Voltage-gated Potassium Channel Currents Research Articles

Low-frequency rTMS modulated the excitability and high-frequency firing in hippocampal neurons of the Alzheimer’s disease mouse model

Repetitive transcranial magnetic stimulation (rTMS), a non-invasive brain stimulation technique, holds potential for applications in the treatment of Alzheimer’s disease (AD). This study aims to compare the therapeutic effects of rTMS at different frequencies on Alzheimer’s disease and explore the alterations in neuronal electrophysiological properties throughout this process. APP/PS1 AD mice were subjected to two rTMS treatments at 0.5 Hz and 20 Hz, followed by assessments of therapeutic outcomes through the Novel Object Recognition (NOR) and Morris Water Maze (MWM) tests. Following this, whole-cell patch-clamp techniques were used to record action potential, voltage-gated sodium channel currents, and voltage-gated potassium channel currents in dentate gyrus granule neurons. The results show that AD mice exhibit significant cognitive decline compared to normal mice, along with a pronounced reduction in neuronal excitability and ion channel activity. Both frequencies of rTMS treatment partially reversed these changes, demonstrating similar therapeutic efficacy. Furthermore, the investigation indicates that low-frequency magnetic stimulation inhibited the concentrated firing of early action potentials in AD.

Effect of Titanium Particles on the Voltage-Gated Potassium Channel Currents in Trigeminal Root Ganglion Neurons.

Titanium (Ti) is the key material used in dental implants because of its excellent biocompatibility. But wear and corrosion Ti particles had been widely reported to induce inflammation and promote bone absorption. However, little information is known about the damage of Ti particles on neurons. Trigeminal root ganglion (TRG) neurons were exposed to Ti particles (<5 μm). The electrophysiological properties of 2 main subtypes of voltage-gated potassium channels (VGPCs) (KA and KV) were examined by whole-cell patch-clamp techniques. With the presence of 0.25 mg/mL Ti particles, amplitudes of IK, A and IK, V were both obviously inhibited. For IK, A, the activation V1/2 shifted to the depolarizing direction with an increased k value, whereas the inactivation V1/2 showed obvious hyperdepolarizing shifts. For IK, V, 0.5 mg/mL Ti particles produced a depolarizing shift of activation V1/2 with a slower activation rate. No significant changes of its inactivation kinetics were found. Titanium (Ti) particles might alter the electrophysiological properties of VGPCs on TRG neurons, which are likely to further influence the excitability of neurons.

Dopamine Triggers CTCF-Dependent Morphological and Genomic Remodeling of Astrocytes.

Dopamine is critical for processing of reward and etiology of drug addiction. Astrocytes throughout the brain express dopamine receptors, but consequences of astrocytic dopamine receptor signaling are not well established. We found that extracellular dopamine triggered rapid concentration-dependent stellation of astrocytic processes that was not a result of dopamine oxidation but instead relied on both cAMP-dependent and cAMP-independent dopamine receptor signaling. This was accompanied by reduced duration and increased frequency of astrocytic Ca2+ transients, but little effect on astrocytic voltage-gated potassium channel currents. To isolate possible mechanisms underlying these structural and functional changes, we used whole-genome RNA sequencing and found prominent dopamine-induced enrichment of genes containing the CCCTC-binding factor (CTCF) motif, suggesting involvement of chromatin restructuring in the nucleus. CTCF binding to promoter sites bidirectionally regulates gene transcription and depends on activation of poly-ADP-ribose polymerase 1 (PARP1). Accordingly, antagonism of PARP1 occluded dopamine-induced changes, whereas a PARP1 agonist facilitated dopamine-induced changes on its own. These results indicate that astrocyte response to elevated dopamine involves PARP1-mediated CTCF genomic restructuring and concerted expression of gene networks. Our findings propose epigenetic regulation of chromatin landscape as a critical factor in the rapid astrocyte response to dopamine.SIGNIFICANCE STATEMENT Although dopamine is widely recognized for its role in modulating neuronal responses both in healthy and disease states, little is known about dopamine effects at non-neuronal cells in the brain. To address this gap, we performed whole-genome sequencing of astrocytes exposed to elevated extracellular dopamine and combined it with evaluation of effects on astrocyte morphology and function. We demonstrate a temporally dynamic pattern of genomic plasticity that triggers pronounced changes in astrocyte morphology and function. We further show that this plasticity depends on activation of genes sensitive to DNA-binding protein CTCF. Our results propose that a broad pattern of astrocyte responses to dopamine specifically relies on CTCF-dependent gene networks.

Chlorogenic acid alters the voltage-gated potassium channel currents of trigeminal ganglion neurons.

Chlorogenic acid (5-caffeoylquinic acid, CGA) is a phenolic compound that is found ubiquitously in plants, fruits and vegetables and is formed via the esterification of caffeic acid and quinic acid. In addition to its notable biological functions against cardiovascular diseases, type-2 diabetes and inflammatory conditions, CGA was recently hypothesized to be an alternative for the treatment of neurological diseases such as Alzheimer's disease and neuropathic pain disorders. However, its mechanism of action is unclear. Voltage-gated potassium channel (Kv) is a crucial factor in the electro-physiological processes of sensory neurons. Kv has also been identified as a potential therapeutic target for inflammation and neuropathic pain disorders. In this study, we analysed the effects of CGA on the two main subtypes of Kv in trigeminal ganglion neurons, namely, the IK,A and IK,V channels. Trigeminal ganglion (TRG) neurons were acutely disassociated from the rat TRG, and two different doses of CGA (0.2 and 1 mmol⋅L−1) were applied to the cells. Whole-cell patch-clamp recordings were performed to observe alterations in the activation and inactivation properties of the IK,A and IK,V channels. The results demonstrated that 0.2 mmol⋅L−1 CGA decreased the peak current density of IK,A. Both 0.2 mmol⋅L−1 and 1 mmol⋅L−1 CGA also caused a significant reduction in the activation and inactivation thresholds of IK,A and IK,V. CGA exhibited a strong effect on the activation and inactivation velocities of IK,A and IK,V. These findings provide novel evidence explaining the biological effects of CGA, especially regarding its neurological effects.

Contributory role of endothelium and voltage-gated potassium channels in apocynin-induced vasorelaxations

Although apocynin, the nicotinamide adenine dinucleotide phosphate oxidase inhibitor improves vascular function in hypertension, its specificity has been questioned. The present study examined whether apocynin-induced vasorelaxations involve endothelium and/or K channels in vascular cells. Aortas from Sprague-Dawley rats were suspended in organ baths for functional studies. Changes in intracellular calcium ([Ca]i) and nitric oxide ([NO]i) in rat endothelial cells were detected by fluorescence imaging. Whole-cell voltage-gated K (Kv) currents were recorded in vascular smooth muscle cells. Apocynin-induced aortic relaxations were attenuated by the absence of endothelium, endothelial nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester, or nitric oxide-dependent soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one. 4-Aminopyridine (4-AP, voltage-gated potassium channels blocker) attenuated apocynin-induced relaxations, its combined treatment with 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) did not cause further inhibition. Apocynin increased [Ca]i and [NO]i in endothelial cells, which were abolished by 4-AP, indicating the involvement of voltage-gated potassium channels in endothelial cells. In addition, apocynin-stimulated increase in endothelial nitric oxide synthase phosphorylation at Ser depended on the presence of extracellular Ca. Notably, 4-AP also reduced apocynin-induced relaxations in the absence of endothelium and apocynin increased 4-AP-sensitive voltage-gated potassium channel currents in vascular smooth muscle cells. This study provides novel data showing that apocynin-induced relaxations of rat aortas are mediated by 4-AP-sensitive stimulation of [Ca]i and [NO]i increases in endothelium and by activation of voltage-gated potassium channels in vascular smooth muscle cells.

TNF-α differentially modulates ion channels of nociceptive neurons

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine involved in the development and maintenance of inflammatory and neuropathic pain conditions. The mechanisms by which TNF-alpha elicits pain behavior are still incompletely understood. Numerous studies suggest that TNF-alpha sensitizes primary afferent neurons. Most recently, it was shown that TNF-alpha induced an enhancement of TTX-R Na(+) current in dorsal root ganglion (DRG) cells. In the present study, we have tested the effect of acute application of TNF-alpha on voltage-gated potassium, calcium and sodium channel currents as well as its influence on membrane conductance in isolated rat DRG neurons. We report that voltage-gated potassium channel currents of nociceptive DRG neurons are not influenced by TNF-alpha (100 ng/ml), while voltage-gated calcium channel currents were decreased voltage-dependently by -7.73+/-6.01% (S.D.), and voltage-activated sodium channels currents were increased by +5.62+/-4.27%, by TNF-alpha. In addition, TNF-alpha induced a significant increase in IV ramps at a potential of +20 mV, which did not exist when the experiments were conducted in a potassium-free solution, indicating that this effect is mainly the result of a change in potassium conductance. These different actions of TNF-alpha might help to explain how it sensitizes primary afferent neurons after nerve injury and thus facilitates pain.

Effects of static magnetic fields on the voltage-gated potassium channel currents in trigeminal root ganglion neurons

To evaluated the effects of moderate-intensity static magnetic fields (SMF) on two types of voltage-gated potassium channel (VGPC) currents: I K,A and I K,V, whole-cell patch-clamp experiments were conducted on acute dissociated rat trigeminal root ganglion (TRG) neurons. The results demonstrated that 125 mT SMF could influence the inactivation kinetics of these two VGPC currents by altering the inactivation rate and velocity. No significant change was observed in the activation properties. These findings supported the hypothesis that biological membrane would be deformed in moderate-intensity SMF and the physiological characteristics of ion channels on the membrane would be influenced. The mechanism underlying the different effects of SMF on the I K,A and I K,V inactivation was also discussed.

Purinergic Receptor Identification and Regulation of Voltage‐gated K + Channels in AML 14.3D10 Cells, a Human Eosinophil‐like Cell Line

The AML14 cell line and its AML14.3D10 subclone was established as a model cell system that exhibits phenotypic characteristics similar to that of human eosinophils. We investigated the effects of purinergic receptor stimulation on the physiological response of the AML 14.3D10 cell line to better evaluate its role as a suitable model for eosinophils using both molecular and functional approaches. Ca2+ imaging experiments using Fura-2 demonstrated the existence of purinergic receptors responsive to UTP (EC50 of 8.9 x 10−8), ATP γ-s (EC50 of 1.87 x 10−7), and UDP (EC50 of 7.44x 10−6). Molecular identification of the purinergic receptor subtypes was confirmed by QRT-PCR which demonstrated the presence of P2Y1, P2Y2, P2Y4, and P2Y6 receptors. Ratio imaging experiments using the membrane potential sensitive indicator DiBAC-3 showed that stimulation with UTP produced a membrane hyperpolarization of approximately 10 mV that returned to the original resting potential within 10 minutes after stimulation. Whole cell perforated patch clamp experiments using amphotericin B revealed the presence of voltage-gated potassium channel currents that were stimulated following treatment with UTP. Analysis of mRNA by QRT-PCR indicated the existence of several voltage-gated potassium channel α subunits including, Kv1.2, Kv1.3, Kv1.4, and Kv1.6. Previous studies of Kv1.3 channel function in T-lymphocytes showed that the channel was involved in activation and proliferation, suggesting the possibility of a similar role related to tumorogenesis in the AML 14.3D10 cell line.

Neuromyotonia

There is increasing evidence that autoimmunity is implicated in the pathogenesis of peripheral nerve hyperexcitability (neuromyotonia, NMT and Cramp-fasciculation syndrome C-FS ) and in Maladie de Morvan in which CNS features are also present. All three conditions can associate with thymoma, myasthenia gravis and other autoimmune disorders, and can often respond to plasma exchange. In NMT, patient's plasma or IgG can transfer the electrophysiological features to mice, and can reduce voltage-gated potassium channel currents in vitro. Antibodies to voltage-gated potassium channels can be detected in the serum of many patients who have peripheral nerve hyperexcitability, and also in those with Maladie de Morvan. These latter patients have clinical features similar to limbic encephalitis in which VGKC antibodies can also occur. Thus neuromyotonia, cramp-fasciculation syndrome and Maladie de Morvan can occur as antibody-mediated autoimmune ion channelopathies like myasthenia gravis and the Lambert-Eaton myasthenic syndrome. These discoveries should aid diagnosis and offer new approaches to treatment.

Reversal of chronic hypoxia-induced alterations in pulmonary artery smooth muscle electromechanical coupling upon air breathing.

Chronic hypoxia (CH) induces selective pulmonary hypertension which is accompanied by structural and functional alterations in the pulmonary vasculature. Little information is available on the regression of CH-induced functional alterations of pulmonary wall. In the present work, we investigated the reversal of CH-induced pulmonary hypertension with a special focus on alterations in the electrophysiological properties of pulmonary artery smooth muscle cells (PAMCs) after normoxia recovery. Rats were exposed to a hypobaric environment for 3 weeks (CH rats) and then subjected to a normoxic environment for 3 weeks (normoxia-recovery group) and compared with rats maintained in a normoxic environment (control rats). Electrophysiological properties of PAMCs were studied using conventional microelectrodes and patch-clamp technique. CH rats exhibited a threefold increase in pulmonary blood pressure compared to control rats and this increase was fully reversed following 3 weeks of normoxia. PAMCs from CH rats were depolarised (about 20 mV), had an elevated calcium concentration and exhibited a hypersensitivity to 4-aminopyridine (4-AP) of membrane potential as well as the tone of arterial rings compared with tissues from control rats. Whole cell patch-clamp recordings indicated that voltage gated potassium channel currents I(Kv) and I(K(N)) were decreased in PAMCs from CH rats with a hyper sensitivity of I(K(N)) to 4-AP. CH-induced alterations in electrophysiological properties of PAMCs were also fully reversed after 3 weeks of normoxia recovery. Both the increase in the pulmonary blood pressure and alterations in electrophysiological properties of PASMCs simultaneously reverse after normoxia recovery. This complete reversibility of all of the CH-induced pulmonary vascular alterations suggests that curative treatments for PAHT may now be designed aimed at targeting the very limited key factors implicated in hypoxia sensing.