressing an endothelium-specific Ca²⁺ fluorophore (cdh5-GCaMP8) to characterize the K_Ca2.3 channel influence on the dynamic Ca²⁺ signaling profile along the arterial endothelium in the presence and absence of shear-stress. Results: Our data indicate K_Ca2.3 channels have a minimal influence on basal Ca²⁺ signaling in the carotid artery endothelium in the absence of flow, but they contribute substantially to amplification of Ca²⁺ dynamics in the presence of flow and their influence can be augmented through exogenous positive modulation. Conclusions: The findings suggest a pivotal role for K_Ca2.3 channels in adjusting the profile of homeostatic dynamic Ca²⁺ signals along the arterial intima under flow. Full article

In vitro experiments performed on dissociated dorsal root ganglion (DRG) neurons suggest the involvement of the hyperpolarization-activated cation current (I_h) in enhancing neuronal excitability, potentially contributing to neuropathic pain. However, the more confirmative in vivo information about how nerve injury interacts with I_h is lacking. In this study, I_h was recorded in vivo using the dynamic single-electrode voltage clamp (dSEVC) technique on L5 DRG neurons of normal rats and those seven days after spinal nerve axotomy (SNA). Compared to normal rats, SNA unexpectedly inhibited the activity of I_h channels on A-fiber DRG neurons: (a) the I_h current magnitude, density, and conductance were consistently diminished; and (b) the I_h activation velocity was slowed and the voltage for I_h activation was hyperpolarized. The half-activation voltage (V_0.5) exhibited a negative shift, and the time constant for I_h activation was prolonged across all test potentials, indicating the reduced availability of I_h after SNA. To further investigate the mechanisms of SNA on I_h, the underlying HCN channels and the correlated mRNA were quantified and compared. The mRNA expression level of HCN1-4 was uniformly enhanced after SNA, which might have contributed to the increased cytoplasmic HCN1 intensity observed in both medium- and large-sized DRG neurons. This finding contradicted the functional reduction of I_h after SNA. Surprisingly, the HCN labeling pattern was altered after SNA: the labeling area of HCN1 and HCN2 at the membranous ring region of the axotomized large neurons became significantly thinner or absent. We concluded that the diminished ring immunoreactivity for HCN1 and HCN2 correlated with a reduced availability of I_h channels, elucidating the observed decrease in I_h in axotomized A-fiber neurons. Full article

Glucocorticoids are known to influence hippocampal function, but their rapid non-genomic effects on specific neurons in the hippocampal trisynaptic circuit remain underexplored. This study investigated the immediate effects of glucocorticoids on CA1 and CA3 pyramidal neurons, and dentate gyrus (DG) granule neurons in rats using the patch-clamp technique. We found that a 5 min extracellular application of corticosterone significantly reduced action potential firing frequency in CA1 pyramidal neurons, while no effects were observed in CA3 or DG neurons. The corticosterone-induced inhibition in CA1 was blocked by the glucocorticoid receptor antagonist CORT125281, but remained unaffected by the mineralocorticoid receptor antagonist spironolactone. Notably, membrane-impermeable bovine serum albumin-conjugated dexamethasone mimicked corticosterone’s effects on CA1 neurons, which exhibited prominent hyperpolarization-activated cyclic nucleotide-gated (HCN) channel currents. Pyramidal neurons in CA3 and granular neurons in the DG showed little HCN channel currents. Corticosterone enhanced HCN channel activity in CA1 neurons via glucocorticoid receptors, and the HCN channel inhibitor ZD7288 abolished corticosterone’s suppressive effects on action potentials. These findings suggest that glucocorticoids selectively inhibit CA1 pyramidal neuron activity through HCN channels, providing new insight into the mechanisms of glucocorticoid action in hippocampal circuits. Full article

Parkinson’s disease (PD), the second most common neurodegenerative disease in the elderly, is characterized by selective loss of dopaminergic neurons and accumulation of α-synuclein (α-syn), mitochondrial dysfunction, Ca²⁺ dyshomeostasis, and neuroinflammation. Since current treatments for PD merely address symptoms, there is an urgent need to identify the PD pathophysiological mechanisms to develop better therapies. Increasing evidence has identified K_V3.4, a ROS-sensitive K_V channel carrying fast-inactivating currents, as a potential therapeutic target against neurodegeneration. In fact, it has been hypothesized that K_V3.4 channels could play a role in PD etiopathogenesis, controlling astrocytic activation and detrimental pathways in A53T mice, a well-known model of familial PD. Here, we showed that the A53T midbrain, primarily involved in the initial phase of PD pathogenesis, displayed an early upregulation of the K_V3.4 channel at 4 months, followed by its reduction at 12 months, compared with age-matched WT. On the other hand, in the A53T striatum, the expression of K_V3.4 remained high at 12 months, decreasing thereafter, in 16-month-old mice. The proteomic profile highlighted a different detrimental phenotype in A53T brain areas. In fact, the A53T striatum and midbrain differently expressed neuroprotective/detrimental pathways, with the variation of astrocytic p27^kip1, XIAP, and Smac/DIABLO expression. Of note, a switch from protective to detrimental phenotype was characterized by the upregulation of Smac/DIABLO and downregulation of p27^kip1 and XIAP. This occurred earlier in the A53T midbrain, at 12 months, compared with the striatum proteomic profile. In accordance, an upregulation of Smac/DIABLO and a downregulation of p27^kip1 occurred in the A53T striatum only at 16 months, showing the slowest involvement of this brain area. Of interest, HIF-1α overexpression was associated with the detrimental profile in midbrain and its major vulnerability. At the cellular level, patch-clamp recordings revealed that primary A53T striatum astrocytes showed hyperpolarized resting membrane potentials and lower firing frequency associated with K_V3.4 ROS-dependent hyperactivity, whereas primary A53T midbrain astrocytes displayed a depolarized resting membrane potential accompanied by a slight increase of K_V3.4 currents. Accordingly, intracellular Ca²⁺ homeostasis was significantly altered in A53T midbrain astrocytes, in which the ER Ca²⁺ level was lower than in A53T striatum astrocytes and the respective littermate controls. Collectively, these results suggest that the early K_V3.4 overexpression and ROS-dependent hyperactivation in astrocytes could take part in the different vulnerabilities of midbrain and striatum, highlighting astrocytic K_V3.4 as a possible new therapeutic target in PD. Full article

Transcranial electrical brain stimulation techniques like transcranial direct current (tDCS) and transcranial alternating current (tACS) have emerged as potential tools for treating neurological diseases by modulating cortical excitability. These techniques deliver small electric currents to the brain non-invasively through electrodes on the scalp. tDCS uses constant direct current which weakly alters the membrane voltage of cortical neurons, while tACS utilizes alternating current to target and enhance cortical oscillations, though the underlying mechanisms are not fully understood more specifically. To elucidate how tACS perturbs endogenous network dynamics, we simulated spiking neuron network models. We identified distinct roles of the depolarizing and hyperpolarizing phases in driving network activity towards and away from the strong nonlinearity provided by pyramidal neurons. Exploring resonance effects, we found matching tACS frequency to the network’s endogenous resonance frequency creates greater entrainment. Based on this, we developed an algorithm to determine the network’s endogenous frequency, phase, and amplitude, then deliver optimized tACS to entrain network oscillations. Together, these computational results provide mechanistic insight into the effects of tACS on network dynamics and could inform future closed-loop tACS systems that dynamically tune stimulation parameters to ongoing brain activity. Full article

Genetic testing is crucial in inherited arrhythmogenic channelopathies; however, the clinical interpretation of genetic variants remains challenging. Incomplete penetrance, oligogenic, polygenic or multifactorial forms of channelopathies further complicate variant interpretation. We identified the KCNQ1/p.D446E variant in 2/63 patients with long QT syndrome, 30-fold more frequent than in public databases. We thus characterized the biophysical phenotypes of wildtype and mutant IKs co-expressing these alleles with the β-subunit minK in HEK293 cells. KCNQ1 p.446E homozygosity significantly shifted IKs voltage dependence to hyperpolarizing potentials in basal conditions (gain of function) but failed to shift voltage dependence to hyperpolarizing potentials (loss of function) in the presence of 8Br-cAMP, a protein kinase A activator. Basal IKs activation kinetics did not differ among genotypes, but in response to 8Br-cAMP, IKs 446 E/E (homozygous) activation kinetics were slower at the most positive potentials. Protein modeling predicted a slower transition of the 446E Kv7.1 tetrameric channel to the stabilized open state. In conclusion, biophysical and modelling evidence shows that the KCNQ1 p.D446E variant has complex functional consequences including both gain and loss of function, suggesting a contribution to the pathogenesis of arrhythmogenic phenotypes as a functional risk allele. Full article

Although repolarization has been suggested to propagate in cardiac tissue both theoretically and experimentally, it has been challenging to estimate how and to what extent the propagation of repolarization contributes to relaxation because repolarization only occurs in the course of membrane excitation in normal hearts. We established a mathematical model of a 1D strand of 600 myocytes stabilized at an equilibrium potential near the plateau potential level by introducing a sustained component of the late sodium current (I_NaL). By applying a hyperpolarizing stimulus to a small part of the strand, we succeeded in inducing repolarization which propagated along the strand at a velocity of 1~2 cm/s. The ionic mechanisms responsible for repolarization at the myocyte level, i.e., the deactivation of both the I_NaL and the L-type calcium current (I_CaL), and the activation of the rapid component of delayed rectifier potassium current (I_Kr) and the inward rectifier potassium channel (I_K1), were found to be important for the propagation of repolarization in the myocyte strand. Using an analogy with progressive activation of the sodium current (I_Na) in the propagation of excitation, regenerative activation of the predominant magnitude of I_K1 makes the myocytes at the wave front start repolarization in succession through the electrical coupling via gap junction channels. Full article