Salidroside modulates repolarization through stimulating Kv2.1 in rats.

BACKGROUND: Voltage-gated potassium (Kv) channel growth is strongly associated with the development of arrhythmia. Salidroside (Sal), an active component from Rhodiola crenulata, has been shown to exert protective effects against heart disease. The present study was conducted to investigate the effects of Sal on Kv2.1 channel, and to explore the ionic mechanism of anti-arrhythmic. METHODS: In this study, we utilized cisapride (Cis., A stimulant that prolongs the QT interval and causes cardiac arrhythmias) by intravenous injection to establish an arrhythmia model, and detected the effects of Sal on electrocardiography (ECG) and pressure volume loop (P-V loop) in SD rats. The effect of Sal on ECG of citalopram (Cit., a Kv2 channel inhibition)-evoked arrhythmia rat models was further evaluated by monitoring the dynamic changes of multiple indicators of ECG. Then, we detected the effect of Sal on the viability of hypoxic H9c2 cells using CCK-8 assay. After that, the effect of Sal on Kv channel currents (IKv) and Kv2.1 channel currents (IKv2.1) in H9c2 cells under normal and hypoxic conditions was examined using whole-cell patch clamp technique. In addition, the effect of Sal on IKv and IKv2.1 in H9c2 cells was determined under the inhibition of Kv and Kv2.1 channels. HEK293 cells stably transfected with Kv2.1 plasmids were also used to investigate the IKv2.1 changes under Sal pre-treated and co-incubated conditions. In addition, potential interactions of Sal with Kv2.1 protein were predicted and tested by molecular docking, molecular dynamics simulation (MDS), localized surface plasmon resonance (LSPR), and cellular thermal shift assay (CETSA) techniques, respectively. Furthermore, gene and protein levels of Kv2.1 in Sal-treated H9c2 cell were estimated by qRT-PCR, Western blot (WB) and immunofluorescence (IF) analysis. RESULTS: Sal shortened the prolongated QT interval and ameliorated the cardiac impairment associated with arrhythmia in SD rats caused by Cis., as reflected in the ECG and P-V loop data. And Sal was also protective against arrhythmia in rats caused by Kv2 channel inhibition. At the cellular level, Sal increased cell viability after CoCl2-induced hypoxic injury in H9c2 cells. Whole-cell patch clamp assay confirmed that Sal inhibited both IKv and IKv2.1 in normal H9c2 cells, while enhanced IKv and IKv2.1 in cardiomyocytes after hypoxic injury. And Sal enhanced IKv inhibited by 1.5 mM 4-AP and upregulated all inhibition of Kv2 channels induced by 20 mM 4-AP administration, antagonized the IKv2.1 inhibitory effect of Cit. Moreover, Sal pre-administration for 24 h and immediate administration increased IKv2.1 in HEK293 cells stably transfected with Kv2.1 plasmids. Molecular docking demonstrated the potential binding of Sal to the Kv2.1 protein, with calculated binding energy of -5.4 kcal/mol. MDS test illustrated that the average hydrogen bonding of the Sal-Kv2.1 complexes was 30.89%. LSPR results verified the potential binding of Sal to Kv2.1 protein with an affinity value of 9.95 × 10-4 M. CETSA assay confirmed Sal can enhance the expression of Kv2.1 protein in H9c2 cells treated with heat, which suggests that Sal may bind to Kv2.1 protein. The results of WB, qRT-PCR, and IF further argued that Sal pre-administration for 24 h enhanced the levels of the Kv2.1 gene and protein (with no effects on the Kv2.1 gene and protein for H9c2 cells co-incubated with Sal for 6 h and 12 h). CONCLUSION: Overall, our findings indicate that Sal can resist drug-induced arrhythmias in SD rats, partially by modulating repolarization through stimulating Kv2.1.

One-shot design elevates functional expression levels of a voltage-gated potassium channel.

Membrane proteins play critical physiological roles as receptors, channels, pumps, and transporters. Despite their importance, however, low expression levels often hamper the experimental characterization of membrane proteins. We present an automated and web-accessible design algorithm called mPROSS (https://mPROSS.weizmann.ac.il), which uses phylogenetic analysis and an atomistic potential, including an empirical lipophilicity scale, to improve native-state energy. As a stringent test, we apply mPROSS to the Kv1.2-Kv2.1 paddle chimera voltage-gated potassium channel. Four designs, encoding 9-26 mutations relative to the parental channel, were functional and maintained potassium-selective permeation and voltage dependence in Xenopus oocytes with up to 14-fold increase in whole-cell current densities. Additionally, single-channel recordings reveal no significant change in the channel-opening probability nor in unitary conductance, indicating that functional expression levels increase without impacting the activity profile of individual channels. Our results suggest that the expression levels of other dynamic channels and receptors may be enhanced through one-shot design calculations.

Mono-allelic KCNB2 variants lead to a neurodevelopmental syndrome caused by altered channel inactivation.

Ion channels mediate voltage fluxes or action potentials that are central to the functioning of excitable cells such as neurons. The KCNB family of voltage-gated potassium channels (Kv) consists of two members (KCNB1 and KCNB2) encoded by KCNB1 and KCNB2, respectively. These channels are major contributors to delayed rectifier potassium currents arising from the neuronal soma which modulate overall excitability of neurons. In this study, we identified several mono-allelic pathogenic missense variants in KCNB2, in individuals with a neurodevelopmental syndrome with epilepsy and autism in some individuals. Recurrent dysmorphisms included a broad forehead, synophrys, and digital anomalies. Additionally, we selected three variants where genetic transmission has not been assessed, from two epilepsy studies, for inclusion in our experiments. We characterized channel properties of these variants by expressing them in oocytes of Xenopus laevis and conducting cut-open oocyte voltage clamp electrophysiology. Our datasets indicate no significant change in absolute conductance and conductance-voltage relationships of most disease variants as compared to wild type (WT), when expressed either alone or co-expressed with WT-KCNB2. However, variants c.1141A>G (p.Thr381Ala) and c.641C>T (p.Thr214Met) show complete abrogation of currents when expressed alone with the former exhibiting a left shift in activation midpoint when expressed alone or with WT-KCNB2. The variants we studied, nevertheless, show collective features of increased inactivation shifted to hyperpolarized potentials. We suggest that the effects of the variants on channel inactivation result in hyper-excitability of neurons, which contributes to disease manifestations.

Discovery of 2-Ethoxy-5-isobutyramido-N-1-substituted Benzamide Derivatives as Selective Kv2.1 Inhibitors with In Vivo Neuroprotective Effects.

Kv2.1 is involved in regulating neuronal excitability and neuronal cell apoptosis, and inhibiting Kv2.1 is a potential strategy to prevent cell death and achieve neuroprotection in ischemic stroke. In this work, a series of novel benzamide derivatives were designed and synthesized as Kv2.1 inhibitors, and extensive structure-activity relationships led to highly potent and selective Kv2.1 inhibitors having IC50 values of 10-8 M. Among them, compound 80 (IC50 = 0.07 µM, selectivity >130 fold over other K+, Na+, and Ca2+ ion channels) was able to decrease the apoptosis of HEK293/Kv2.1 cells induced by H2O2. Furthermore, its anti-ischemic efficacy was demonstrated as it markedly reduced the infarct volume in MCAO rat model. Additionally, compound 80 possessed appropriate plasma PK parameters. It could serve as a probe to investigate Kv2.1 pathological functions and deserved to be further explored.

The formation of KV2.1 macro-clusters is required for sex-specific differences in L-type CaV1.2 clustering and function in arterial myocytes.

In arterial myocytes, the canonical function of voltage-gated CaV1.2 and KV2.1 channels is to induce myocyte contraction and relaxation through their responses to membrane depolarization, respectively. Paradoxically, KV2.1 also plays a sex-specific role by promoting the clustering and activity of CaV1.2 channels. However, the impact of KV2.1 protein organization on CaV1.2 function remains poorly understood. We discovered that KV2.1 forms micro-clusters, which can transform into large macro-clusters when a critical clustering site (S590) in the channel is phosphorylated in arterial myocytes. Notably, female myocytes exhibit greater phosphorylation of S590, and macro-cluster formation compared to males. Contrary to current models, the activity of KV2.1 channels seems unrelated to density or macro-clustering in arterial myocytes. Disrupting the KV2.1 clustering site (KV2.1S590A) eliminated KV2.1 macro-clustering and sex-specific differences in CaV1.2 cluster size and activity. We propose that the degree of KV2.1 clustering tunes CaV1.2 channel function in a sex-specific manner in arterial myocytes.

An in silico investigation of Kv2.1 potassium channel: Model building and inhibitors binding sites analysis.

Kv2.1 is widely expressed in brain, and inhibiting Kv2.1 is a potential strategy to prevent cell death and achieve neuroprotection in ischemic stroke. Herein, an in silico model of Kv2.1 tetramer structure was constructed by employing the AlphaFold-Multimer deep learning method to facilitate the rational discovery of Kv2.1 inhibitors. GaMD was utilized to create an ion transporting trajectory, which was analyzed with HMM to generate multiple representative receptor conformations. The binding site of RY785 and RY796(S) under the P-loop was defined with Fpocket program together with the competitive binding electrophysiology assay. The docking poses of the two inhibitors were predicted with the aid of the semi-empirical quantum mechanical calculation, and the IGMH results suggested that Met375, Thr376, and Thr377 of the P-helix and Ile405 of the S6 segment made significant contributions to the binding affinity. These results provided insights for rational molecular design to develop novel Kv2.1 inhibitors.

Inactivation of the Kv2.1 channel through electromechanical coupling.

The Kv2.1 voltage-activated potassium (Kv) channel is a prominent delayed-rectifier Kv channel in the mammalian central nervous system, where its mechanisms of activation and inactivation are critical for regulating intrinsic neuronal excitability1,2. Here we present structures of the Kv2.1 channel in a lipid environment using cryo-electron microscopy to provide a framework for exploring its functional mechanisms and how mutations causing epileptic encephalopathies3-7 alter channel activity. By studying a series of disease-causing mutations, we identified one that illuminates a hydrophobic coupling nexus near the internal end of the pore that is critical for inactivation. Both functional and structural studies reveal that inactivation in Kv2.1 results from dynamic alterations in electromechanical coupling to reposition pore-lining S6 helices and close the internal pore. Consideration of these findings along with available structures for other Kv channels, as well as voltage-activated sodium and calcium channels, suggests that related mechanisms of inactivation are conserved in voltage-activated cation channels and likely to be engaged by widely used therapeutics to achieve state-dependent regulation of channel activity.

Kv2.1 Channels Prevent Vasomotion and Safeguard Myogenic Reactivity in Rat Small Superior Cerebellar Arteries.

Vascular smooth muscle voltage-gated potassium (Kv) channels have been proposed to contribute to myogenic autoregulation. Surprisingly, in initial experiments, we observed that the Kv2 channel inhibitor stromatoxin induced vasomotion without affecting myogenic tone. Thus, we tested the hypothesis that Kv2 channels contribute to myogenic autoregulation by fine-tuning the myogenic response. Expression of Kv2 channel mRNA was determined using real-time PCR and 'multiplex' single-cell RT-PCR. Potassium currents were measured using the patch-clamp technique. Contractile responses of intact arteries were studied using isobaric myography. Expression of Kv2.1 but not Kv2.2 channels was detected in intact rat superior cerebellar arteries and in single smooth muscle cells. Stromatoxin, a high-affinity inhibitor of Kv2 channels, reduced smooth muscle Kv currents by 61% at saturating concentrations (EC50 36 nmol/L). Further, stromatoxin (10-100 nmol/L) induced pronounced vasomotion in 48% of the vessels studied. In vessels not exhibiting vasomotion, stromatoxin did not affect myogenic reactivity. Notably, in vessels exhibiting stromatoxin-induced vasomotion, pressure increases evoked two effects: First, they facilitated the occurrence of random vasodilations and/or vasoconstrictions, disturbing the myogenic response (24% of the vessels). Second, they modified the vasomotion by decreasing its amplitude and increasing its frequency, thereby destabilizing myogenic tone (76% of the vessels). Our study demonstrates that (i) Kv2.1 channels are the predominantly expressed Kv channels in smooth muscle cells of rat superior cerebellar arteries, and (ii) Kv2.1 channels provide a novel type of negative feedback mechanism in myogenic autoregulation by preventing vasomotion and thereby safeguarding the myogenic response.

Increased KV2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K+ Currents in Hippocampal Neurons of the Tg2576 Alzheimer's Disease Mouse.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Cortical and hippocampal hyperexcitability intervenes in the pathological derangement of brain activity leading to cognitive decline. As key regulators of neuronal excitability, the voltage-gated K+ channels (KV) might play a crucial role in the AD pathophysiology. Among them, the KV2.1 channel, the main α subunit mediating the delayed rectifier K+ currents (IDR) and controlling the intrinsic excitability of pyramidal neurons, has been poorly examined in AD. In the present study, we investigated the KV2.1 protein expression and activity in hippocampal neurons from the Tg2576 mouse, a widely used transgenic model of AD. To this aim we performed whole-cell patch-clamp recordings, Western blotting, and immunofluorescence analyses. Our Western blotting results reveal that KV2.1 was overexpressed in the hippocampus of 3-month-old Tg2576 mice and in primary hippocampal neurons from Tg2576 mouse embryos compared with the WT counterparts. Electrophysiological experiments unveiled that the whole IDR were reduced in the Tg2576 primary neurons compared with the WT neurons, and that this reduction was due to the loss of the KV2.1 current component. Moreover, we found that the reduction of the KV2.1-mediated currents was due to increased channel clustering, and that glutamate, a stimulus inducing KV2.1 declustering, was able to restore the IDR to levels comparable to those of the WT neurons. These findings add new information about the dysregulation of ionic homeostasis in the Tg2576 AD mouse model and identify KV2.1 as a possible player in the AD-related alterations of neuronal excitability.

Activity-dependent endoplasmic reticulum Ca2+ uptake depends on Kv2.1-mediated endoplasmic reticulum/plasma membrane junctions to promote synaptic transmission.

The endoplasmic reticulum (ER) forms a continuous and dynamic network throughout a neuron, extending from dendrites to axon terminals, and axonal ER dysfunction is implicated in several neurological disorders. In addition, tight junctions between the ER and plasma membrane (PM) are formed by several molecules including Kv2 channels, but the cellular functions of many ER-PM junctions remain unknown. Recently, dynamic Ca2+ uptake into the ER during electrical activity was shown to play an essential role in synaptic transmission. Our experiments demonstrate that Kv2.1 channels are necessary for enabling ER Ca2+ uptake during electrical activity, as knockdown (KD) of Kv2.1 rendered both the somatic and axonal ER unable to accumulate Ca2+ during electrical stimulation. Moreover, our experiments demonstrate that the loss of Kv2.1 in the axon impairs synaptic vesicle fusion during stimulation via a mechanism unrelated to voltage. Thus, our data demonstrate that a nonconducting role of Kv2.1 exists through its binding to the ER protein VAMP-associated protein (VAP), which couples ER Ca2+ uptake with electrical activity. Our results further suggest that Kv2.1 has a critical function in neuronal cell biology for Ca2+ handling independent of voltage and reveals a critical pathway for maintaining ER lumen Ca2+ levels and efficient neurotransmitter release. Taken together, these findings reveal an essential nonclassical role for both Kv2.1 and the ER-PM junctions in synaptic transmission.

A Kv2 inhibitor traps itself in place.

Voltage activation, but not channel opening, is required for RY785 to access the central cavity of Kv2 channels, where it promotes voltage sensor deactivation to trap itself in place.

Mechanism of use-dependent Kv2 channel inhibition by RY785.

Understanding the mechanism by which ion channel modulators act is critical for interpretation of their physiological effects and can provide insight into mechanisms of ion channel gating. The small molecule RY785 is a potent and selective inhibitor of Kv2 voltage-gated K+ channels that has a use-dependent onset of inhibition. Here, we investigate the mechanism of RY785 inhibition of rat Kv2.1 (Kcnb1) channels heterologously expressed in CHO-K1 cells. We find that 1 µM RY785 block eliminates Kv2.1 current at all physiologically relevant voltages, inhibiting ≥98% of the Kv2.1 conductance. Both onset of and recovery from RY785 inhibition require voltage sensor activation. Intracellular tetraethylammonium, a classic open-channel blocker, competes with RY785 inhibition. However, channel opening itself does not appear to alter RY785 access. Gating current measurements reveal that RY785 inhibits a component of voltage sensor activation and accelerates voltage sensor deactivation. We propose that voltage sensor activation opens a path into the central cavity of Kv2.1 where RY785 binds and promotes voltage sensor deactivation, trapping itself inside. This gated-access mechanism in conjunction with slow kinetics of unblock supports simple interpretation of RY785 effects: channel activation is required for block by RY785 to equilibrate, after which trapped RY785 will simply decrease the Kv2 conductance density.

Cleavage of Kv2.1 by BACE1 decreases potassium current and reduces neuronal apoptosis.

As an aspartic protease, ß-site APP cleaving enzyme 1 (BACE1) can efficiently cleave amyloid precursor protein (APP) to produce amyloid beta (Aß), a chief constituent of senile plaques in Alzheimer's disease. Thus, BACE1 inhibitor is identified as a therapeutic candidate for AD. However, recent failures of clinical trials using BACE1 inhibitors emphasized that comprehensively understanding of BACE1 function is particularly important. Kv2.1, a potassium channel, modulates potassium current in cortical neurons and potassium efflux is a requisite event in the process of cell apoptosis. Previously we showed that BACE2 cleaves Kv2.1 and reduces neuronal apoptosis. Our study here showed that BACE1 cleaves Kv2.1, and results in decreased Ik of Kv2.1. Furthermore, we demonstrated that the BACE1-cleaved Kv2.1 reduces neuronal apoptosis and BACE1 inhibitor markedly increases neuronal apoptosis. Our work indicates that BACE1 plays a neuroprotective role to reduce potassium efflux by cleavage of Kv2.1, implying inhibition of BACE1 may be neurotoxic.

The AMIGO1 adhesion protein activates Kv2.1 voltage sensors.

Kv2 voltage-gated potassium channels are modulated by amphoterin-induced gene and open reading frame (AMIGO) neuronal adhesion proteins. Here, we identify steps in the conductance activation pathway of Kv2.1 channels that are modulated by AMIGO1 using voltage-clamp recordings and spectroscopy of heterologously expressed Kv2.1 and AMIGO1 in mammalian cell lines. AMIGO1 speeds early voltage-sensor movements and shifts the gating charge-voltage relationship to more negative voltages. The gating charge-voltage relationship indicates that AMIGO1 exerts a larger energetic effect on voltage-sensor movement than is apparent from the midpoint of the conductance-voltage relationship. When voltage sensors are detained at rest by voltage-sensor toxins, AMIGO1 has a greater impact on the conductance-voltage relationship. Fluorescence measurements from voltage-sensor toxins bound to Kv2.1 indicate that with AMIGO1, the voltage sensors enter their earliest resting conformation, yet this conformation is less stable upon voltage stimulation. We conclude that AMIGO1 modulates the Kv2.1 conductance activation pathway by destabilizing the earliest resting state of the voltage sensors.

High spatial density is associated with non-conducting Kv channels from two families.

Ion channels are well known for their ability to regulate the cell membrane potential. However, many ion channels also have functions that do not involve ion conductance. Kv2 channels are one family of ion channels whose non-conducting functions are central to mammalian cell physiology. Kv2.1 and Kv2.2 channels form stable contact sites between the endoplasmic reticulum and plasma membrane via an interaction with endoplasmic reticulum resident proteins. To perform this structural role, Kv2 channels are expressed at extremely high densities on the plasma membranes of many cell types, including central pyramidal neurons, α-motoneurons, and smooth muscle cells. Research from our lab and others has shown that the majority of these plasma membrane Kv2.1 channels do not conduct potassium in response to depolarization. The mechanism of this channel silencing is unknown but is thought to be dependent on channel density in the membrane. Furthermore, the prevalence of a non-conducting population of Kv2.2 channels has not been directly tested. In this work we make improved measurements of the numbers of conducting and non-conducting Kv2.1 channels expressed in HEK293 cells and expand the investigation of non-conducting channels to three additional Kv α-subunits: Kv2.2, Kv1.4, and Kv1.5. By comparing the numbers of gating and conducting channels in individual HEK293 cells, we found that on average, only 50% of both Kv2.1 and Kv2.2 channels conducted potassium and, as previously suggested, that fraction decreased with increased channel density in the plasma membrane. At the highest spatial densities tested, which are comparable with those found at Kv2 clusters in situ, only 20% of Kv2.1 and Kv2.2 channels conducted potassium. We also show for the first time that Kv1.4 and Kv1.5 exhibit density-dependent silencing, suggesting that this phenomenon has an underlying mechanism that is shared by Kv channels from multiple families.

Kv2.1 Potassium Channels Regulate Repetitive Burst Firing in Extratelencephalic Neocortical Pyramidal Neurons.

Coincidence detection and cortical rhythmicity are both greatly influenced by neurons' propensity to fire bursts of action potentials. In the neocortex, repetitive burst firing can also initiate abnormal neocortical rhythmicity (including epilepsy). Bursts are generated by inward currents that underlie a fast afterdepolarization (fADP) but less is known about outward currents that regulate bursting. We tested whether Kv2 channels regulate the fADP and burst firing in labeled layer 5 PNs from motor cortex of the Thy1-h mouse. Kv2 block with guangxitoxin-1E (GTx) converted single spike responses evoked by dendritic stimulation into multispike bursts riding on an enhanced fADP. Immunohistochemistry revealed that Thy1-h PNs expressed Kv2.1 (not Kv2.2) channels perisomatically (not in the dendrites). In somatic macropatches, GTx-sensitive current was the largest component of outward current with biophysical properties well-suited for regulating bursting. GTx drove ~40% of Thy1 PNs stimulated with noisy somatic current steps to repetitive burst firing and shifted the maximal frequency-dependent gain. A network model showed that reduction of Kv2-like conductance in a small subset of neurons resulted in repetitive bursting and entrainment of the circuit to seizure-like rhythmic activity. Kv2 channels play a dominant role in regulating onset bursts and preventing repetitive bursting in Thy1 PNs.

EVAP: A two-photon imaging tool to study conformational changes in endogenous Kv2 channels in live tissues.

A primary goal of molecular physiology is to understand how conformational changes of proteins affect the function of cells, tissues, and organisms. Here, we describe an imaging method for measuring the conformational changes of the voltage sensors of endogenous ion channel proteins within live tissue, without genetic modification. We synthesized GxTX-594, a variant of the peptidyl tarantula toxin guangxitoxin-1E, conjugated to a fluorophore optimal for two-photon excitation imaging through light-scattering tissue. We term this tool EVAP (Endogenous Voltage-sensor Activity Probe). GxTX-594 targets the voltage sensors of Kv2 proteins, which form potassium channels and plasma membrane-endoplasmic reticulum junctions. GxTX-594 dynamically labels Kv2 proteins on cell surfaces in response to voltage stimulation. To interpret dynamic changes in fluorescence intensity, we developed a statistical thermodynamic model that relates the conformational changes of Kv2 voltage sensors to degree of labeling. We used two-photon excitation imaging of rat brain slices to image Kv2 proteins in neurons. We found puncta of GxTX-594 on hippocampal CA1 neurons that responded to voltage stimulation and retain a voltage response roughly similar to heterologously expressed Kv2.1 protein. Our findings show that EVAP imaging methods enable the identification of conformational changes of endogenous Kv2 voltage sensors in tissue.

Kv2 channel-AMIGO ß-subunit assembly modulates both channel function and cell adhesion molecule surface trafficking.

The Kv2 channels encode delayed rectifier currents that regulate membrane potential in many tissues. They also have a non-conducting function to form stable junctions between the endoplasmic reticulum and plasma membranes, creating membrane contact sites that mediate functions distinct from membrane excitability. Therefore, proteins that interact with Kv2.1 and Kv2.2 channels can alter conducting and/or non-conducting channel properties. One member of the AMIGO family of proteins is an auxiliary ß-subunit for Kv2 channels and modulates Kv2.1 electrical activity. However, the AMIGO family has two additional members of ∼50% similarity that have not yet been characterized as Kv2 ß-subunits. In this work, we show that the surface trafficking and localization of all three AMIGOs are controlled by their assembly with both Kv2 channels. Additionally, assembly of each AMIGO with either Kv2.1 or Kv2.2 hyperpolarizes the channel activation midpoint by -10 mV. However, only AMIGO2 significantly slows inactivation and deactivation, leading to a prolonged open state of Kv2 channels. The co-regulatory effects of Kv2s and AMIGOs likely fine-tune both the electrical and non-electrical properties of the cells in which they are expressed.

Molecular, Cellular and Functional Changes in the Retinas of Young Adult Mice Lacking the Voltage-Gated K+ Channel Subunits Kv8.2 and K2.1.

Cone Dystrophy with Supernormal Rod Response (CDSRR) is a rare autosomal recessive disorder leading to severe visual impairment in humans, but little is known about its unique pathophysiology. We have previously shown that CDSRR is caused by mutations in the KCNV2 (Potassium Voltage-Gated Channel Modifier Subfamily V Member 2) gene encoding the Kv8.2 subunit, a modulatory subunit of voltage-gated potassium (Kv) channels. In a recent study, we validated a novel mouse model of Kv8.2 deficiency at a late stage of the disease and showed that it replicates the human electroretinogram (ERG) phenotype. In this current study, we focused our investigation on young adult retinas to look for early markers of disease and evaluate their effect on retinal morphology, electrophysiology and immune response in both the Kv8.2 knockout (KO) mouse and in the Kv2.1 KO mouse, the obligate partner of Kv8.2 in functional retinal Kv channels. By evaluating the severity of retinal dystrophy in these KO models, we demonstrated that retinas of Kv KO mice have significantly higher apoptotic cells, a thinner outer nuclear cell layer and increased activated microglia cells in the subretinal space. Our results indicate that in the murine retina, the loss of Kv8.2 subunits contributes to early cellular and physiological changes leading to retinal dysfunction. These results could have potential implications in the early management of CDSRR despite its relatively nonprogressive nature in humans.

Inhibition of voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells by the class Ic antiarrhythmic agent lorcainide.

Voltage-dependent K+ (Kv) channels play the role of returning the membrane potential to the resting state, thereby maintaining the vascular tone. Here, we used native smooth-muscle cells from rabbit coronary arteries to investigate the inhibitory effect of lorcainide, a class Ic antiarrhythmic agent, on Kv channels. Lorcainide inhibited Kv channels in a concentration-dependent manner with an IC50 of 4.46 ± 0.15 µM and a Hill coefficient of 0.95 ± 0.01. Although application of lorcainide did not change the activation curve, it shifted the inactivation curve toward a more negative potential, implying that lorcainide inhibits Kv channels by changing the channels' voltage sensors. The recovery time constant from channel inactivation increased in the presence of lorcainide. Furthermore, application of train steps (of 1 or 2 Hz) in the presence of lorcainide progressively augmented the inhibition of Kv currents, implying that lorcainide-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with Kv1.5 or Kv2.1/2.2 inhibitors effectively reduced the amplitude of the Kv current but did not affect the inhibitory effect of lorcainide. Based on these results, we conclude that lorcainide inhibits vascular Kv channels in a concentration and use (state)-dependent manner by changing their inactivation gating properties. Considering the clinical efficacy of lorcainide, and the pathophysiological significance of vascular Kv channels, our findings should be considered when prescribing lorcainide to patients with arrhythmia and vascular disease.