Biology subjects

Furutani, K.

Publications and source records attributed to Furutani, K..

6 recordsLinked to original sources

bioRxiv2026

A hERG Blocker Facilitates K+ Channel Current by Agonizing Pore Opening while Blocking

Many drugs that block voltage-gated K+ channels encoded by the human Ether-a-go-go-Related Gene (hERG) can cause long QT syndrome and life-threatening cardiac arrhythmias, yet the molecular mechanisms that determine this risk remain unclear. A process that may counteract arrhythmogenic hERG block, termed facilitation, is common to many clinically-approved hERG blockers including nifekalant, amiodarone, promethazine, imipramine, nortriptyline, haloperidol, verapamil, carvedilol, metoprolol, propranolol, quinidine, fluoxetine, and chlorpheniramine. Facilitation is an increase in hERG current, under certain conditions, due to these blockers. Here, we propose that an agonism-while-blocking mechanism undergirds facilitation. We focus on nifekalant, a Class III antiarrhythmic drug and exemplar hERG blocker that induces facilitation. We tested the hypothesis that nifekalant opens hERG channel gates while blocking, and that unblock of these open-yet-blocked channels results in supranormal hERG current. We develop rate-theory kinetic models to identify features of agonism-while-blocking that produce facilitation. We generate atomistic models that predict that nifekalant blocks the hERG conduction path while modulating the intracellular conduction gate. Voltage-clamp measurements reveal that agonism-while-blocking undergirds nifekalant block and facilitation. We speculate that this agonism-while-blocking mechanism contributes to the relative safety of hERG blockers that induce facilitation.

pharmacology and toxicology↗

bioRxiv2024

Distinct roles of general anesthesia activated CeA neurons in acute versus late phase of neuropathic pain

A previous study discovered a distinct population of GABAergic neurons in the central amygdala (CeA) that can be activated by general anesthesia (CeAGA) and exert analgesic functions (Hua et al., 2020). To independently reproduce these prior findings and to investigate the electrophysiological properties of CeAGA neurons, we first used 1.2% isoflurane to induce c-Fos activation in the mouse brain and validated the Fos expression by RNAscope in situ hybridization. Indeed, isoflurane induced robust Fos expression in CeA and these Fos+ CeAGA neurons are GABAergic neurons (Vgat+). We next used Fos-TRAP2 method (different from the CANE method used in the prior study) to label CeAGA neurons (tdTomato+). Our ex vivo electrophysiological recordings in brain slices revealed that compared to Fos-negative CeA neurons, CeAGA neurons had significantly higher excitability and exhibited distinct patterns of action potentials. Chemogenetic activation of Fos-TRAPed CeAGA neurons was effective at increasing pain thresholds in naive mice and mice with early-phase neuropathic pain 2 weeks after spared nerve injury (SNI). However, the same chemogenetic activation of CeAGA neurons only had modest analgesia in the late phase of SNI at 8 weeks, although it was highly effective in reducing chronic pain-associated anxiety behaviors at this stage. We found that Fos-negative CeA neurons, but not CeAGA neurons, exhibited increased excitability in the late-phase of SNI, suggesting that chronic pain causes a shift in the relative activity of the CeA microcircuit. Interestingly, Fos-negative neurons exhibited much higher expression of K+-Cl- cotransporter-2 (KCC2), and KCC2 expression was downregulated in the CeA in the late-phase of neuropathic pain. These results support the idea that targeting CeAGA neurons may provide therapeutic benefits for pain relief and chronic pain-associated anxiety. Our findings also suggest distinct roles of CeAGA neurons in regulating physiological pain, acute pain, and chronic pain with a possible involvement of KCC2.

neuroscience↗

bioRxiv2022

Facilitation by a hERG blocker is induced by pore opening and operates by pore reopening

A drug that blocks the cardiac myocyte voltage-gated K+ channels encoded by the human Ether-a-go-go-Related Gene (hERG) carries a potential risk of long QT syndrome and life-threatening cardiac arrhythmia, including Torsade de Points. Interestingly, certain hERG blockers can also facilitate hERG activation to increase hERG currents, which may reduce proarrhythmic potential. However, the molecular mechanism involved in the facilitation effect of hERG blockers remains unclear. The hallmark feature of the facilitation effect by hERG blockers is that a depolarizing preconditioning pulse shifts voltage-dependence of hERG activation to more negative voltages. Here we utilize a D540K hERG mutant to study the mechanism of the facilitation effect. D540K hERG is activated by not only depolarization but also hyperpolarization. This unusual gating property of the D540K hERG channel enables testing of hypotheses about the mechanism by which voltage induces facilitation of hERG by blockers. With D540K hERG, we find that nifekalant, a hERG blocker and Class III antiarrhythmic agent, facilitates not only current activation by depolarization but also current activation by hyperpolarization. Our results indicate that induction of facilitation is coupled to pore opening, not voltage per se. We propose that a gated-access mechanism is involved in the voltage-dependence of induction of facilitation. This study provides a molecular mechanism for modulation of hERG channels by nifekalant, a clinically important antiarrhythmic agent. Significance statementNifekalant is a clinically important antiarrhythmic agent and a hERG blocker which can also facilitate voltage-dependent activation of hERG channels after a preconditioning pulse. Here we show that the mechanism of action of the preconditioning pulse is to open a conductance gate to enable drug access to a facilitation site. Moreover, we find that facilitation increases hERG currents by altering pore dynamics, rather than acting through voltage sensors.

pharmacology and toxicology↗

bioRxiv2021

PD-1 in hippocampal neurons regulates excitability, synaptic plasticity, and cognition

Immunotherapy using monoclonal antibodies against programmed cell death protein 1 (PD-1) demonstrated improved survival in cancer patients through immune activation. Here we show that functional PD-1 is expressed in mouse and primate hippocampal neurons and PD-1 inhibition improves cognition in physiological and pathological conditions. Mice lacking the Pdcd1 gene encoding PD-1 exhibit enhanced long-term potentiation (LTP) and learning and memory. These behavioral and cellular changes can be recapitulated by selective deletion of Pdcd1 in hippocampal excitatory neurons but not in microglia. Perfusion of mouse or nonhuman primate brain slices with anti-PD-1 antibody is sufficient to increase excitability in CA1 hippocampal neurons. Conversely, re-expression of Pdcd1 in PD-1 deficient hippocampal neurons suppresses memory and LTP. Traumatic brain injury impairs learning and memory, which is improved by intraventricular administration of anti-PD-1. These findings suggest that anti-PD-1 treatment has therapeutic potential to counteract cognitive decline. HighlightsO_LIAdult mice lacking Pdcd1 in hippocampal neurons exhibit enhanced memory and LTP C_LIO_LIAnti-PD-1 antibody treatment increases CA1 neuron excitability in brain slices of mice and primates C_LIO_LIRe-expression of Pdcd1 in PD-1 deficient hippocampal neurons impairs memory and LTP C_LIO_LICognitive deficits after traumatic brain injury are improved by anti-PD-1 treatment C_LI

neuroscience↗

bioRxiv2021

Structural modeling of the hERG potassium channel and associated drug interactions

The voltage-gated potassium channel, KV11.1, encoded by the human Ether-a-go-go- Related Gene (hERG) is expressed in cardiac myocytes, where it is crucial for the membrane repolarization of the action potential. Gating of hERG channel is characterized by rapid, voltage-dependent, C-type inactivation, which blocks ion conduction and is suggested to involve constriction of the selectivity filter. Mutations S620T and S641A/T within the selectivity filter region of hERG have been shown to alter the voltage- dependence of channel inactivation. Because hERG channel blockade is implicated in drug-induced arrhythmias associated with both the open and inactivated states, we used Rosetta to simulate effects of hERG S620T and S641A/T mutations to elucidate conformational changes associated with hERG channel inactivation and differences in drug binding between the two states. Rosetta modeling of the S641A fast-inactivating mutation revealed a lateral shift of F627 side chain in the selectivity filter into the central channel axis along the ion conduction pathway and formation of four lateral fenestrations in the pore. Rosetta modeling of the non-inactivating mutations S620T and S641T suggested a potential molecular mechanism preventing F627 side chain from shifting into the ion conduction pathway during the proposed inactivation process. Furthermore, we used Rosetta docking to explore the binding mechanism of highly selective and potent hERG blockers - dofetilide, terfenadine, and E4031. Our structural modeling correlate well with existing experimental evidence involving interactions of these drugs with key hERG residues Y652 and F656 inside the pore and reveal potential ligand binding interactions within fenestration region in an inactivated state. Significance StatementComputational models of hERG potassium channel provide structural insights into an inactivated state and associated drug interactions. Our computational approach will be useful to study ion channel modulation by small molecules.

biophysics↗

bioRxiv2018

Facilitation of hERG channels by blockers: a mechanism predicted to reduce lethal cardiac arrhythmias

Fatal cardiac arrhythmias are caused by some, but not all, drugs that inhibit the cardiac rapid delayed-rectifier current (IKr) by blocking hERG channels. Here, we propose a novel mechanism that could make certain hERG blockers less proarrhythmic. Several drugs that block hERG channels, yet have favorable cardiac safety profiles, also evoke another effect; they increase the current amplitude upon low-voltage depolarization (facilitation). Voltage-clamp recordings of hERG block and facilitation by nifekalant, a Class III antiarrhythmic agent, constrained a model of human cardiac IKr. In human ventricular action potential simulations, nifekalant showed its therapeutic ability to suppress ectopic excitations, with or without facilitation. Without facilitation, excessive IKr block evoked early afterdepolarizations, which cause lethal arrhythmias. Facilitation prevented early afterdepolarizations at the same degree of block by increasing IKr during repolarization phase of action potentials. Thus, facilitation is proposed to reduce the arrhythmogenic risk of hERG blockers.\n\nAbbreviationsAP: action potential; APD: action potential duration; APD90: action potential duration measured at 90% repolarization; EAD: early afterdepolarization; hERG: human ether-ago-go-related gene; ICaL: L-type Ca2+ channel current; Inet: net ionic current; IK1: inward-rectifier potassium current; IKr: rapid component of the delayed-rectifier potassium current; INa: sodium current; ORd: OHara-Rudy dynamic

pharmacology and toxicology↗