An activator of voltage-gated K+ channels Kv1.1 as a therapeutic candidate for episodic ataxia type 1.

Loss-of-function mutations in the KCNA1(Kv1.1) gene cause episodic ataxia type 1 (EA1), a neurological disease characterized by cerebellar dysfunction, ataxic attacks, persistent myokymia with painful cramps in skeletal muscles, and epilepsy. Precision medicine for EA1 treatment is currently unfeasible, as no drug that can enhance the activity of Kv1.1-containing channels and offset the functional defects caused by KCNA1 mutations has been clinically approved. Here, we uncovered that niflumic acid (NFA), a currently prescribed analgesic and anti-inflammatory drug with an excellent safety profile in the clinic, potentiates the activity of Kv1.1 channels. NFA increased Kv1.1 current amplitudes by enhancing the channel open probability, causing a hyperpolarizing shift in the voltage dependence of both channel opening and gating charge movement, slowing the OFF-gating current decay. NFA exerted similar actions on both homomeric Kv1.2 and heteromeric Kv1.1/Kv1.2 channels, which are formed in most brain structures. We show that through its potentiating action, NFA mitigated the EA1 mutation-induced functional defects in Kv1.1 and restored cerebellar synaptic transmission, Purkinje cell availability, and precision of firing. In addition, NFA ameliorated the motor performance of a knock-in mouse model of EA1 and restored the neuromuscular transmission and climbing ability in Shaker (Kv1.1) mutant Drosophila melanogaster flies (Sh5). By virtue of its multiple actions, NFA has strong potential as an efficacious single-molecule-based therapeutic agent for EA1 and serves as a valuable model for drug discovery.

Functional Epicardial Conduction Disturbances Due to a SCN5A Variant Associated With Brugada Syndrome.

BACKGROUND: Brugada syndrome is a significant cause of sudden cardiac death (SCD), but the underlying mechanisms remain hypothetical. OBJECTIVES: This study aimed to elucidate this knowledge gap through detailed ex vivo human heart studies. METHODS: A heart was obtained from a 15-year-old adolescent boy with normal electrocardiogram who experienced SCD. Postmortem genotyping was performed, and clinical examinations were done on first-degree relatives. The right ventricle was optically mapped, followed by high-field magnetic resonance imaging and histology. Connexin-43 and NaV1.5 were localized by immunofluorescence, and RNA and protein expression levels were studied. HEK-293 cell surface biotinylation assays were performed to examine NaV1.5 trafficking. RESULTS: A Brugada-related SCD diagnosis was established for the donor because of a SCN5A Brugada-related variant (p.D356N) inherited from his mother, together with a concomitant NKX2.5 variant of unknown significance. Optical mapping demonstrated a localized epicardial region of impaired conduction near the outflow tract, in the absence of repolarization alterations and microstructural defects, leading to conduction blocks and figure-of-8 patterns. NaV1.5 and connexin-43 localizations were normal in this region, consistent with the finding that the p.D356N variant does not affect the trafficking, nor the expression of NaV1.5. Trends of decreased NaV1.5, connexin-43, and desmoglein-2 protein levels were noted; however, the RT-qPCR results suggested that the NKX2-5 variant was unlikely to be involved. CONCLUSIONS: This study demonstrates for the first time that SCD associated with a Brugada-SCN5A variant can be caused by localized functionally, not structurally, impaired conduction.

Regional Differences in Ca2+ Signaling and Transverse-Tubules across Left Atrium from Adult Sheep.

Cardiac excitation-contraction coupling can be different between regions of the heart. Little is known at the atria level, specifically in different regions of the left atrium. This is important given the role of cardiac myocytes from the pulmonary vein sleeves, which are responsible for ectopic activity during atrial fibrillation. In this study, we present a new method to isolate atrial cardiac myocytes from four different regions of the left atrium of a large animal model, sheep, highly relevant to humans. Using collagenase/protease we obtained calcium-tolerant atrial cardiac myocytes from the epicardium, endocardium, free wall and pulmonary vein regions. Calcium transients were slower (time to peak and time to decay) in free wall and pulmonary vein myocytes compared to the epicardium and endocardium. This is associated with lower t-tubule density. Overall, these results suggest regional differences in calcium transient and t-tubule density across left atria, which may play a major role in the genesis of atrial fibrillation.

NMDA-Type Glutamate Receptor Activation Promotes Vascular Remodeling and Pulmonary Arterial Hypertension.

BACKGROUND: Excessive proliferation and apoptosis resistance in pulmonary vascular cells underlie vascular remodeling in pulmonary arterial hypertension (PAH). Specific treatments for PAH exist, mostly targeting endothelial dysfunction, but high pulmonary arterial pressure still causes heart failure and death. Pulmonary vascular remodeling may be driven by metabolic reprogramming of vascular cells to increase glutaminolysis and glutamate production. The N-methyl-d-aspartate receptor (NMDAR), a major neuronal glutamate receptor, is also expressed on vascular cells, but its role in PAH is unknown. METHODS: We assessed the status of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and controls through mass spectrometry imaging, Western blotting, and immunohistochemistry. We measured the glutamate release from cultured pulmonary vascular cells using enzymatic assays and analyzed NMDAR regulation/phosphorylation through Western blot experiments. The effect of NMDAR blockade on human pulmonary arterial smooth muscle cell proliferation was determined using a BrdU incorporation assay. We assessed the role of NMDARs in vascular remodeling associated to pulmonary hypertension, in both smooth muscle-specific NMDAR knockout mice exposed to chronic hypoxia and the monocrotaline rat model of pulmonary hypertension using NMDAR blockers. RESULTS: We report glutamate accumulation, upregulation of the NMDAR, and NMDAR engagement reflected by increases in GluN1-subunit phosphorylation in the pulmonary arteries of human patients with PAH. Kv channel inhibition and type A-selective endothelin receptor activation amplified calcium-dependent glutamate release from human pulmonary arterial smooth muscle cell, and type A-selective endothelin receptor and platelet-derived growth factor receptor activation led to NMDAR engagement, highlighting crosstalk between the glutamate-NMDAR axis and major PAH-associated pathways. The platelet-derived growth factor-BB-induced proliferation of human pulmonary arterial smooth muscle cells involved NMDAR activation and phosphorylated GluN1 subunit localization to cell-cell contacts, consistent with glutamatergic communication between proliferating human pulmonary arterial smooth muscle cells via NMDARs. Smooth-muscle NMDAR deficiency in mice attenuated the vascular remodeling triggered by chronic hypoxia, highlighting the role of vascular NMDARs in pulmonary hypertension. Pharmacological NMDAR blockade in the monocrotaline rat model of pulmonary hypertension had beneficial effects on cardiac and vascular remodeling, decreasing endothelial dysfunction, cell proliferation, and apoptosis resistance while disrupting the glutamate-NMDAR pathway in pulmonary arteries. CONCLUSIONS: These results reveal a dysregulation of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and identify vascular NMDARs as targets for antiremodeling treatments in PAH.

Acute stress causes rapid synaptic insertion of Ca2+ -permeable AMPA receptors to facilitate long-term potentiation in the hippocampus.

The neuroendocrine response to episodes of acute stress is crucial for survival whereas the prolonged response to chronic stress can be detrimental. Learning and memory are particularly susceptible to stress with cognitive deficits being well characterized consequences of chronic stress. Although there is good evidence that acute stress can enhance cognitive performance, the mechanism(s) for this are unclear. We find that hippocampal slices, either prepared from rats following 30 min restraint stress or directly exposed to glucocorticoids, exhibit an N-methyl-d-aspartic acid receptor-independent form of long-term potentiation. We demonstrate that the mechanism involves an NMDA receptor and PKA-dependent insertion of Ca2+ -permeable AMPA receptors into synapses. These then trigger the additional NMDA receptor-independent form of LTP during high frequency stimulation.

Stepwise, non-adherent differentiation of human pluripotent stem cells to generate basal forebrain cholinergic neurons via hedgehog signaling.

Basal forebrain cholinergic neurons (bfCNs) which provide innervation to the hippocampus and cortex, are required for memory and learning, and are primarily affected in Alzheimer's Disease (AD), resulting in related cognitive decline. Therefore generation of a source of bfCNs from human pluripotent stem cells (hPSCs) is crucial for in vitro disease modeling and development of novel AD therapies. In addition, for the advancement of regenerative approaches there is a requirement for an accurate developmental model to study the neurogenesis and survival of this population. Here we demonstrate the efficient production of bfCNs, using a novel embryoid body (EB) based non-adherent differentiation (NAdD) protocol. We establish a specific basal forebrain neural stem cell (NSC) phenotype via expression of the basal forebrain transcription factors NKX2.1 and LHX8, as well as the general forebrain marker FOXG1. We present evidence that this lineage is achieved via recapitulation of embryonic events, with induction of intrinsic hedgehog signaling, through the use of a 3D non-adherent differentiation system. This is the first example of hPSC-derived basal forebrain-like NSCs, which are scalable via self-renewal in prolonged culture. Furthermore upon terminal differentiation these basal forebrain-like NSCs generate high numbers of cholinergic neurons expressing the specific markers ChAT, VACht and ISL1. These hPSC-derived bfCNs possess characteristics that are crucial in a model to study AD related cholinergic neuronal loss in the basal forebrain. Examples are expression of the therapeutic target p75(NTR), the release of acetylcholine, and demonstration of a mature, and functional electrophysiological profile. In conclusion, this work provides a renewable source of human functional bfCNs applicable for studying AD specifically in the cholinergic system, and also provides a model of the key embryonic events in human bfCN development.

Characterization of the tissue-level Ca2+ signals in spontaneously contracting human myometrium.

In the labouring uterus, millions of myocytes forming the complex geometrical structure of myometrium contract in synchrony to increase intrauterine pressure, dilate the cervix and eventually expel the foetus through the birth canal. The mechanisms underlying the precise coordination of contractions in human myometrium are not completely understood. In the present study, we have characterized the spatio-temporal properties of tissue-level [Ca(2+)](i) transients in thin slices of intact human myometrium. We found that the waveform of [Ca(2+)](i) transients and isotonic contractions recorded from thin slices was similar to the waveform of isometric contractions recorded from the larger strips in traditional organ bath experiments, suggesting that the spatio-temporal information obtained from thin slices is representative of the whole tissue. By comparing the time course of [Ca(2+)](i) transients in individual cells to that recorded from the bundles of myocytes we found that the majority of myocytes produce rapidly propagating long-lasting [Ca(2+)](i) transients accompanied by contractions. We also found a small number of cells showing desynchronized [Ca(2+)](i) oscillations that did not trigger contractions. The [Ca(2+)](i) oscillations in these cells were insensitive to nifedipine, but readily inhibited by the T-type Ca(2+) channel inhibitor NNC55-0396. In conclusion, our data suggest that the spread of [Ca(2+)](i) signals in human myometrium is achieved via propagation of long-lasting action potentials. The propagation was fast when action potentials propagated along bundles of myocytes and slower when propagating between the bundles of uterine myocytes.

Aß(1-42) inhibition of LTP is mediated by a signaling pathway involving caspase-3, Akt1 and GSK-3ß.

Amyloid-ß(1-42) (Aß) is thought to be a major mediator of the cognitive deficits in Alzheimer's disease. The ability of Aß to inhibit hippocampal long-term potentiation provides a cellular correlate of this action, but the underlying molecular mechanism is only partially understood. We found that a signaling pathway involving caspase-3, Akt1 and glycogen synthase kinase-3ß is an important mediator of this effect in rats and mice.

Characterization of the molecular and electrophysiological properties of the T-type calcium channel in human myometrium.

Rises in intracellular calcium are essential for contraction of human myometrial smooth muscle (HMSM) and hence parturition. The T-type calcium channel may play a role in this process. The aim was to investigate the role of the T-type calcium channel in HMSM by characterizing mRNA expression, protein localization, electrophysiological properties and function of the channel subunits Cav3.1(alpha1G), Cav3.2(alpha1H), and Cav3.3(alpha1I). QRT-PCR, immunohistochemistry, electrophysiology and invitro contractility were performed on human myometrial samples from term, preterm, labour and not in labour. QRT-PCR analysis of Cav3.1, Cav3.2 and Cav3.3 demonstrated expression of Cav3.1 and Cav3.2 with no significant change (P>0.05) associated with gestation or labour status. Immunohistochemistry localized Cav3.1 to myometrial and vascular smooth muscle cells whilst Cav3.2 localized to vascular endothelial cells and invading leucocytes. Voltage clamp studies demonstrated a T-type current in 55% of cells. Nickel block of T-type current was voltage sensitive (IC50 of 118.57+/-68.9 microM at -30 mV). Activation and inactivation curves of ICa currents in cells expressing T-type channels overlapped demonstrating steady state window currents at the resting membrane potential of myometrium at term. Current clamp analysis demonstrated that hyperpolarizing pulses to a membrane potential greater than -80 mV elicited rebound calcium spikes that were blocked reversibly by 100 microM nickel. Contractility studies demonstrated a reversible decrease in contraction frequency during application of 100 microM nickel (P<0.05). We conclude that the primary T-type subunit expressed in some MSMCs is Cav3.1. We found that application of 100 microM nickel to spontaneously contracting human myometrium reversibly slows contraction frequency.

Control of uterine Ca2+ by membrane voltage: toward understanding the excitation-contraction coupling in human myometrium.

Myometrial contractility is a complex and dynamic physiological process that changes substantially during pregnancy and culminates in childbirth. Uterine contractions are initiated by transient rises in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)), which in turn are triggered and controlled by myometrial action potentials. The sequence of events between the action potential generation and the contraction initiation is referred to as excitation-contraction coupling. Hormones and other physiologically active substances affect myometrial contractility by modulating different steps in the excitation-contraction coupling process. It is therefore imperative that we understand that process to understand the regulation of myometrial contractility. The complex action potentials generated by human myometrium result from the activity of many ion channels, transporters, and pumps. Two types of myometrial action potential waveform have been described in the literature: a plateau type and a spike type. Parameters of the myometrial [Ca(2+)](i) transients and contractions differ depending on the type of action potential that triggers them. Some aspects of the excitation-contraction coupling are unique to human myometrium and cannot be found in animal models; some others are common between many species. This article reviews the current state and discusses future directions of physiological research on human myometrial excitation-contraction coupling.

Decreased Ca2+ extrusion via Na+/Ca2+ exchange in epicardial left ventricular myocytes during compensated hypertrophy.

Hypertension-induced cardiac hypertrophy alters the amplitude and time course of the systolic Ca2+ transient of subepicardial and subendocardial ventricular myocytes. The present study was designed to elucidate the mechanisms underlying these changes. Myocytes were isolated from the left ventricular subepicardium and subendocardium of 20-wk-old spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY; control). We monitored intracellular Ca2+ using fluo 3 or fura 2; caffeine (20 mmol/l) was used to release Ca2+ from the sarcoplasmic reticulum (SR), and Ni2+ (10 mM) was used to inhibit Na+/Ca2+ exchange (NCX) function. SHR myocytes were significantly larger than those from WKY hearts, consistent with cellular hypertrophy. Subepicardial myocytes from SHR hearts showed larger Ca2+ transient amplitude and SR Ca2+ content and less Ca2+ extrusion via NCX compared with subepicardial WKY myocytes. These parameters did not change in subendocardial myocytes. The time course of decline of the Ca2+ transient was the same in all groups of cells, but its time to peak was shorter in subepicardial cells than in subendocardial cells in WKY and SHR and was slightly prolonged in subendocardial SHR cells compared with WKY subendocardial myocytes. It is concluded that the major change in Ca2+ cycling during compensated hypertrophy in SHR is a decrease in NCX activity in subepicardial cells; this increases SR Ca2+ content and hence Ca2+ transient amplitude, thus helping to maintain the strength of contraction in the face of an increased afterload.

Expression of heart K+ channels in adrenalectomized and catecholamine-depleted reserpine-treated rats.

We studied cardiac outward K currents (transient and sustained) by the whole-cell patch-clamp technique and the Kv4.2, Kv4.3, Kv1.4, Kv1.5, Kv1.2 and Kv2.1 expression of voltage-gated K channel by RT-PCR, in ventricular myocytes from two models of catecholamine-depleted adult rats. We induced endogenous catecholamine depletion by reserpine treatment and used adrenalectomized rats as a model of plasma catecholamine depletion. In reserpine-treated rats (97% decrease in endogenous norepinephrine content of the heart), the amplitude of the transient outward current was decreased by 48% and Kv4.2 and Kv4.3 mRNA levels were decreased by 57% and 34%, respectively. The amount of Kv1.5 mRNA tripled, with no change in sustained current density. This increase was not confirmed by immunostaining for the Kv1.5 protein. The amplitude of K currents and their corresponding mRNA levels returned to control values following recovery from reserpine treatment. In contrast, in adrenalectomized rats (98% decrease in plasma epinephrine concentration), we observed no change in the amplitude of outward K currents or in Kv mRNA levels. These results suggested a role for sympathetic innervation and endogenous norepinephrine in the regulation of transcription of cardiac outward K currents in physiological and pathological situations.

Depressed transient outward potassium current density in catecholamine-depleted rat ventricular myocytes.

The effect of catecholamine depletion (induced by prior treatment with reserpine) was studied in Wistar rat ventricular myocytes using whole cell voltage-clamp methods. Two calcium-independent outward currents, the transient outward potassium current (I(to)) and the sustained outward potassium current (I(sus)), were measured. Reserpine treatment decreased tissue norepinephrine content by 97%. Action potential duration in the isolated perfused heart was significantly increased in reserpine-treated hearts. In isolated ventricular myocytes, I(to) density was decreased by 49% in reserpine-treated rats. This treatment had no effect on I(sus). The I(to) steady-state inactivation-voltage relationship and recovery from inactivation remained unchanged, whereas the conductance-voltage activation curve for reserpine-treated rats was significantly shifted (6.7 mV) toward negative potentials. The incubation of myocytes with 10 microM norepinephrine for 7-10 h restored I(to), an effect that was abolished by the presence of actinomycin D. Norepinephrine (0.5 microM) had no effect on I(to). However, in the presence of both 0.5 microM norepinephrine and neuropeptide Y (0.1 microM), I(to) density was restored to its control value. These results suggest that the sympathetic nervous system is involved in I(to) regulation. Sympathetic norepinephrine depletion decreased the number of functional channels via an effect on the alpha-adrenergic cascade and norepinephrine is able to restore expression of I(to) channels.