Kv Currents Research Articles

Increased Expression of MicroRNA-206 Inhibits Potassium Voltage-Gated Channel Subfamily A Member 5 in Pulmonary Arterial Smooth Muscle Cells and Is Related to Exaggerated Pulmonary Artery Hypertension Following Intrauterine Growth Retardation in Rats.

BackgroundIntrauterine growth retardation (IUGR) is related to pulmonary artery hypertension in adults, and microRNA‐206 (miR‐206) is proposed to affect the proliferation and apoptosis of pulmonary artery smooth muscle cells (PASMCs) via post‐transcriptional regulation.Methods and ResultsIn an IUGR rat model, we found that the expression and function of potassium voltage‐gated channel subfamily A member 5 (Kv1.5) in PASMCs was inhibited, and pulmonary artery hypertension was exaggerated after chronic hypoxia (CH) treatment as adults. microRNA expression was investigated in PASMCs from 12‐week‐old male IUGR rats with CH by microarray, polymerase chain reaction, and in situ hybridization. The expression levels of Kv1.5 in primary cultured PASMCs and pulmonary artery smooth muscle from IUGR or control rats were evaluated with and without application of an miR‐206 inhibitor. Right ventricular systolic pressure, cell proliferation, luciferase reporter assay, and IK v were also calculated. We found increased expression of miR‐206 in resistance pulmonary arteries of IUGR rats at 12 weeks compared with newborns. Application of an miR‐206 inhibitor in vivo or in vitro increased expression of Kv1.5 α‐protein and KCNA5. Also, decreased right ventricular systolic pressure and cell proliferation were observed in PASMCs from 12‐week‐old control and IUGR rats after CH, while inhibitor did not significantly affect control and IUGR rats.ConclusionsThese results suggest that expression of Kv1.5 and 4‐aminopyridine (Kv channel special inhibitor)‐sensitive Kv current were correlated with the inhibition of miR‐206 in PA rings of IUGR‐CH rats and cultured IUGR PASMCs exposed to hypoxia. Thus, miR‐206 may be a trigger for induction of exaggerated CH–pulmonary artery hypertension of IUGR via Kv1.5.

The sources of electrophysiological variability in the retina of Periplaneta americana.

Variability in the electrophysiological properties of homotypic photoreceptors is widespread and is thought to facilitate functioning under disparate illumination conditions. Compound eyes of insects have three sources of variability: inter-individual, intra-individual, and intra-ommatidial, the latter two overlapping. Here, I explored the causes of variability in Periplaneta americana, a nocturnal insect characterized by highly variable photoreceptor responses. By recording from photoreceptors in dissociated ommatidia, including consecutive recordings from photoreceptors in the same ommatidium (SO), I studied the variability of six properties: whole-cell membrane capacitance (Cm), phototransduction latency, maximal conductance (Gmax) and the slope factor of the sustained Kv current, absolute sensitivity in dim light, and sustained light-induced current (LIC) amplitude in bright light. Coefficient of variation (CV) metrics were used to compare variances in four experimental groups: SO, same animal (SA), all data combined "full sample" (FS), and full sample of all SO recordings (FSSO). For the normally distributed parameters Cm, Gmax, slope factor, and latency, the highest CV values were found in FS and FSSO, intermediate in SA, and the lowest in SO. On average, SO variance accounted for 47% of the full-sample variance in these four parameters. Absolute sensitivity and LIC values were not normally distributed, and the differences in variability between SO and FS/FSSO groups were smaller than for the other four parameters. These results indicate two main sources of variability, intra-ommatidial and inter-individual. Inter-individual variability was investigated by exposing adult cockroaches to constant light or dark for several months. In both groups, the majority of CV measures for the six parameters decreased compared to control, indicating substantial contribution of phenotypic plasticity to inter-individual differences. Analysis of variability of resting potential and elementary voltage responses revealed that resting potential is mainly determined by the sustained Kv conductance, whereas voltage bump amplitude is mainly determined by current bump amplitude and Cm.

CARE Dose 4D combined with sinogram-affirmed iterative reconstruction improved the image quality and reduced the radiation dose in low dose CT of the small intestine.

ObjectiveMultislice computed tomography (MSCT) has been used for diagnosis of small intestinal diseases. However, the radiation dose is a big problem. This study was to investigate whether CARE Dose 4D combined with sinogram‐affirmed iterative reconstruction (SAFIRE) can provide better image quality at a lower dose for imaging small intestinal diseases compared to MSCT.MethodsThe noise reduction ability of SAFIRE was assessed by scanning the plain water mold using SOMATOM Definition Flash double‐source spiral CT. CT images at each stage of radiography for 239 patients were obtained. The patients were divided into groups A and B were based on different tube voltage and current or the image recombination methods. The images were restructured using with filtered back projection (FBP) and SAFIRE (S1–S5). The contrast noise ratio (CNR), CT Dose index (CTDI), subjective scoring, and objective scoring were compared to obtain the best image and reformation parameters at different stages of CT.ResultsTwenty‐six restructuring patterns of tube voltage and current were obtained by FBP and SAFIRE. The average radiation dose using CARE Dose 4D combined with SAFIRE (S4–S5) reduced approximately 74.85% compared to conditions where the tube voltage of 100 kV and tube current of 131 mAs for patients with MSCT small intestinal CT enterography at plain CT scan, arterial stage, small intestine, and portal venous phase. The objective and subjective scoring were all significantly different among groups A and B at each stage.ConclusionsCombination of CARE Dose 4D and SAFIRE is shown to decrease the radiation dose while maintaining image quality.

Sex- and Development-Dependent Responses of Rat Microglia to Pro- and Anti-inflammatory Stimulation.

Addressing potential sex differences in pre-clinical studies is crucial for developing therapeutic interventions. Although sex differences have been reported in epidemiological studies and from clinical experience, most pre-clinical studies of neuroinflammation use male rodents; however, sexual dimorphisms in microglia might affect the CNS inflammatory response. Developmental changes are also important and, in rodents, there is a critical period of sexual brain differentiation in the first 3 weeks after birth. We compared rat microglia from sex-segregated neonates (P1) and at about the time of weaning (P21). To study transitions from a basal homeostatic state (untreated), microglia were subjected to a pro-inflammatory (IFNγ + TNFα) or anti-inflammatory (IL-4) stimulus. Responses were compared by quantifying changes in nitric oxide production, migration, and expression of nearly 70 genes, including inflammatory mediators and receptors, inflammasome molecules, immune modulators, and genes that regulate microglial physiological functions. No sex differences were seen in transcriptional responses in either age group but the IL-4-evoked migration increase was larger in male cells at both ages. Protein changes for the hallmark molecules, NOS2, COX-2, PYK2 and CD206 correlated with mRNA changes. P1 and P21 microglia showed substantial differences, including expression of genes related to developmental roles. That is, P21 microglia had a more mature phenotype, with higher basal and stimulated levels of many inflammatory genes, while P1 cells had higher expression of phagocytosis-related molecules. Nevertheless, cells of both ages responded to IL-4 and IFNγ + TNFα. We examined the Kv1.3 potassium channel (a potential target for modulating neuroinflammation) and the Kir2.1 channel, which regulate several microglia functions. Kv1.3 mRNA (Kcna3) was higher at P21 under all conditions and male P21 cells had higher mRNA and Kv currents in response to IFNγ + TNFα. Overall, numerous transcriptional and functional responses of microglia changed during the first 3 weeks after birth but few sex-dependent changes were seen.

Molecular basis involved in the blocking effect of antidepressant metergoline on C-type inactivation of Kv1.4 channel

Voltage-gated potassium channels (VGKCs) are transmembrane ion channels specific for potassium. Currently there are nine kinds of VGKCs. Kv1.4 is one of shaker-related potassium channels. It is a representative alpha subunit of potassium channels that can inactivate A type-currents, leading to N pattern inactivation. Inactivation of Kv channels plays an important role in shaping electrical signaling properties of neuronal and muscular cells. The shape of N pattern inactivation can be modified by removing the N-terminal (NT) domain which results in non-inactivated currents and C pattern inactivation. In a previous work, we have reported the regulatory effect of metergoline on Kv1.4 and Nav1.2 channel activity. In the present study, we constructed a mutant of deleted 61 residues from NT of Kv1.4 channels (Kv1.4 Δ2-61) and found that it induced an outward peak and steady-state currents We also studied the modulation effect of metergoline on the activity of this Kv1.4 Δ2-61 mutant channel without having the N-terminal quick inactivation domain. Our results revealed that treatment with metergoline inhibited NT deleted Kv1.4 mutant channel activity in a concentration-dependent manner which was reversible. Interestingly, metergoline treatment induced little effects on the outward peak current in the deleted Kv1.4 mutant channel. However, metergoline treatment conspicuously inhibited steady state currents of Kv1.4 Δ2-61 channels with acceleration current mode. The acceleration of steady-state current of deleted Kv1.4 mutant channel occurred in a concentration-dependent manner. This means that metergoline can accelerate C pattern inactivation of Kv1.4 Δ2-61 channel by acting as an open state dependent channel blocker. We also performed site-directed mutations in V561A and K532Y, also known as C-type inactivation sites. V561A, K532Y, and V561A + K532Y substitution mutants significantly attenuated the acceleration effect of metergoline on C pattern inactivation of hKv1.4 channel currents. In docking modeling study, predicted binding residues for metergoline were analyzed for six amino acids. Among them, the K532 residue known as the C-type inactivation site was analyzed to be a major site of action. Then various mutants were constructed. K532 substitution mutant significantly abolished the effect of metergoline on Kv1.4 currents among various mutants whereas other changes had slight inhibitory effects. Furthermore, we found that metergoline had specificity for Kv1.4, but not for Kv1.5 currents. In addition, the A type current in rat neuronal cell was inhibited and accelerated of inactivation. This result further shows that metergoline might interact with Lys532 residue and then accelerate C pattern inactivation of Kv1.4 channels with channel type specificity. Taken together, these results demonstrate the molecular basis involved in the effect of metergoline, an ergot alkaloid, on human Kv1.4 channel, providing a novel interaction ligand.

Improvement of the Beam-Wave Interaction Efficiency Based on the Coupling-Slot Configuration in an Extended Interaction Oscillator

A method aimed at improving the beam-wave interaction efficiency by changing the coupling slot configuration has been proposed in the study of extended interaction oscillators (EIOs). The dispersion characteristics, coupling coefficient and interaction impedance of the high-frequency structure based on different types of coupling slots have been investigated. Four types of coupled cavity structures with different layouts of the coupling slots have been compared to improve the beamwave interaction efficiency, so as to analyze the beam-wave interaction and practical applications. In order to determine the improvement of the coupling slot to a coupled cavity circuit in an EIO, we designed four nine-gap EIOs based on the coupled cavity structure with different coupling slot configurations. With different operating frequencies and voltages takes into consideration, beam voltages from 27 to 33 kV have been simulated to achieve the best beam-wave interaction efficiency so that the EIOs are able to work in the 2π mode. The influence of the Rb and the ds on the output power is also taken into consideration. The Rb is the radius of the electron beam, and the ds is the width of the coupling slot. The simulation results indicate that a single-slot-type EIO has the best beam-wave interaction efficiency. Its maximum output power is 2.8 kW and the efficiency is 18% when the operating voltage is 31 kV and electric current is 0.5 A. The output powers of these four EIOs that were designed for comparison are not less than 1.7 kW. The improved coupling-slot configurations enables the extended interaction oscillator to meet the different engineering requirements better.

Sodium and potassium conductances in principal neurons of the mouse piriform cortex: a quantitative description.

The primary olfactory (or piriform) cortex is a promising model system for understanding how the cerebral cortex processes sensory information, although an investigation of the piriform cortex is hindered by a lack of detailed information about the intrinsic electrical properties of its component neurons. In the present study, we quantify the properties of voltage-dependent sodium currents and voltage- and calcium-dependent potassium currents in two important classes of excitatory neurons in the main input layer of the piriform cortex. We identify several classes of these currents and show that their properties are similar to those found in better-studied cortical regions. Our detailed quantitative descriptions of these currents will be valuable to computational neuroscientists who aim to build models that explain how the piriform cortex encodes odours. The primary olfactory cortex (or piriform cortex, PC) is an anatomically simple palaeocortex that is increasingly used as a model system for investigating cortical sensory processing. However, little information is available on the intrinsic electrical conductances in neurons of the PC, hampering efforts to build realistic computational models of this cortex. In the present study, we used nucleated macropatches and whole-cell recordings to rigorously quantify the biophysical properties of voltage-gated sodium (NaV ), voltage-gated potassium (KV ) and calcium-activated potassium (KCa ) conductances in two major classes of glutamatergic neurons in layer 2 of the PC, semilunar (SL) cells and superficial pyramidal (SP) cells. We found that SL and SP cells both express a fast-inactivating NaV current, two types of KV current (A-type and delayed rectifier-type) and three types of KCa current (fast-, medium- and slow-afterhyperpolarization currents). The kinetic and voltage-dependent properties of the NaV and KV conductances were, with some exceptions, identical in SL and SP cells and similar to those found in neocortical pyramidal neurons. The KCa conductances were also similar across the different types of neurons. Our results are summarized in a series of empirical equations that should prove useful to computational neuroscientists seeking to model the PC. More broadly, our findings indicate that, at the level of single-cell electrical properties, this palaeocortex is not so different from the neocortex, vindicating efforts to use the PC as a model of cortical sensory processing in general.

Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular KV currents and predisposes to ventricular arrhythmia.

KCNE5 is an X-linked gene encoding KCNE5, an ancillary subunit to voltage-gated potassium (KV) channels. Human KCNE5 mutations are associated with atrial fibrillation (AF)- and Brugada syndrome (BrS)-induced cardiac arrhythmias that can arise from increased potassium current in cardiomyocytes. Seeking to establish underlying molecular mechanisms, we created and studied Kcne5 knockout ( Kcne5-/0) mice. Intracardiac ECG revealed that Kcne5 deletion caused ventricular premature beats, increased susceptibility to induction of polymorphic ventricular tachycardia (60 vs. 24% in Kcne5+/0 mice), and 10% shorter ventricular refractory period. Kcne5 deletion increased mean ventricular myocyte KV current density in the apex and also in the subpopulation of septal myocytes that lack fast transient outward current ( Ito,f). The current increases arose from an apex-specific increase in slow transient outward current-1 ( IKslow,1) (conducted by KV1.5) and Ito,f (conducted by KV4) and an increase in IKslow,2 (conducted by KV2.1) in both apex and septum. Kcne5 protein localized to the intercalated discs in ventricular myocytes, where KV2.1 was also detected in both Kcne5-/0 and Kcne5+/0 mice. In HL-1 cardiac cells and human embryonic kidney cells, KCNE5 and KV2.1 colocalized at the cell surface, but predominantly in intracellular vesicles, suggesting that Kcne5 deletion increases IK,slow2 by reducing KV2.1 intracellular sequestration. The human AF-associated mutation KCNE5-L65F negative shifted the voltage dependence of KV2.1-KCNE5 channels, increasing their maximum current density >2-fold, whereas BrS-associated KCNE5 mutations produced more subtle negative shifts in KV2.1 voltage dependence. The findings represent the first reported native role for Kcne5 and the first demonstrated Kcne regulation of KV2.1 in mouse heart. Increased KV current is a manifestation of KCNE5 disruption that is most likely common to both mouse and human hearts, providing a plausible mechanistic basis for human KCNE5-linked AF and BrS.-David, J.-P., Lisewski, U., Crump, S. M., Jepps, T. A., Bocksteins, E., Wilck, N., Lossie, J., Roepke, T. K., Schmitt, N., Abbott, G. W. Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular KV currents and predisposes to ventricular arrhythmia.

AbeTx1 Is a Novel Sea Anemone Toxin with a Dual Mechanism of Action on Shaker-Type K⁺ Channels Activation.

Voltage-gated potassium (KV) channels regulate diverse physiological processes and are an important target for developing novel therapeutic approaches. Sea anemone (Cnidaria, Anthozoa) venoms comprise a highly complex mixture of peptide toxins with diverse and selective pharmacology on KV channels. From the nematocysts of the sea anemone Actinia bermudensis, a peptide that we named AbeTx1 was purified and functionally characterized on 12 different subtypes of KV channels (KV1.1–KV1.6; KV2.1; KV3.1; KV4.2; KV4.3; KV11.1; and, Shaker IR), and three voltage-gated sodium channel isoforms (NaV1.2, NaV1.4, and BgNaV). AbeTx1 was selective for Shaker-related K+ channels and is capable of inhibiting K+ currents, not only by blocking the K+ current of KV1.2 subtype, but by altering the energetics of activation of KV1.1 and KV1.6. Moreover, experiments using six synthetic alanine point-mutated analogs further showed that a ring of basic amino acids acts as a multipoint interaction for the binding of the toxin to the channel. The AbeTx1 primary sequence is composed of 17 amino acids with a high proportion of lysines and arginines, including two disulfide bridges (Cys1–Cys4 and Cys2–Cys3), and it is devoid of aromatic or aliphatic amino acids. Secondary structure analysis reveals that AbeTx1 has a highly flexible, random-coil-like conformation, but with a tendency of structuring in the beta sheet. Its overall structure is similar to open-ended cyclic peptides found on the scorpion κ-KTx toxins family, cone snail venoms, and antimicrobial peptides.

Short-term high glucose culture potentiates pancreatic beta cell function

The exposure of pancreatic islets to high glucose is believed to be one of the causal factors of the progressive lowering of insulin secretion in the development of type 2 diabetes. The progression of beta cell failure to type 2 diabetes is preceded by an early positive increase in the insulin secretory response to glucose, which is only later followed by a loss in the secretion capacity of pancreatic islets. Here we have investigated the electrophysiological mechanisms underlying the early glucose-mediated gain of function. Rodent pancreatic islets or dispersed islet cells were cultured in medium containing either 5.6 (control) or 16.7 (high-glucose) mM glucose for 24 h after isolation. Glucose-stimulated insulin secretion was enhanced in a concentration-dependent manner in high glucose-cultured islets. This was associated with a positive effect on beta cell exocytotic capacity, a lower basal KATP conductance and a higher glucose sensitivity to fire action potentials. Despite no changes in voltage-gated Ca2+ currents were observed in voltage-clamp experiments, the [Ca2+]I responses to glucose were drastically increased in high glucose-cultured cells. Of note, voltage-dependent K+ currents were decreased and their activation was shifted to more depolarized potentials by high-glucose culture. This decrease in voltage-dependent K+ channel (Kv) current may be responsible for the elevated [Ca2+]I response to metabolism-dependent and independent stimuli, associated with more depolarized membrane potentials with lower amplitude oscillations in high glucose-cultured beta cells. Overall these results show that beta cells improve their response to acute challenges after short-term culture with high glucose by a mechanism that involves modulation not only of metabolism but also of ion fluxes and exocytosis, in which Kv activity appears as an important regulator.

HIV transgene expression impairs K+ channel function in the pulmonary vasculature.

Human immunodeficiency virus (HIV) infection is an established risk factor for pulmonary arterial hypertension (PAH); however, the pathogenesis of HIV-related PAH remains unclear. Since K+ channel dysfunction is a common marker in most forms of PAH, our aim was to analyze whether the expression of HIV proteins is associated with impairment of K+ channel function in the pulmonary vascular bed. HIV transgenic mice (Tg26) expressing seven of the nine HIV viral proteins and wild-type (WT) mice were used. Hemodynamic assessment was performed by echocardiography and catheterization. Vascular reactivity was studied in endothelium-intact pulmonary arteries. K+ currents were recorded in freshly isolated pulmonary artery smooth muscle cells (PASMC) using the patch-clamp technique. Gene expression was assessed using quantitative RT-PCR. PASMC from Tg26 mice had reduced K+ currents and were more depolarized than those from WT. Whereas voltage-gated K+ channel 1.5 (Kv1.5) currents were preserved, pH-sensitive noninactivating background currents ( IKN) were nearly abolished in PASMC from Tg26 mice. Tg26 mice had reduced lung expression of Kv7.1 and Kv7.4 channels and decreased responses to the Kv7.1 channel activator L-364,373 assessed by vascular reactivity and patch-clamp experimental approaches. Although we found pulmonary vascular remodeling and endothelial dysfunction in Tg26 mice, this was not accompanied by changes in hemodynamic parameters. In conclusion, the expression of HIV proteins in vivo impairs pH-sensitive IKN and Kv7 currents. This negative impact of HIV proteins in K+ channels was not sufficient to induce PAH, at least in mice, but may play a permissive or accessory role in the pathophysiology of HIV-associated PAH.

Characterization and molecular basis for the block of Kv1.3 channels induced by carvedilol in HEK293 cells

Carvedilol is a non-selective β-adrenoreceptor antagonist and exhibits a wide range of biological activities. The voltage-gated K+ (Kv) channel is one of the target ion channels of this compound. The rapidly activating Kv1.3 channel is expressed in several different tissues and plays an important role in the regulation of physiological functions, including cell proliferation and apoptosis. However, little is known about the possible action of carvedilol on Kv1.3 currents. Using the whole-cell configuration of the patch-clamp technique, we have revealed that exposure to carvedilol produced a concentration-dependent blocking of Kv1.3 channels heterologously expressed in HEK293 cells, with an IC50 value of 9.7 μM. This chemical decelerated the deactivation tail current of Kv1.3 currents, resulting in a tail crossover phenomenon. In addition, carvedilol generated a markedly hyperpolarizing shift (20 mV) of the inactivation curve, but failed to affect the activation curve. Mutagenesis experiments of Kv1.3 channels identified G427 and H451, two related sites of TEA block, as important residues for carvedilol-mediated blocking. The present results suggest that carvedilol acts directly on Kv1.3 currents by inducing closed- and open-channel block and helps to elucidate the mechanisms of action of this compound on Kv channels.

MAPKs-mediated modulation of the myocyte voltage-gated K+ channels is involved in ethanol-induced rat coronary arterial contraction

Acute coronary arterial spasm is contributory to ethanol-induced heart ischemic events. The present experiments were designed to study contractive effect of ethanol in isolated rat coronary arteries (RCAs) stimulated mildly with vasoconstrictors and involvement of voltage-gated potassium (KV) channels and mitogen-activated protein kinases (MAPKs) of rat coronary arterial smooth muscle cell (RCASMC) in the spasm. The vascular tension was recorded with a wire myograph. KV currents of single freshly isolated RCASMC were assessed with patch clamp. Phosphorylation of RCASMC MAPKs (p38 MAPK and p44/42 MAPK) was assayed by Western blots. Mild stimulation, which was defined as 5–20% of 60 mM KCl-induced contraction, with thromboxane A2 mimetic U46619, endothelin-1 or KCl tremendously increased contractive response of RCAs to ethanol (0.8–8.0 mg/ml). Ethanol (8 and 25 mg/ml) reduced the maximal KV currents by 53.6% and 56.6% respectively without concentration-dependence. Both ethanol (8.0 mg/ml) and U46619 (0.3 μM) enhanced phosphorylation of p38 MAPK and p44/42 MAPK and there was a pronounced synergism between them. MAPK pathway inhibition with p38 MAPK inhibitor SB239063 and p44/42 MAPK inhibitor PD98059 depressed ethanol-induced contraction by 22–55% in the stimulated RCAs and almost abrogated ethanol-induced reduction in KV currents. The present results for the first time demonstrated that ethanol induces potent vasoconstriction in stimulated RCAs and depresses KV currents in RCASMCs. It is suggested that MAPKs pathways play an important role in the etiology of ethanol-induced coronary artery diseases.

Differential effect of Androctonus australis hector venom components on macrophage KV channels: electrophysiological characterization.

Neurotoxins of scorpion venoms modulate ion channels. Voltage-gated potassium (KV) channels regulate the membrane potential and are involved in the activation and proliferation of immune cells. Macrophages are key components of the inflammatory response induced by scorpion venom. The present study was undertaken to investigate the effect of Androctonus australis hector (Aah) venom on KV channels in murine resident peritoneal macrophages. The cytotoxicity of the venom was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) -based assay and electrophysiological recordings were performed using the whole-cell patch clamp technique. High doses of Aah venom (50, 125, 250 and 500µg/ml) significantly decreased cell viability, while concentrations of 0.1-25µg/ml were not cytotoxic towards peritoneal macrophages. Electrophysiological data revealed a differential block of KV current between resting and LPS-activated macrophages. Aah venom significantly reduced KV current amplitude by 62.5 ± 4.78% (n = 8, p < 0.05), reduced the use-dependent decay of the current, decreased the degree of inactivation and decelerated the inactivation process of KV current in LPS-activated macrophages. Unlike cloned KV1.5channels, Aah venom exerted a similar blocking effect on KV1.3 compared to KV current in LPS-activated macrophages, along with a hyperpolarizing shift in the voltage dependence of KV1.3 inactivation, indicating a direct mechanism of current inhibition by targeting KV1.3 subunits. The obtained results, demonstrating that Aah venom differentially targets KV channels in macrophages, suggest differentialoutcomesfor their inhibitions, and that further investigations of scorpion venom immunomodulatory potential are required.

Coupling of Smoothened to inhibitory G proteins reduces voltage-gated K+ currents in cardiomyocytes and prolongs cardiac action potential duration

SMO (Smoothened), the central transducer of Hedgehog signaling, is coupled to heterotrimeric Gi proteins in many cell types, including cardiomyocytes. In this study, we report that activation of SMO with SHH (Sonic Hedgehog) or a small agonist, purmorphamine, rapidly causes a prolongation of the action potential duration that is sensitive to a SMO inhibitor. In contrast, neither of the SMO agonists prolonged the action potential in cardiomyocytes from transgenic GiCT/TTA mice, in which Gi signaling is impaired, suggesting that the effect of SMO is mediated by Gi proteins. Investigation of the mechanism underlying the change in action potential kinetics revealed that activation of SMO selectively reduces outward voltage-gated K+ repolarizing (Kv) currents in isolated cardiomyocytes and that it induces a down-regulation of membrane levels of Kv4.3 in cardiomyocytes and intact hearts from WT but not from GiCT/TTA mice. Moreover, perfusion of intact hearts with Shh or purmorphamine increased the ventricular repolarization time (QT interval) and induced ventricular arrhythmias. Our data constitute the first report that acute, noncanonical Hh signaling mediated by Gi proteins regulates K+ currents density in cardiomyocytes and sensitizes the heart to the development of ventricular arrhythmias.

Diverse Intrinsic Properties Shape Functional Phenotype of Low-Frequency Neurons in the Auditory Brainstem.

In the auditory system, tonotopy is the spatial arrangement of where sounds of different frequencies are processed. Defined by the organization of neurons and their inputs, tonotopy emphasizes distinctions in neuronal structure and function across topographic gradients and is a common feature shared among vertebrates. In this study we characterized action potential firing patterns and ion channel properties from neurons located in the extremely low-frequency region of the chicken nucleus magnocellularis (NM), an auditory brainstem structure. We found that NM neurons responsible for encoding the lowest sound frequencies (termed NMc neurons) have enhanced excitability and fired bursts of action potentials to sinusoidal inputs ≤10 Hz; a distinct firing pattern compared to higher-frequency neurons. This response property was due to lower amounts of voltage dependent potassium (KV) conductances, unique combination of KV subunits and specialized sodium (NaV) channel properties. Particularly, NMc neurons had significantly lower KV1 and KV3 currents, but higher KV2 current. NMc neurons also showed larger and faster transient NaV current (INaT) with different voltage dependence of inactivation from higher-frequency neurons. In contrast, significantly smaller resurgent sodium current (INaR) was present in NMc with kinetics and voltage dependence that differed from higher-frequency neurons. Immunohistochemistry showed expression of NaV1.6 channel subtypes across the tonotopic axis. However, various immunoreactive patterns were observed between regions, likely underlying some tonotopic differences in INaT and INaR. Finally, using pharmacology and computational modeling, we concluded that KV3, KV2 channels and INaR work synergistically to regulate burst firing in NMc.

MiR-1 is increased in pulmonary hypertension and downregulates Kv1.5 channels in rat pulmonary arteries.

The expression of miR-1 is increased in lungs from the Hyp/Su5416 PAH rat model. Pulmonary artery smooth muscle cells from this animal model are more depolarized and show decreased expression and activity of voltage-dependent potassium channel (Kv)1.5. miR-1 directly targets Kv1.5 channels, reduces Kv1.5 activity and induces membrane depolarization. Antagomir-1 prevents Kv1.5 channel downregulation and the depolarization induced by hypoxia/Su5416 exposition. Impairment of the voltage-dependent potassium channel (Kv) plays a central role in the development of cardiovascular diseases, including pulmonary arterial hypertension (PAH). MicroRNAs are non-coding RNAs that regulate gene expression by binding to the 3'-untranslated region region of specific mRNAs. The present study aimed to analyse the effects of miR-1 on Kv channel function in pulmonary arteries (PA). Kv channel activity was studied in PA from healthy animals transfected with miR-1 or scrambled-miR. Kv currents were studied using the whole-cell configuration of the patch clamp technique. The characterization of the Kv1.5 currents was performed with the selective inhibitor DPO-1. miR-1 expression was increased and Kv1.5 channels were decreased in lungs from a rat model of PAH induced by hypoxia and Su5416. miR-1 transfection increased cell capacitance, reduced Kv1.5 currents and induced membrane depolarization in isolated pulmonary artery smooth muscle cells. A luciferase reporter assay indicated that KCNA5, which encodes Kv1.5 channels, is a direct target gene of miR-1. Incubation of PA with Su5416 and hypoxia (3% O2 ) increased miR-1 and induced a decline in Kv1.5 currents, which was prevented by antagomiR-1. In conclusion, these data indicate that miR-1 induces pulmonary artery smooth muscle cell hypertrophy and reduces the activity and expression of Kv channels, suggesting a pathophysiological role in PAH.

Novel Insights Into the Mechanisms of Abdominal Pain in Obstructive Bowel Disorders.

Obstructive bowel disorders (OBD) are characterized by lumen distention due to mechanical or functional obstruction in the gut. Abdominal pain is one of the main symptoms in OBD. In this article, we aim to critically review the potential mechanisms for acute and chronic pain in bowel obstruction (BO). While clustered contractions and associated increase of intraluminal pressure may account for colicky pain in simple obstruction, ischemia may be involved in acute pain in severe conditions such as closed loop obstruction. Recent preclinical studies discovered that visceral sensitivity is increased in BO, and visceral hypersensitivity may underlie the mechanisms of chronic abdominal pain in BO. Mounting evidence suggests that lumen distension, as a circumferential mechanical stretch, alters gene expression (mechano-transcription) in the distended bowel, and mechano-transcription of nociceptive and inflammatory mediators plays a critical role in the development of visceral hypersensitivity in BO. Mechano-transcription of nerve growth factor (NGF) in gut smooth muscle cells is found to increase voltage-gated Na+ channel (Nav) activity of the primary sensory neurons by up-regulating expression of TTX-resistant Nav1.8, whereas mechanical stretch-induced brain-derived neurotrophic factor (BDNF) reduces Kv currents especially A-type (IA) currents by down-regulating expression of specific IA subtypes such as Kv1.4. The NGF and BDNF mediated changes in gene expression and channel functions in the primary sensory neurons may constitute the main mechanisms of visceral hypersensitivity in OBD. In addition, mechanical stretch-induced COX-2 and other inflammatory mediators in the gut may also contribute to abdominal pain by activating and sensitizing nociceptors.

High-Efficiency Electron Source with a Hollow Cathode in Technologies of Thin Film Deposition and Surface Treatment under Forevacuum Pressures

It is shown that low-energy beams with a high efficiency in a wide range of beam currents can be obtained in electron sources with a hollow cathode in the forevacuum pressure range. By varying the geometrical parameters of the electrode system and electromagnetic optics of the electron source, we succeeded in reaching the efficiency at a level of 0.9 for an accelerating potential of 1 kV and beam currents from 100 to 300 mA. The parameters affecting most strongly the efficiency and stability of operation of the electron source with a hollow cathode have been determined.

Neurotropin inhibits neuronal activity through potentiation of sustained Kv currents in primary cultured DRG neurons

Neurotropin (NTP) is a Japanese analgesic agent for treating neuropathic pain; however, its method of action remains unclear. This study examined the effects of NTP on the activity of small dorsal root ganglion (DRG) neurons using whole-cell patch clamp recordings. After 3 days of treatment, NTP decreased current injection-induced firing activity of cultured DRG neurons by raising the current threshold for action potential generation. Additionally, NTP increased the sustained component of voltage-gated potassium (Kv) channel currents without affecting other K+ currents. These results suggest that NTP inhibits the firing activity of DRG neurons through augmentation of sustained Kv current.