Potassium Channel Blocker Research Articles

Isosmotic Striction of Rat Aorta Smooth Muscle Cells During Activation of Purinergic Receptors: Role of Chlorine Transport

We studied the effect of the purinergic signaling system and Cl-transporters on vascular smooth muscle cells (SMC) isosmotic striction that occurs when osmotic pressure is normalized after prolonged incubation in a hypoosmotic medium. The study was performed with the method of myography on endothelium-denuded ring segments of the male Wistar rats aorta. Isosmotic striction was induced by placing the vascular segments in normosmotic Krebs solution containing 120 mM NaCl after a 40-minute incubation in a hyposmotic Krebs solution containing 40 mM NaCl. Purinergic receptors were activated by adenosine 5'-triphosphate (ATP, 500 μM) as nonselective P2X and P2Y receptor agonist, and uridine 5'-triphosphate (UTP, 500 μM) as selective P2Y receptor agonist. ATP and UTP eliminated the transient nature of the aorta SMC isosmotic striction without affecting its amplitude. Pretreatment of vascular segments with ATP and UTP during incubation in a hyposmotic solution completely suppressed the development of isosmotic striction in the presence of ATP or UTP, but did not affect isosmotic striction without activators of purinergic receptors. The inhibitor of Na+, K+, 2Cl--cotransport (NKCC) bumetanide (100 μM) abolished isosmotic striction in the presence of ATP, but not UTP, but restored its transient character. A non-selective blocker of Cl– channels and Cl–, HCO3– exchanger DIDS (100 μM) suppressed the development of isosmotic striction both in the presence of ATP and UTP. The potassium channel blocker tetraethylammonium (10 mM) potentiates the constrictor action of UTP on isosmotic striction. We suppose purinergic receptors eliminate the transient isosmotic striction by activating Cl– currents through activation of P2Y receptors. The mechanism of interaction between the purinergic signaling system and Cl– transport during changes in cell volume requires further study.

12237 Monosynaptic Gabaergic Signaling From Suprachiasmatic Nucleus Neuromedin S Neurons To Preoptic Area Kisspeptin Neurons In Mice

Abstract Disclosure: W.I. Abdulmajeed: None. B.B. Jamieson: None. S.X. Thomas: None. Y. Rim: None. A.G. Novak: None. R.E. Campbell: None. R. Piet: None. In female rodents, projections from suprachiasmatic nucleus (SCN) neurons relay timing cues to the gonadotropin-releasing hormone (GnRH) neuronal network for the preovulatory surge. Kisspeptin (KISS1) neurons of the rostral periventricular area of the third ventricle (RP3V) are thought to integrate these cues with estradiol positive feedback to drive GnRH neuron activity, the gonadotropin surge and ovulation. We recently reported that SCN neuron projections release arginine vasopressin (AVP), thereby stimulating female RP3VKiss[1] neuron action potential firing in an estrous cycle stage-dependent manner. In the SCN, AVP is expressed in a subset of neuromedin S (NMS) neurons, a neuronal population essential for circadian rhythms. Moreover, a previous report indicates that exogenous NMS stimulates LH secretion in female rodents. SCNNMS neurons might, therefore, play a role in timing the preovulatory surge. However, whether SCNNMS neurons project to and regulate the activity of RP3VKISS[1] neurons is currently unknown. To address this question, we combined anterograde viral tract-tracing and channelrhodopsin-2 (ChR2)- assisted circuit mapping. Female mice expressing Cre recombinase in NMS cells (NMS-Cre) received stereotaxic injections in the SCN of adeno-associated viral vectors (AAVs) carrying the Cre-dependent sequence for mCherry. Fluorescence immunohistochemistry revealed that mCherry-expressing fibers come in close apposition with the great majority (>80%) of KISS1-immunoreactive neurons in the RP3V, suggesting a SCNNMS-to-RP3VKISS[1] neuron circuit. To interrogate this circuit, we next injected AAVs carrying Cre-dependent channelrhodopsin (ChR2) in the SCN of female NMS-Cre mice that also express the green fluorescent protein in KISS1 cells. Blue LED light (460-487 nm) activation of ChR2-expressing SCNNMS neuronal fibers in the RP3V evoked postsynaptic currents (PSCs) in most KISS1 neurons recorded in whole-cell voltage clamp (-60 mV) in brain slices. Evoked PSCs had short latencies and were blocked by bath application of 0.5 µM tetrodotoxin (TTX), indicating that they were generated by action potential-dependent release. Addition of 100 µM 4-Aminopyridine (4-AP, a potassium channel blocker) to TTX rescued these responses, indicating the existence of a monosynaptic SCNNMS-to-RP3VKISS[1] connection. In addition, evoked PSCs were suppressed by 5 µM gabazine, a GABAA receptor antagonist, but not by 20 µM NBQX and 50 µM D-AP5, AMPA- and NMDA-type glutamate receptor antagonists, respectively, revealing that SCNNMS projections release GABA onto RP3VKISS[1] neurons. Together, our findings are consistent with SCNNMS neurons extending monosynaptic GABAergic projections to RP3VKISS[1] neurons. Further studies are needed to determine the impact of these projections on RP3VKISS[1] neuron activity and the role they might play in the preovulatory surge. Presentation: 6/1/2024

Pharmacological evaluation of a new nanoformulation in the erectile tissue of rabbits and humans

The failure of achieving a penile erection for satisfactory sexual intercourse is known as erectile dysfunction (ED). The primary mediator for penile erection is nitric oxide (NO). ED is often associated with endothelial/nitrergic dysfunction characterized by a reduction of the bioavailability of NO. Phosphodiesterase-5 inhibitors (PDE-5Is) clinical efficacy in the treatment of ED depends on the integrity of the NO-sGC-PKG pathway. In the present study, we probed the effect of sodium nitroprusside incorporated into mesoporous silica nanoparticles (MPSi-NP), which traps cyanide and slowly releases NO. MPSi-NP induced a maximal relaxation of 92.8 ± 5.2% in rabbit corpora cavernosa (RbCC), blunted by a soluble guanylate cyclase (sGC) inhibitor and blockers of calcium-dependent potassium channels. MPSi-NP abolished spontaneous contractions of human corpora cavernosa (HCC) strips. In addition, MPSi-NP induced maximal relaxation of phenylephrine precontracted HCC by 118.6 ± 3.6%, and in comparison, tadalafil induced a maximal relaxation of HCC by 98.3 ± 1.2%. Similarly, the sGC inhibitor blocked the MPSi-NP relaxation. MPSi-NP potentiated the relaxation induced by tadalafil. MPSi-NP increased cGMP levels in HCC strips by 2.6-fold and increased by 3.5-fold the phosphorylation level of the VASP protein, which is a downstream target to PKG. MPSi-NP effectively relaxes RbCC and HCC by activating the sGC-PKG pathway and potentiates the tadalafil response. MPSi-NP could be helpful in conditions where nitric oxide availability is decreased. A topical gel formulation of MPSi-NP could be used as a rescue therapy to treat true non-responders of PDE5Is drugs.

In silico Discovery of Leptukalins, The New Potassium Channel Blockers from the Iranian Scorpion, Hemiscorpius Lepturus.

Blocking Kv 1.2 and Kv 1.3 potassium channels using scorpion venom- derived toxins holds potential therapeutic value. These channels are implicated in autoimmune diseases such as neurodegenerative diseases, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes. The present work aims at the discovery and in silico activity analysis of potassium channel blockers (KTxs) from the cDNA library derived from the venom gland of Iranian scorpion Hemiscorpius lepturus (H. lepturus). The sequence regarding potassium channel blockers were extracted based on Gene Ontology for H. lepturus venom gland. Homology analyses, superfamily, family, and evolutionary signatures of H. lepturus KTxs (H.L KTxs) were determined by using BLASTP, COBALT, PROSITE, and InterPro servers. The predicted 3D structures of H.L KTxs were superimposed against their homologs to predict structure activity relationship. Molecular docking analysis was also performed to predict the binding affinity of H.L KTxs to Kv 1.2 and Kv 1.3 channels. Finally, the toxicity was predicted. Seven H.L KTxs, designated as Leptukalin, were extracted from the cDNA library of H. lepturus venom gland. Homology analyses proved that they can act as potassium channel blockers and they belong to the superfamily and family of Scorpion Toxin-like and Short-chain scorpion toxins, respectively. Structural alignment results confirmed the activity of H.L KTxs. Binding affinity of all H.L KTxs to Kv 1.2 and Kv 1.3 channels ranged from -4.4 to -5.5 and -4 to -5.7 Kcal/mol, respectively. In silico toxicity assay showed that Leptukalin 3, Leptukalin 5, and Leptukalin 7 were non-toxic. Three non-toxic KTxs, Leptukalin 3, 5, and 7, were successfully discovered from the cDNA library of H. lepturus venom gland. Gathering all data together, the discovered peptides are promising potassium channel blockers. Accordingly, Leptukalin 3, 5, and 7 could be suggested for complementary in vitro studies and mouse model of autoimmune diseases.

Vasorelaxant Effect and Blood Pressure Reduction Potential of Pitaya Juice Concentrate (Stenocereus huastecorum) Associated with Calcium Channel Blockade.

Arterial hypertension is a highly prevalent chronic disease worldwide, with several etiologies and treatments that may eventually have side effects or result in patients developing tolerance. There is growing interest in traditional medicine and functional foods to isolate biomolecules that could be useful as coadjuvants for treating several aliments. Pitaya, a desert fruit endemic in Mexico, is a rich source of bioactive molecules (betalains and phenolic compounds). In this work, the vasorelaxation properties of pitaya juice concentrate and fraction one were investigated using aortic and mesenteric rings from rats. The incubation of rings with pitaya juice concentrate or fraction one induced significant vasorelaxation, independent of the endothelium, and showed resistance to potassium channel blockers. This vasorelaxation was associated with the transmembrane influx of extracellular calcium through the vascular smooth muscle cells, with an inhibitory effect on the voltage-dependent calcium channel currents. Also, 400 mg/mL of pitaya juice concentrate in spontaneous hypertensive rats reduced their blood pressure for 48 h. Phytochemical analyses showed that the primary compounds in F1 were glycosidic in nature, and could be a complex mixture of disaccharides, dimeric disaccharides, or even tetrasaccharides. The glycosidic compounds found in F1 primarily contributed to vasodilatation, establishing a voltage-dependent calcium channel inhibition as a possible molecular target.

Analysis of Molecular Mechanisms of Chronic Irradiation Effects on Electrical Signals in Wheat Plants

The effect of ionizing radiation (IR) on plants is mainly realized by altering the status of signaling systems and modifying stress signals. Variation potential (VP) is one of the types of electrical signals in plants. IR contributes to an increase in the amplitude of the VP, but the mechanisms of such influence are practically unknown. A possible way to implement changes arising from the action of IR is the regulation of gene expression. In the present work, the changes in the gene expression of participants in the generation and propagation of VP in irradiated plants are investigated. The experiments were performed on 14–15-day-old soft wheat plants (Triticum aestivum L.) grown under chronic irradiation (source 90Sr-90Y) with a dose rate of 31.3 μGy/h. The maximum accumulated dose was about 11.3 mGy. The irradiated plants showed no changes in the expression of calcium (TPC1), anionic (ALMT1 and CLC1), potassium (AKT1) channels, H+-ATPase (HA1), and NADPH oxidase (RBOHs) genes. A decrease in the expression of the SKOR potassium channel gene was revealed. The potassium channel blocker, tetraethylammonium chloride, caused an increase in response amplitude in control plants comparable to the increase in amplitude in the irradiated group. The obtained results indicate that one of the ways IR influences the electrical signals of plants is to inhibit the expression of the potassium channel.

Activity-dependent extracellular potassium changes in unmyelinated versus myelinated areas in olfactory regions of the isolated female guinea-pig brain

The potassium released in the extracellular space during neuronal activity is rapidly removed by glia and neurons to maintain tissue homeostasis. Oligodendrocyte-derived myelin axonal coating contributes to potassium buffering and is therefore crucial to control brain excitability.We studied activity-dependent extracellular potassium ([K+]o) changes in the piriform cortex (PC), a region that features highly segregated bundles of myelinated and unmyelinated fibers. Four-aminopyridine (4AP; 50 μM) treatment or patterned high-frequency stimulations (hfST) were utilized to generate [K+]o changes measured with potassium-sensitive electrodes in the myelinated lateral olfactory tract (LOT), in the unmyelinated PC layer I and in the myelinated deep PC layers in the ex vivo isolated guinea-pig brain.Seizure-like events induced by 4AP are initiated by the abrupt [K+]o rise in the layer I formed by unmyelinated fibers (Uva et al., 2017). Larger [K+]o shifts occurred in unmyelinated layers compared to the myelinated LOT. LOT hfST that mimicks pre-seizure discharges also generated higher [K+]o changes in unmyelinated PC layer I than in LOT and deep PC layers. The treatment with the Kir4.1 potassium channel blocker BaCl2 (100 μM) enhanced the [K+]o changes generated by hfST in myelinated structures.Our data show that activity-dependent [K+]o changes are intrinsically different in myelinated vs unmyelinated cortical regions. The larger [K+]o shifts generated in unmyelinated structures may represent a vehicle for seizure generation.

New Perspectives in The Management of Paroxysmal Atrial Fibrillation: Dual AntiArrhythmic Medications.

Atrial fibrillation (AF) is the most common cardiac arrhythmia encountered in clinical practice projected to affect 12.1 million individuals by the year 2030. Patients who are diagnosed with AF have an increased risk of morbidity and mortality. Although catheter ablation is a class I treatment recommendation in patients with symptomatic paroxysmal AF, antiarrhythmic medications (AAM) continue to be the mainstay of treatment in limited resource settings not offering ablation procedures. Currently, the most used AAMs are those which block either the sodium or potassium channels. We hypothesized that the use of selective dual AAM (sodium and potassium channel blockers) (DAAM) improves the chance of maintaining sinus rhythm and decreases the need for catheter ablation when compared with single AAM (SAAM). This retrospective observational study was conducted in 150 patients with paroxysmal AF over 5 years at Richmond University Medical Center in Staten Island, New York. The following data were collected: age, sex, comorbidities, electrocardiogram findings, ejection fraction by echocardiography, classes of AAM, duration, and response to treatments. The primary endpoint included the absence of symptoms and maintenance of sinus rhythm. The secondary endpoint included the requirement of electrical cardioversion or catheter ablation. A total of 86 patients met the inclusion criteria in our analysis. The average age of the patients was 71.06 years (SD = 7.66). About 45 patients were given DAAM of either amiodarone + flecainide or dronedarone + flecainide and were treated for an average of 15.4 months, followed by catheter ablation, if needed. Also, 41 patients received a SAAM followed by catheter ablation, if needed. A Mann-Whitney test indicated that electrical cardioversion and catheter ablation were greater for the SAAM group (Md = 1) than for the DAAM group (Md = 0) (U = 294.00, P value <0.001; U = 507.00, P value <0.001, respectively). No pro-arrhythmic side effects or death were encountered in either group. Treatment of paroxysmal AF with DAAM is effective compared with SAAM and is less likely to need catheter ablation or electrical cardioversion. Well-designed prospective studies are needed to further explore the use of DAAM in the management of paroxysmal AF and its clinical impact in limited resource settings.

Prevention and treatment of noise-induced hearing loss and cochlear synapse degeneration by potassium channel blockers in vivo.

Noise is a common deafness factor affecting more 100 million people in the United States. So far, there is no pharmacological treatment available. We show here that administration of K + channel blockers after noise exposure could attenuate noise-induced hearing loss and synapse degeneration, and improved behavioral responses. This is the first time to real the K + channel blockers that could treat noise-induced hearing loss and cochlear synaptopathy after noise exposure.

Chemical and biophysical characterization of novel potassium channel blocker 3-fluoro-5-methylpyridin-4-amine

4-aminopyridine (4AP) is a potassium (K+) channel blocker used clinically to improve walking in people with multiple sclerosis (MS). 4AP binds to exposed K+ channels in demyelinated axons, reducing the leakage of intracellular K+ and enhancing impulse conduction. Multiple derivatives of 4AP capable of blocking K+ channels have been reported including three radiolabeled with positron emitting isotopes for imaging demyelinated lesions using positron emission tomography (PET). However, there remains a demand for novel molecules with suitable physicochemical properties and binding affinity that can potentially be radiolabeled and used as PET radiotracers. In this study, we introduce 3-fluoro-5-methylpyridin-4-amine (5Me3F4AP) as a novel trisubstituted K+ channel blocker with potential application in PET. 5Me3F4AP has comparable potency to 4AP and the PET tracer 3-fluoro-4-aminopyridine (3F4AP). Compared to 3F4AP, 5Me3F4AP exhibits comparable basicity (pKa = 7.46 ± 0.01 vs. 7.37 ± 0.07, P-value = 0.08), greater lipophilicity (logD = 0.664 ± 0.005 vs. 0.414 ± 0.002, P-value < 0.0001) and higher permeability to an artificial brain membrane (Pe = 88.1 ± 18.3 vs. 31.1 ± 2.9 nm/s, P-value = 0.03). 5Me3F4AP is also more stable towards oxidation in vitro by the cytochrome P450 enzyme CYP2E1 (IC50 = 36.2 ± 2.5 vs. 15.4 ± 5.1, P-value = 0.0003); the enzyme responsible for the metabolism of 4AP and 3F4AP. Taken together, 5Me3F4AP has promising properties as a candidate for PET imaging warranting additional investigation.

Synthetic ShK-like Peptide from the Jellyfish Nemopilema nomurai Has Human Voltage-Gated Potassium-Channel-Blocking Activity.

We identified a new human voltage-gated potassium channel blocker, NnK-1, in the jellyfish Nemopilema nomurai based on its genomic information. The gene sequence encoding NnK-1 contains 5408 base pairs, with five introns and six exons. The coding sequence of the NnK-1 precursor is 894 nucleotides long and encodes 297 amino acids containing five presumptive ShK-like peptides. An electrophysiological assay demonstrated that the fifth peptide, NnK-1, which was chemically synthesized, is an effective blocker of hKv1.3, hKv1.4, and hKv1.5. Multiple-sequence alignment with cnidarian Shk-like peptides, which have Kv1.3-blocking activity, revealed that three residues (3Asp, 25Lys, and 34Thr) of NnK-1, together with six cysteine residues, were conserved. Therefore, we hypothesized that these three residues are crucial for the binding of the toxin to voltage-gated potassium channels. This notion was confirmed by an electrophysiological assay with a synthetic peptide (NnK-1 mu) where these three peptides were substituted with 3Glu, 25Arg, and 34Met. In conclusion, we successfully identified and characterized a new voltage-gated potassium channel blocker in jellyfish that interacts with three different voltage-gated potassium channels. A peptide that interacts with multiple voltage-gated potassium channels has many therapeutic applications in various physiological and pathophysiological contexts.

The relaxation effect of endocannabinoid anandamide on isolated rat bladder and vas deferens tissues and possible mechanisms.

The endocannabinoid system plays important roles in various systems, including the genitourinary system; however, its mechanism of action is not fully understood. This study aimed to investigate the direct relaxant effects of anandamide and its possible mechanisms in isolated rat bladder and vas deferens tissues. Twenty-one adult male Wistar albino rats were used. Bladder and vas deferens (prostatic and epididymal portions) tissues were mounted in 10 mL of organ baths. Relaxation responses to anandamide were recorded at 3 and 10 μM concentrations. After the rest period, the procedures were repeated in the presence of cannabinoid (CB) and vanilloid receptor antagonists, various potassium channel blockers, cyclo-oxygenase, and nitric oxide synthase inhibitors. In different tissues to investigate the Ca2+-channel antagonistic effect of anandamide, concentration-response curves to CaCl2 were obtained in the absence and presence of anandamide. Anandamide caused a significant relaxation response in the bladder and epididymal vas deferens tissues, but not in the prostatic portion. The effect of anandamide was antagonized in the presence of the CB1 antagonist AM251 or the non-selective potassium channel blocker tetraethylammonium in bladder tissue. In the epididymal vas deferens, anandamide significantly inhibited the calcium contraction responses, especially at high concentrations. The CB2 antagonist AM630 reversed this inhibition. The results show that anandamide has a direct relaxant effect on the isolated rat bladder and epididymal vas deferens. Anandamide triggers different mechanisms in different types of tissues, and further studies are needed to elucidate the mechanism of action of anandamide.

Purinergic inhibitory regulation of esophageal smooth muscle is mediated by P2Y receptors and ATP-dependent potassium channels in rats

Purines such as ATP are regulatory transmitters in motility of the gastrointestinal tract. The aims of this study were to propose functional roles of purinergic regulation of esophageal motility. An isolated segment of the rat esophagus was placed in an organ bath, and mechanical responses were recorded using a force transducer. Exogenous application of ATP (10–100 μM) evoked relaxation of the esophageal smooth muscle in a longitudinal direction under the condition of carbachol (1 μM) -induced precontraction. Pretreatment with a non-selective P2 receptor antagonist, suramin (500 μM), and a P2Y receptor antagonist, cibacron blue F3GA (200 μM), inhibited the ATP (100 μM) -induced relaxation, but a P2X receptor antagonist, pyridoxal phosphate-6-azophenyl-2,4-disulfonic acid (50 μM), did not affect it. A blocker of ATP-dependent potassium channels (KATP channels), glibenclamide (200 μM), inhibited the ATP-induced relaxation and application of an opener of KATP channels, nicorandil (50 μM), produced relaxation. The findings suggest that ATP is involved in inhibitory regulation of the longitudinal smooth muscle in the muscularis mucosae of the rat esophagus via activation of P2Y receptors and then opening of KATP channels.

Use of tetraethylammonium (TEA) and Tris loading for blocking TRPM7 channels in intact cells.

Tetraethylammonium (TEA), a quaternary ammonium compound, is a well-known blocker of potassium channels belonging to various subfamilies, such as KV1-3, KCa1, 2 and prokaryotic KcsA. In many cases, TEA acts from the extracellular side by open pore blockade. TEA can also block transient receptor potential (TRP) cation channels, such as TRPM7, in a voltage-dependent manner. In human T lymphocytes, intracellular (cytosolic) TEA and its analog TMA (tetramethylammonium) inhibit TRPM7 channel currents in the outward but not inward direction. By contrast, intracellular Mg2+, protons and polyamines inhibit both outward and inward current components equally. Likewise, the majority of available pharmacological tools inhibit TRPM7 channels in a voltage-independent manner. Since TRPM7 is a steeply outwardly rectifying conductance, voltage-dependent blockers can be useful for studying the cellular functions of this channel. TRPM7 protein is endogenously expressed in diverse cell lines, including HEK, HeLa, CHO, RBL and Jurkat. Using patch-clamp electrophysiology, we found that incubating HEK293 and Jurkat T cells overnight in the presence of 20mM TEA-Cl, resulted in the nearly complete blockade of whole-cell TRPM7 outward current, measured at break-in. By contrast, the inward current was unchanged in TEA-loaded cells. The blockade was fully reversible after washout of intracellular solution in whole-cell but not in perforated-patch recording configurations. Overnight incubation with 20mM TMA-Cl resulted in a more modest blockade of the outward TRPM7 current. Internal 129mM TMA and TEA eliminated most of the outward current. TEA uptake in transfected HEK293 cells led to blockade of recombinant murine TRPM7 and the Mg2+ and pH insensitive Ser1107Arg variant. Unexpectedly, Tris-HCl, a widely used pH buffer, could similarly be loaded into Jurkat and HEK cells, and preferentially blocked outward TRPM7 currents. 20mM and 129mM Tris in the internal solution blocked TRPM7 current in outward but not inward direction. Voltage-dependent channel blockade by TEA, TMA and Tris loading will be useful for studying the properties and functions of TRPM7-mediated ion transport in intact cells.

Effects of plant extracts and derivatives on cardiac K+, Nav, and Cav channels: a review.

Natural products (NPs) are endless sources of compounds for fighting against several pathologies. Many dysfunctions, including cardiovascular disorders, such as cardiac arrhythmias have their modes of action regulation of the concentration of electrolytes inside and outside the cell targeting ion channels. Here, we highlight plant extracts and secondary metabolites' effects on the treatment of related cardiac pathologies on hERG, Nav, and Cav of cardiomyocytes. The natural product's pharmacology of expressed receptors like alpha-adrenergic receptors causes an influx of Ca2+ ions through receptor-operated Ca2+ ion channels. We also examine the NPs associated with cardiac contractions such as myocardial contractility by reducing the L-type calcium current and decreasing the intracellular calcium transient, inhibiting the K+ induced contractions, decreasing amplitude of myocyte shortening and showed negative ionotropic and chronotropic effects due to decreasing cytosolic Ca2+. We examine whether the NPs block potassium channels, particular the hERG channel and regulatory effects on Nav1.7.

Intracellular pathways of calcitonin gene-related peptide-induced relaxation of human coronary arteries: A key role for Gβγ subunit instead of cAMP.

Calcitonin gene-related peptide (CGRP) is a potent vasodilator. While its signalling is assumed to be mediated via increases in cAMP, this study focused on elucidating the actual intracellular signalling pathways involved in CGRP-induced relaxation of human isolated coronary arteries (HCA). HCA were obtained from heart valve donors (27 M, 25 F, age 54 ±2years). Concentration-response curves to human α-CGRP or forskolin were constructed in HCA segments, incubated with different inhibitors of intracellular signalling pathways, and intracellular cAMP levels were measured with and without stimulation. Adenylyl cyclase (AC) inhibitors SQ22536 + DDA and MDL-12330A, and PKA inhibitors Rp-8-Br-cAMPs and H89, did not inhibit CGRP-induced relaxation of HCA, nor did the guanylyl cyclase inhibitor ODQ, PKG inhibitor KT5823, EPAC1/2 inhibitor ESI09, potassium channel blockers TRAM-34 + apamin, iberiotoxin or glibenclamide, or the Gαq inhibitor YM-254890. Phosphodiesterase inhibitors induced a concentration-dependent decrease in the response to KCl but did not potentiate relaxation to CGRP. Relaxation to forskolin was not blocked by PKA or AC inhibitors, although AC inhibitors significantly inhibited the increase in cAMP. Inhibition of Gβγ subunits using gallein significantly inhibited the relaxation to CGRP in human coronary arteries. While CGRP signalling is generally assumed to act via cAMP, the CGRP-induced vasodilation in HCA was not inhibited by targeting this intracellular signalling pathway at different levels. Instead, inhibition of Gβγ subunits did inhibit the relaxation to CGRP, suggesting a different mechanism of CGRP-induced relaxation than generally believed.

Efficacy and Safety of Intravenous Vernakalant in Rapid Cardioversion of Recent Onset Atrial Fibrillation: A Retrospective Single-Centre Study.

We use vernakalant, an intravenous anti-arrhythmic, to cardiovert paroxysmal atrial fibrillation (AF) into sinus rhythm. It is a relatively atrium-selective, early-activating potassium and frequency-dependent sodium channel blocker with a half-life of 2 to 3 hours. Due to concerns regarding its safety profile, it is not Food and Drug Administration (FDA)-approved. This study aims to assess the efficacy of intravenous vernakalant in cardioversion of paroxysmal AF and the safety of its use. Patients with paroxysmal AF who presented to the American University of Beirut Medical Center (AUBMC) between 2015 and 2020 and received vernakalant for cardioversion were included. Patients did not receive vernakalant if they had any of the following: QTc > 440 ms, heart rate < 50 bpm, acute coronary syndrome within the last 30 days, second- and third-degree atrioventricular (AV) block in the absence of a pacemaker, severe aortic stenosis (AS), use of intravenous antiarrhythmics (class I and class III) within four hours of vernakalant infusion, systolic blood pressure <100 mmHg, and heart failure (New York Heart Association (NYHA) III or NYHA IV class). The primary endpoint is conversion to sinus rhythm for at least one minute within 90 minutes of the start of the vernakalant infusion. The secondary endpoint included the presence of these side effects: bradycardia, QTc prolongation, AV block, ventricular arrhythmias, hypotension, taste alteration/dysgeusia, sneezing, nausea, vomiting, paresthesia, cardiogenic shock, or death. The study included 23 patients with paroxysmal AF (15 men, mean age 54 ± 14 years). Fourteen patients (61%) cardioverted to sinus rhythm within 90 minutes of the start of the Vernakalant infusion. Seven patients (30%) reverted to sinus rhythm within 15 minutes after the first infusion. After treatment with vernakalant, four patients (17%) developed sinus bradycardia, and four patients (17%) developed first-degree AV block. No patient had a QTc greater than 460 ms. None of the patients experienced sinus pauses, high-grade AV block, ventricular arrhythmias, hypotension, dysgeusia, sneezing, nausea, vomiting, paresthesia, cardiogenic shock, or death. Vernakalant had 61% efficacy in the rapid cardioversion of paroxysmal AF to sinus rhythm, was well tolerated, and had a low rate of adverse events in our study population.

Exploring the therapeutic potential of pomegranate juice for uterine relaxation

ABSTRACT Background The effects of pomegranate juice (PJ) and its components on uterine smooth muscle are unknown. Hence, this study unequivocally demonstrates that pomegranate juice (PJ) significantly impacts myometrial function, providing crucial insights into its relaxant properties and their potential therapeutic applications for uterine-related disorders. Research design and methods Rat uterine smooth muscle horn strips were suspended in Krebs solution organ baths. Contractions were measured isometrically using a transducer (AD instrument Australia). The effects of PJ were evaluated on contractile activity elicited by potassium chloride (KCl 60 Mm) depolarization. Inhibitors of nitric oxide (L-NAME 3 X 10−4), guanylate cyclase (methylene blue 1 X 10−5), and Prostaglandin I2 (indomethacin 3 X 10−5), as well as Potassium Channels blockers, were determined. Results The juice at concentrations from 1.5–5 mg/ml significantly decreased the rat uterine horn contraction induced by KCl. The NO, cGMP, and PGI2 inhibitors did not block the relaxation response. Furthermore, the PGI2 inhibitor significantly enhanced the relaxation effects; K+ channel blockers had no inhibitory effects on the relaxation responses. Contrarily, GLIB improved considerably relaxation. Conclusion Research suggests pomegranate juice’s active ingredient may reduce uterine contractions and treat uterotonic disorders, potentially preventing preterm birth and dysmenorrhea. Further research is needed to determine its mechanism of action. Trial registration Code: AEC-013

4-aminopyridine improves evoked potentials and ambulation in the taiep rat: A model of hypomyelination with atrophy of basal ganglia and cerebellum.

The taiep rat is a tubulin mutant with an early hypomyelination followed by progressive demyelination of the central nervous system due to a point mutation in the Tubb4a gene. It shows clinical, radiological, and pathological signs like those of the human leukodystrophy hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Taiep rats had tremor, ataxia, immobility episodes, epilepsy, and paralysis; the acronym of these signs given the name to this autosomal recessive trait. The aim of this study was to analyze the characteristics of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) in adult taiep rats and in a patient suffering from H-ABC. Additionally, we evaluated the effects of 4-aminopyridine (4-AP) on sensory responses and locomotion and finally, we compared myelin loss in the spinal cord of adult taiep and wild type (WT) rats using immunostaining. Our results showed delayed SSEPs in the upper and the absence of them in the lower extremities in a human patient. In taiep rats SSEPs had a delayed second negative evoked responses and were more susceptible to delayed responses with iterative stimulation with respect to WT. MEPs were produced by bipolar stimulation of the primary motor cortex generating a direct wave in WT rats followed by several indirect waves, but taiep rats had fused MEPs. Importantly, taiep SSEPs improved after systemic administration of 4-AP, a potassium channel blocker, and this drug induced an increase in the horizontal displacement measured in a novelty-induced locomotor test. In taiep subjects have a significant decrease in the immunostaining of myelin in the anterior and ventral funiculi of the lumbar spinal cord with respect to WT rats. In conclusion, evoked potentials are useful to evaluate myelin alterations in a leukodystrophy, which improved after systemic administration of 4-AP. Our results have a translational value because our findings have implications in future medical trials for H-ABC patients or with other leukodystrophies.

The Roles of Potassium Channels and Nitric oxide in the Modulation of Apelin induced-relaxation in Isolated Diabetic Rat Aorta

Diabetes is associated with endothelial dysfunction, which impairs blood vesselscapacity to maintain vascular tone. Apelin is an adipocyte-produced relaxing factor that has endothelium-dependent and nitric oxide (NO)-mediated vasorelaxant effects. The current study investigated how streptozotocin (STZ)-induced type one diabetes modulates the mechanisms involved in aortic vascular response to apelin, focusing on the role of potassium channels and endothelial derived relaxing factors (EDRF). In this study, precontracted rat thoracic aortic segments were pre-incubated with the NO inhibitor, cyclooxygenase (COX) inhibitor and potassium channels blockers including: non-selective calcium-activated potassium channel, big conductance calcium-activated potassium channels (BKca), intermediate conductance calcium activated potassium channels (IKca), delayed inward rectifier potassium channels (Kir), adenosine triphosphates-sensitive potassium channels (KATP) and voltage sensitive potassium channels (Kv) blockers, then cumulative concentrations of apelin were applied to each group in both non-diabetic and diabetic conditions. The statistical analysis between diabetic and non-diabetic groups revealed that endothelial impairment induced by diabetes in rat thoracic aorta remarkably attenuated the vascular responses to apelin. An important new finding in this study was that almost all potassium channels blockers noticeably P&lt;0.001 increased apelin efficacy with relatively no changes in the peptide potency. However, in diabetic aortic segments, the non-selective Kca, BKca blockers, NO inhibitor and COX inhibitor reversed vascular responses to apelin, but Kir, KATP and Kv blockers significantly reduced vascular responses to apelin in comparison to control rats. It is worth noting that diabetes did not only alter the peptide potency in these experimental groups but also significantly increased the maximum responses when Kca and BKca blockers preincubated. In conclusion, our findings shed light on the mechanisms behind diabetes-induced aortic artery hypo-reactivity to apelin which involve the inhibition of endothelial NO synthase activities and decreased contribution of Kca, BKca, IKca, Kv, Kir and KATP channels.