Rectifier Potassium Research Articles

Inhibitory G-protein-mediated modulation of slow delayed rectifier potassium channels contributes to increased susceptibility to arrhythmogenesis in aging heart.

Slow delayed rectifier potassium current (IKs) is an important component of repolarization reserve during sympathetic nerve excitement. However, little is known about age-related functional changes of IKs and its involvement in age-dependent arrhythmogenesis. The purpose of this study was to investigate age-related alteration of the IKs response to β-adrenergic receptor (βAR) activation. Dunkin-Hartley guinea pigs were used. Whole-cell patch-clamp recording was used to record K+ currents. Optical mapping of membrane potential was performed in exvivo heart. There was no difference in IKs density in ventricular cardiomyocytes between young and old guinea pigs. However, in contrast to IKs potentiation in young hearts, isoproterenol (ISO) evoked an acute inhibition on IKs in a concentration-dependent manner in old guinea pig hearts. The β2AR antagonist, but not β1AR antagonist, reversed the inhibitory response. Preincubation of cardiomyocytes with the inhibitory G protein (Gi) inhibitor pertussis toxin (PTX) also reversed the inhibitory response. In HEK293 cells cotransfected with cloned IKs channel and β2AR, ISO enhanced the current but reduced it when cells were cotransfected with Gi2, and PTX restored the ISO-induced excitatory response. Moreover, in aging cardiomyocytes, Gβγ inhibitor gallein, PLC inhibitor U73122, or protein kinase C inhibitor Bis-1 prevented the reduction of IKs by ISO. Furthermore, cardiac-specific Gi2 overexpression in young guinea pigs predisposed the heart to ventricular tachyarrhythmias. PTX pretreatment protected the hearts from ventricular arrhythmias. βAR activation acutely induces an inhibitory IKs response in aging guinea pig hearts through β2AR-Gi signaling, which contributes to increased susceptibility to arrhythmogenesis in aging hearts.

The Agonist of Inward Rectifier Potassium Channel (IK1) Attenuates Rat Reperfusion Arrhythmias Linked to CaMKII Signaling.

Inward rectifier potassium channels (IK1, Kir) are known to play critical roles in arrhythmogenesis. Thus, how IK1 agonist affects reperfusion arrhythmias needs to be clarified, and its underlying mechanisms should be determined. Reperfusion arrhythmias were modeled by coronary ligation (ischemia, 15 minutes) and release (reperfusion, 15 minutes). Zacopride (1.5-50 μg/kg in vivo, or 0.1-10 μmol/Lex vivo) was applied in the settings of pretreatment (3 minutes before coronary ligation) and posttreatment (5 minutes after coronary ligation). Hypoxia (45 minutes) /reoxygenation (30 minutes) model was established in cultured H9c2 (2-1) cardiomyocytes. Zacopride or KN93 was applied before hypoxia (pretreatment). In the setting of pre- or posttreatment, zacopride at 15 μg/kg in vivo or 1 μmol/Lin vitro exhibited superlative protections on reperfusion arrhythmias or intracellular calcium overload. Western blot data from ex vivo hearts or H9c2 (2-1) cardiomyocytes showed that I/R (H/R) induced the inhibition of Kir2.1 (the dominant subunit of IK1 channel in ventricle), phosphorylation and oxidation of CaMKII, downregulation of SERCA2, phosphorylation of phospholamban (at Thr17), and activation of caspase-3. Zacopride treatment (1 μmol/L) was noted to strikingly restore the expression of Kir2.1 and SERCA2 and decrease the activity of CaMKII, phospholamban, and caspase-3. These effects were largely eliminated by co-application of IK1 blocker BaCl2. CaMKII inhibitor KN93 attenuated calcium overload and p-PLB (Thr17) in an IK1-independent manner. IK1-depedent inhibition of CaMKII activity is found to be a key cardiac salvage signaling under Ca2+ dyshomeostasis and reactive oxygen species (ROS) stress. IK1 might be a novel target for pharmacological conditioning of reperfusion arrhythmia, especially for the application after unpredictable ischemia.

Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling.

Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Cavα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (INa), transient outward potassium current (Ito), L-type calcium channel peak current (ICa,L), rapid and slow components of the delayed rectifier potassium current (IKr and IKs), and inward rectifier (IK1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.

Abstract 13939: Triiodothyronine and Dexamethasone Enhances Electrophysiological Maturation of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Background: Human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) technology opens new avenues for disease modeling and drug development. However, hiPSC-CMs remain functionally immature, which hinders their utility as a model of human cardiomyocytes. Objective: To improve the electrophysiological maturation of hiPSC-CMs. Methods and Results: Day 16 th hiPSC-CMs were treated with vehicle or 100 nmol/L triiodothyronine (T3) and 1 μmol/L Dexamethasone (Dex) for 14 days. On day 30 th , hiPSC-CMs were dissociated and replated as cell sheets or single cells. Optical mapping and patch-clamp technique were used to examine the electrophysiological properties of vehicle- and T3+Dex-treated hiPSC-CMs. T3+Dex-treated hiPSC-CMs had a slower spontaneous beating rate (vehicle 17 ± 0.8 vs . T3+Dex 12 ± 0.8 beats/min, P < 0.01), more hyperpolarized resting membrane potential (vehicle -65.04 ± 1.20 vs. T3+Dex -72.00 ± 1.10 mV, P < 0.01), faster maximal upstroke velocity (vehicle 86.08 ± 8.12 vs. T3+Dex 131.78 ± 8.49 mV/ms, P < 0.01), and shorter action potential duration at 90% repolarization (APD 90 , vehicle 550.44 ± 39.54 vs. T3+Dex 418.59 ± 21.58 ms, P < 0.01) compared to the vehicle. Changes in spontaneous activity and AP were mediated by decreasing the funny current (I f , vehicle -12.20 ± 2.15 vs. T3+Dex -6.98 ± 0.89 pA/pF at -120 mV, P < 0.05) and increasing the inward rectifier potassium current (I K1 , vehicle -4.62 ± 0.59 pA/pF vs . T3+Dex -18.79 ± 1.98 pA/pF at -120 mV, P < 0.01), the sodium current (I Na , vehicle -9.8 ± 1.86 vs. T3+Dex -44.9 ± 7.10 pA/pF at -30 mV, P < 0.01), and the rapidly and slowly activating delayed rectifier potassium currents (I Kr , 0.81 ± 0.07 vs. T3+Dex: 1.35 ± 0.19 pA/pF at 20 mV, P < 0.01; I Ks , vehicle 0.38 ± 0.06 vs. T3+Dex 0.72 ± 0.17 pA/pF at 40 mV, P < 0.05). Furthermore, T3+Dex-treated hiPSC-CM cell sheets (hiPSC-CCSs) exhibited a faster conduction velocity and shorter APD than the vehicle. Inhibition of I K1 by 100 μM BaCl 2 significantly slowed conduction velocity and prolonged APD in T3+Dex-treated hiPSC-CCSs but had no effect in the vehicle group, demonstrating the important role of I K1 for conduction velocity and APD. Conclusion: T3+Dex treatment is an effective approach to rapidly enhance electrophysiological maturation of hiPSC-CMs.

Abstract 14241: Cigarette Smoke Causes Atrial Fibrillation via PiP2 Signaling

Introduction: Cigarette smoking (CS) is a major cause of cardiovascular diseases. Smokers are at a significantly higher risk for developing atrial fibrillation (AF), a dangerous and abnormal heart rhythm. In the US, 15.5% of adults are current smokers, and it is becoming clear that CS is an independent risk factor for AF, but a detailed mechanistic understanding of how CS contributes to the molecular patho-electrophysiology of AF remains elusive. We investigated if CS related AF is in part mediated through a mechanism that depends on the cardiac acetylcholine activated inward rectifier potassium current (I KACh ). Hypothesis: We tested the hypothesis that CS stimulates phosphatidylinositol 4-phosphate 5-kinase alpha (PIP5K) signaling, leading to increased cellular phosphatidylinositol 4,5- bisphosphate (PiP2) levels, and subsequent I KACh activation and AF perpetuation. Methods: We used patch clamp in HEK293 cells expressing Kir3.1 and Kir3.4, the molecular correlates of IKACh, cultured in the presence of 5% CS extracts. In vivo inducibility of AF was assessed in mice exposed to CS for 8 weeks. Results: In HEK293 cells, 24 h incubation with CSE increased the cellular PiP2 levels, and increased I KACh . Addition of 5 uM ISA, an inhibitor of PIP5K, abrogated the CS effects on I KACh, indicating that CS activates PIP5K. Finally, intrajugular injection of tertiapinQ, an I KACh blocker, terminated atrial fibrillation in mice exposed to CS for 8 weeks. Conclusions: Cigarette smoke modifies the atrial electrophysiological substrate, leading to arrhythmogenesis, in part, through I KACh activation by increasing the cellular levels of PiP2.

Hyperemesis Gravidarum Presenting as Severe Hypokalemic Periodic Paralysis and Type II Respiratory Failure: A Different Form of Thyroid Storm?

Hyperthyroidism in pregnancy is a condition that results from an excess of beta-human chorionic gonadotropin hormone resulting in gestational thyrotoxicosis. This thyrotoxicosis of pregnancy might be linked with hyperemesis gravidarum and is usually a self-limiting disease. Hyperthyroidism can cause hypokalemic periodic paralysis, which presents as pure motor areflexic flaccid paralysis. In severe cases, it may involve respiratory muscles and cause hypercapnic respiratory failure requiring invasive ventilation. A positive feed-forward cycle of hypokalemia could be triggered by the loss of function of inward rectifier potassium channel 18 (Kir2.6) along with the increased activity of sodium, potassium-adenosine triphosphatase (Na⁺/K⁺-ATPase). Hyperthyroid periodic paralysis is characterized by biochemical hyperthyroidism, normal urine potassium excretion, and electrocardiography abnormalities.We report a case of a 23-year-old female (G2P0L0A1) who had severe hyperemesis gravidarum and later on developed flaccid quadriplegia. Her thyroid profile revealed hyperthyroidism. She later developed hypercapnic respiratory failure and was managed by potassium replacement and invasive ventilation.

Baicalin suppresses neuron autophagy and apoptosis by regulating astrocyte polarization in pentylenetetrazol-induced epileptic rats and PC12 cells

Epilepsy is a common chronic neurological disorder worldwide, but its entire pathology remains unknown. The purpose of this study was to explore the antiepileptic effect of baicalin (BAL), the main bioactive component of scutellaria. We isolated astrocytes from neonatal rats and astrocytes were identified by glial fibrillary acidic protein (GFAP) immunostaining. The viability and phenotype of astrocytes were determined by Cell Counting Kit-8 (CCK-8) and immunofluorescence staining, respectively. For investigating the effect of BAL on the autophagy in A1 astrocytes treated PC12 cells, expression of light chain 3B (LC3-B) and sequestosome 1 (P62) was analyzed by immunofluorescence staining and apoptosis by acridine orange/ethidium bromide (AO/EB) staining, respectively. For animal experiments, pentylenetetrazol (PTZ)-induced epileptic model was used to explore the antiepileptic effect of BAL. The results showed that BAL reduced lipopolysaccharide (LPS)-induced complement C3 (C3, a marker of A1 astrocytes) + A1 cells and decreased autophagy and apoptosis in PC12 cells. Further findings showed seizure grade and latency were positively correlated with GFAP+/C3 + A1 cells’ infiltration in interstitial astrocytes. After BAL treatment, epileptogenesis was ameliorated with decreased A1 astrocytes in the brain and improved behavioral performance. The enzyme-linked immunosorbent assay (ELISA) showed that the levels of interleukin-1α (IL-1α) and tumor necrosis factor-α (TNF-α) were reduced in the cerebral interstitial site in the BAL group compared to the PTZ group. Western blotting analysis showed that BAL treatment reduced expression of C3, inward rectifier potassium channel Kir4.1, aquaporin-4 (AQP4) in the frontal cortex and Caspase-3, BCL2-associated X protein (Bax) in the hippocampus. In conclusion, these findings suggest that BAL can prevents cognitive and emotional disorders and has antiepileptic effects in rats, which may be associated with suppresses neuron autophagy and apoptosis in the hippocampus via regulate astrocyte phenotypes.

Novel Serum Biomarkers of Neurovascular Unit Associated with Cortical Amyloid Deposition.

Whether blood biomarkers of neurovascular unit are associated with cortical amyloid deposition on positron emission tomography (PET) imaging remains unclear. To investigate the association between novel serum biomarkers of neurovascular unit, such as protein tyrosine phosphatase receptor type B (PTPRB), gap junction protein alpha-5 (GJA5), adenosine triphosphate-sensitive inward rectifier potassium channel-8 (KCNJ8), and von Willebrand factor (vWF), and cortical amyloid deposition. Between 2012 and 2018, 68 elderly individuals with amnestic mild cognitive impairment (32 men and 36 women; mean age 75.2 years) were enrolled. All participants underwent 11C-Pittsburgh compound-B (PiB)-PET, 18F-fluorodeoxyglucose-PET, and measurement of serum PTPRB, GJA5, KCNJ8, and vWF levels using commercially available human enzyme-linked immunosorbent assay kits. Based on the mean cortical standardized uptake value ratio, the participants were divided into two groups: PiB-negative group and PiB-positive group. Serum levels of PTPRB, GJA5, KCNJ8, and vWF were compared between the two groups. Multiple linear regression analysis was performed to investigate the relationship between serum PTPRB, GJA5, KCNJ8, and vWF levels and cortical amyloid deposition. PTPRB and GJA5 levels were significantly lower and KCNJ8 and vWF levels were significantly higher in the PiB-positive group than in the PiB-negative group. PTPRB and GJA5 levels inversely correlated with mean PiB uptake, whereas KCNJ8 and vWF levels positively correlated with mean PiB uptake. Serum levels of PTPRB, GJA5, KCNJ8, and vWF correlate with cortical amyloid deposition. These novel blood biomarkers of neurovascular unit are useful for identifying elderly individuals at risk of developing Alzheimer's disease.

Physiological role of K+ channels in irisin-induced vasodilation in rat thoracic aorta

Irisin, an exercise-induced myokine, has been shown to have a peripheral vasodilator effect. However, little is known about the mechanisms underlying its effects. In this study, it was aimed to investigate the vasoactive effects of irisin on rat thoracic aorta, and the hypothesis that voltage-gated potassium (KV) channels, ATP-sensitive potassium (KATP) channels, small-conductance calcium-activated potassium (SKCa) channels, large-conductance calcium-activated potassium (BKCa) channels, intermediate-conductance calcium-activated potassium (IKCa) channels, inward rectifier potassium (Kir) channels, and two-pore domain potassium (K2P) channels may have roles in these effects. Isometric contraction-relaxation responses of isolated thoracic aorta rings were measured with an organ bath model. The steady contraction was induced with both 10−5 M phenylephrine and 45 mM KCl, and then the concentration-dependent responses of irisin (10-9-10-6 M) were examined. Irisin exerted the vasorelaxant effects in both endothelium-intact and -denuded aortic rings at concentrations of 10-8, 10-7, and 10-6 M (p < 0.001). Besides, KV channel blocker 4-aminopyridine, KATP channel blocker glibenclamide, SKCa channel blocker apamin, BKCa channel blockers tetraethylammonium and iberiotoxin, IKCa channel blocker TRAM-34, and Kir channel blocker barium chloride incubations significantly inhibited the irisin-induced relaxation responses. However, incubation of K2P TASK-1 channel blocker anandamide did not cause a significant decrease in the relaxation responses of irisin. In conclusion, the first physiological findings were obtained regarding the functional relaxing effects of irisin in rat thoracic aorta. Furthermore, this study is the first to report that irisin-induced relaxation responses are associated with the activity of KV, KATP, SKCa, BKCa, IKCa, and Kir channels.

Proteomic Analysis of the Functional Inward Rectifier Potassium Channel (Kir) 2.1 Reveals Several Novel Phosphorylation Sites.

Membrane proteins represent a large family of proteins that perform vital physiological roles and represent key drug targets. Despite their importance, bioanalytical methods aiming to comprehensively characterize the post-translational modification (PTM) of membrane proteins remain challenging compared to other classes of proteins in part because of their inherent low expression and hydrophobicity. The inward rectifier potassium channel (Kir) 2.1, an integral membrane protein, is critical for the maintenance of the resting membrane potential and phase-3 repolarization of the cardiac action potential in the heart. The importance of this channel to cardiac physiology is highlighted by the recognition of several sudden arrhythmic death syndromes, Andersen-Tawil and short QT syndromes, which are associated with loss or gain of function mutations in Kir2.1, often triggered by changes in the β-adrenergic tone. Therefore, understanding the PTMs of this channel (particularly β-adrenergic tone-driven phosphorylation) is important for arrhythmia prevention. Here, we developed a proteomic method, integrating both top-down (intact protein) and bottom-up (after enzymatic digestion) proteomic analyses, to characterize the PTMs of recombinant wild-type and mutant Kir2.1, successfully mapping five novel sites of phosphorylation and confirming a sixth site. Our study provides a framework for future work to assess the role of PTMs in regulating Kir2.1 functions.

Kir4.1 Dysfunction in the Pathophysiology of Depression: A Systematic Review.

A serotonergic dysfunction has been largely postulated as the main cause of depression, mainly due to its effective response to drugs that increase the serotonergic tone, still currently the first therapeutic line in this mood disorder. However, other dysfunctional pathomechanisms are likely involved in the disorder, and this may in part explain why some individuals with depression are resistant to serotonergic therapies. Among these, emerging evidence suggests a role for the astrocytic inward rectifier potassium channel 4.1 (Kir4.1) as an important modulator of neuronal excitability and glutamate metabolism. To discuss the relationship between Kir4.1 dysfunction and depression, a systematic review was performed according to the PRISMA statement. Searches were conducted across PubMed, Scopus, and Web of Science by two independent reviewers. Twelve studies met the inclusion criteria, analyzing Kir4.1 relationships with depression, through in vitro, in vivo, and post-mortem investigations. Increasing, yet not conclusive, evidence suggests a potential pathogenic role for Kir4.1 upregulation in depression. However, the actual contribution in the diverse subtypes of the disorder and in the comorbid conditions, for example, the epilepsy-depression comorbidity, remain elusive. Further studies are needed to better define the clinical phenotype associated with Kir4.1 dysfunction in humans and the molecular mechanisms by which it contributes to depression and implications for future treatments.

Vasodilatory effects of betaine on isolated rat pulmonary artery rings.

The aim of this study was to investigate the vasodilatory effects of betaine, an alkaloid isolated from Lycium barbarum, on isolated pulmonary artery rings in rats and its possible mechanisms. Pulmonary vessels of normal Sprague-Dawley rats were isolated and pre-contracted using norepinephrine. Then, betaine was cumulatively added in differing concentrations (0.02-0.14 mg/mL), and the tension curve was observed and recorded. Changes in the tension of the pulmonary artery rings with an intact endothelium and a dissected endothelium were recorded. The interactions among betaine and NG-nitro-L-arginine methyl ester, indomethacin, 4-aminopyridine, barium chloride, and glibenclamide were evaluated. The experimental results show that betaine can relax the pulmonary artery rings pre-contracted by norepinephrine. Furthermore, pre-incubation with NG-nitro-L-arginine methyl ester and indomethacin did not inhibit betaine vasodilation, demonstrating that vasodilation by betaine is endothelium-dependent. Additionally, pretreatment of pulmonary artery rings with 4-aminopyridine and glibenclamide had no effect on betaine. However, pretreatment of pulmonary artery rings with barium chloride attenuated the effects of betaine. In conclusion, the vasodilatory effects of betaine on pulmonary artery rings is associated with inward rectifier potassium channels.

AGITATED, ALTERED, AND ELONGATED: THE RISKS OF DIPHENHYDRAMINE OVERDOSE

TOPIC: Critical Care TYPE: Medical Student/Resident Case Reports INTRODUCTION: Overdose has become a leading cause of injury-related death in the United States. Rapid recognition of a toxidrome is vital in determining management. CASE PRESENTATION: A young, unknown female was brought to the ED after being found agitated and combative. Evaluation was notable for tachycardia, mydriasis and diaphoresis. She received intramuscular diphenhydramine (DPH), haloperidol and lorazepam for agitation.She developed a wide QRS complex with polymorphic ventricular tachycardia (VT) concerning for Torsades de pointes, terminated by precordial thump. She was intubated for airway protection. Magnesium and sodium bicarbonate (NaHCO) pushes were administered for sustained monomorphic VT with return to sinus tachycardia. Electrocardiogram was significant for prolonged QTc of 607ms and QRS >150ms. Initial toxicology was negative for acetaminophen, salicylate and ethanol.NaHCO infusion with goal pH 7.5 to maintain a narrow QRS was started. She had persistently prolonged QT interval. Overdrive transcutaneous pacing was unsuccessful, so isoproterenol (IPN) infusion was started. NaHCO and IPN infusions were discontinued at 48 hours with no further arrhythmias. Extended toxicology screen was positive for DPH. On extubation, she endorsed consumption of >1.25g DPH. DISCUSSION: Classic anticholinergic symptoms of tachycardia, mydriasis and delirium are also the toxidrome for DPH overdose. Severe toxicity is observed after ingestion of >1.0g (1). Cardiac toxicity is exhibited as widening of QRS and QTc intervals (1-3). Similar to TCA overdose, QRS widening is manifested from blockade of the fast-closing myocardial sodium channels (2-3). Treatment for QRS widening with NaHCO is anecdotally recommended (2-3). In this case, bolus and infusion of NaHCO successfully shortened the patient's QRS duration. One case report suggested using lipid emulsion therapy(3); however, DPH intoxication was not suspected initially thereby limiting its use. Since presenting symptoms of DPH and anticholinergic toxicity overlap, physostigmine must be avoided due to QRS prolonging effects (2). This case reminds of cautious administration of the "B52" cocktail for agitated patients. The use of intravenous DPH, haloperidol and lorazepam can be used to calm acutely agitated or aggressive patients; yet, it should be avoided with unknown ingestions.Further, QT prolongation and polymorphic VT can result from DPH's ability to weakly block the delayed rectifier potassium channels (2). Traditionally resolving this includes overdrive pacing and magnesium supplementation, which were administered in this case. However, failed overdrive transcutaneous pacing led to IPN infusion to induce tachycardia-associated QTc shortening. CONCLUSIONS: High suspicion and familiarity with toxidromes can lead to early diagnosis and intervention for critically ill patients presenting with agitated altered mental status. REFERENCE #1: Radovanovic D, Meier PJ, Guirguis M, Lorent JP, Kupferschmidt H. Dose-dependent toxicity of diphenhydramine overdose. Hum Exp Toxicol. 2000 Sep;19(9):489-95. doi: 10.1191/096032700671040438 REFERENCE #2: Jang DH, Manini AF, Trueger NS, et al. Status epilepticus and wide-complex tachycardia secondary to diphenhydramine overdose. Clin Toxicol (Phila). 2010;48(9):945-948. doi:10.3109/15563650.2010.527850 REFERENCE #3: Abdi A, Rose E, Levine M. Diphenhydramine overdose with intraventricular conduction delay treated with hypertonic sodium bicarbonate and i.v. lipid emulsion. West J Emerg Med. 2014;15(7):855-858. doi:10.5811/westjem.2014.8.23407 DISCLOSURES: No relevant relationships by Joy Ayyoub, source=Web Response No relevant relationships by Lauren Catalano, source=Web Response No relevant relationships by Sydney Emerson, source=Web Response No relevant relationships by Shahrzad Zonoozi, source=Web Response

Novel inhibitors of the renal inward rectifier potassium channel of the mosquito vector Aedes aegypti.

The mosquito continues to be the most lethal animal to humans due to the devastating diseases that it carries and transmits. Controlling mosquito-borne diseases relies heavily on vector management using neurotoxic insecticides with limited modes of action. This has led to the emergence of resistance to pyrethroids and other neurotoxic insecticides in mosquitoes, which has reduced the efficacy of chemical control agents. Moreover, many neurotoxic insecticides are not selective for mosquitoes and negatively impact beneficial insectssuch as honeybees. Developing new mosquitocides with novel mechanisms of action is a clear unmet medical need; this review covers the efforts made toward this end by targeting the renal inward rectifier potassium channel (Kir) of the mosquito.

Atom based Profiling and Functional Enrichment analysis of Aquaporins

Sequence analysis is a computational biology method to study protein sequences by comparing amino acids of one protein sequence with the other (residual level comparison). This study reveals a new concept of comparing protein sequences at their basic atomic level. Aquaporins from various origin were compared at their atomic level and the study revealed that all the aquaporin proteins have a closed range of 31.0% to 34.2% of carbon atoms irrespective of their origin and amino acid sequence. Further the protein interaction and functional enrichment analysis of AQP7 showed significant interaction with glycerol kinase and ATP-sensitive inward rectifier potassium channel protein. Our insilico analysis on aquaporin proteins exposed that nature tends to maintain the overall carbon atom composition in the proteins regardless of their amino acid sequence composition which could be further used for their classification. Also, the most highly interacting partners for AQPs are the potassium buffering channel proteins.

MiR133b Microinjection during Early Development Targets Transcripts of Cardiomyocyte Ion Channels and Induces Oil-like Cardiotoxicity in Zebrafish (Danio rerio) Embryos.

Previous studies have shown that altered expression of a family of small noncoding RNAs (microRNAs, or miRs) regulates the expression of downstream mRNAs and is associated with diseases and developmental disorders. miR133b is highly expressed in mammalian cardiac and skeletal muscle, and aberrant expression is associated with cardiac disorders and electrophysiological changes in cardiomyocytes. Similarly, cardiac dysfunction has been observed in early life-stage mahi-mahi (Coryphaena hippurus) exposed to crude oil, a phenotype that has been associated with an upregulation of miR133b as well as subsequent downregulation of a delayed rectifier potassium channel (IKr) and calcium signaling genes that are important for proper heart development during embryogenesis. To examine the potential role of miR133b in oil-induced early life-stage cardiotoxicity in fish, cleavage-stage zebrafish (Danio rerio) embryos were either (1) microinjected with ∼3 nL of negative control miR (75 μM) or miR133b (75 μM) or (2) exposed to a treatment solution containing 5 μM benzo(a)pyrene (BaP), a model polycyclic aromatic hydrocarbon, as a positive control. At 72 h post fertilization (hpf), miR133b-injected fish exhibited BaP-like cardiovascular malformations, including a significantly increased pericardial area relative to negative control miR-injected embryos, as well as a significantly reduced eye area. qPCR revealed that miR133b microinjection decreased the abundance of cardiac-specific IKr kcnh6 at 5 hpf, which may contribute to action potential elongation in oil-exposed cardiomyocytes. Additionally, ryanodine receptor 2, a crucial calcium receptor in the sarcoplasmic reticulum, was also downregulated by miR133b. These results indicate that an oil-induced increase in miR133b may contribute to cardiac abnormalities in oil-exposed fish by targeting cardiac-specific genes essential for proper heart development.

Hypoxia with inflammation and reperfusion alters membrane resistance by dynamically regulating voltage-gated potassium channels in hippocampal CA1 neurons

Hypoxia typically accompanies acute inflammatory responses in patients and animal models. However, a limited number of studies have examined the effect of hypoxia in combination with inflammation (Hypo-Inf) on neural function. We previously reported that neuronal excitability in hippocampal CA1 neurons decreased during hypoxia and greatly rebounded upon reoxygenation. We attributed this altered excitability mainly to the dynamic regulation of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels and input resistance. However, the molecular mechanisms underlying input resistance changes by Hypo-Inf and reperfusion remained unclear. In the present study, we found that a change in the density of the delayed rectifier potassium current (IDR) can explain the input resistance variability. Furthermore, voltage-dependent inactivation of A-type potassium (IA) channels shifted in the depolarizing direction during Hypo-Inf and reverted to normal upon reperfusion without a significant alteration in the maximum current density. Our results indicate that changes in the input resistance, and consequently excitability, caused by Hypo-Inf and reperfusion are at least partially regulated by the availability and voltage dependence of KV channels. Moreover, these results suggest that selective KV channel modulators can be used as potential neuroprotective drugs to minimize hypoxia- and reperfusion-induced neuronal damage.

Fibroblast Growth Factor 21 Ameliorates NaV1.5 and Kir2.1 Channel Dysregulation in Human AC16 Cardiomyocytes.

Infarcted myocardium is predisposed to cause lethal ventricular arrhythmias that remain the main cause of death in patients suffering myocardial ischemia. Liver-derived fibroblast growth factor 21 (FGF21) is an endocrine regulator, which exerts metabolic actions by favoring glucose and lipids metabolism. Emerging evidence has shown a beneficial effect of FGF21 on cardiovascular diseases, but the role of FGF21 on ventricular arrhythmias following myocardial infarction (MI) in humans has never been addressed. This study was conducted to investigate the pharmacological effects of FGF21 on cardiomyocytes after MI in humans. Patients with arrhythmia in acute MI and healthy volunteers were enrolled in this study. Serum samples were collected from these subjects on day 1 and days 7–10 after the onset of MI for measuring FGF21 levels using ELISA. Here, we found that the serum level of FGF21 was significantly increased on day 1 after the onset of MI and it returned to normal on days 7–10, relative to the Control samples. In order to clarify the regulation of FGF21 on arrhythmia, two kinds of arrhythmia animal models were established in this study, including ischemic arrhythmia model (MI rat model) and nonischemic arrhythmia model (ouabain-induced guinea pig arrhythmia model). The results showed that the incidence and duration time of ischemic arrhythmias in rhbFGF21-treated MI rats were significantly reduced at different time point after MI compared with normal saline-treated MI rats. Moreover, the onset of the first ventricular arrhythmias was delayed and the numbers of VF and maintenance were attenuated by FGF21 compared to the rhbFGF21-untreated group in the ouabain model. Consistently, in vitro study also demonstrated that FGF21 administration was able to shorten action potential duration (APD) in hydrogen peroxide-treated AC16 cells. Mechanically, FGF21 can ameliorate the electrophysiological function of AC16 cells, which is characterized by rescuing the expression and dysfunction of cardiac sodium current (I Na) and inward rectifier potassium (I k1) in AC16 cells induced by hydrogen peroxide. Moreover, the restorative effect of FGF21 on NaV1.5 and Kir2.1 was eliminated when FGF receptors were inhibited. Collectively, FGF21 has the potential role of ameliorating transmembrane ion channels remodeling through the NaV1.5/Kir2.1 pathway by FGF receptors and thus reducing life-threatening postinfarcted arrhythmias, which provides new strategies for antiarrhythmic therapy in clinics.

Prediction of arrhythmia susceptibility through mathematical modeling and machine learning.

At present, the QT interval on the electrocardiographic (ECG) waveform is the most common metric for assessing an individual's susceptibility to ventricular arrhythmias, with a long QT, or, at the cellular level, a long action potential duration (APD) considered high risk. However, the limitations of this simple approach have long been recognized. Here, we sought to improve prediction of arrhythmia susceptibility by combining mechanistic mathematical modeling with machine learning (ML). Simulations with a model of the ventricular myocyte were performed to develop a large heterogenous population of cardiomyocytes (n = 10,586), and we tested each variant's ability to withstand three arrhythmogenic triggers: 1) block of the rapid delayed rectifier potassium current (IKr Block), 2) augmentation of the L-type calcium current (ICaL Increase), and 3) injection of inward current (Current Injection). Eight ML algorithms were trained to predict, based on simulated AP features in preperturbed cells, whether each cell would develop arrhythmic dynamics in response to each trigger. We found that APD can accurately predict how cells respond to the simple Current Injection trigger but cannot effectively predict the response to IKr Block or ICaL Increase. ML predictive performance could be improved by incorporating additional AP features and simulations of additional experimental protocols. Importantly, we discovered that the most relevant features and experimental protocols were trigger specific, which shed light on the mechanisms that promoted arrhythmia formation in response to the triggers. Overall, our quantitative approach provides a means to understand and predict differences between individuals in arrhythmia susceptibility.

Cardiac Na/Ca Exchange Suppression: A Late‐Breaking Knockout Story Showing That There Is No Free Lunch

Cardiac Na/Ca Exchange Suppression: A Late‐Breaking Knockout Story Showing That There Is No Free Lunch