Arrhythmia development during inhibition of small-conductance calcium-activated potassium channels in acute myocardial infarction in a porcine model

Abstract Aims Acute myocardial infarction (AMI) is associated with intracellular Ca2+ build-up. In healthy ventricles, small conductance Ca2+-activated K+ (SK) channels are present but do not participate in repolarization. However, SK current is increased in chronic myocardial infarction and heart failure, and recently, SK channel inhibition was demonstrated to reduce arrhythmias in AMI rats. Hence, we hypothesized that SK channel inhibitors (NS8593 and AP14145) could reduce arrhythmia development during AMI in a porcine model. Methods and results Twenty-seven pigs were randomized 1:1:1 to control, NS8593, or AP14145. Haemodynamic and electrophysiological parameters [electrocardiogram (ECG) and monophasic action potentials (MAP)] were continuously recorded. A balloon was placed in the mid-left anterior descending artery, blinded to treatment. Infusion lasted from 10 min before occlusion until 30 min after. Occlusion was maintained for 1 h, followed by 2 h of reperfusion. Upon occlusion, cardiac output dropped similarly in all groups, while blood pressure remained stable. Heart rate decreased in the NS8593 and AP14145 groups. QRS duration increased upon occlusion in all groups but more prominently in AP14145-treated pigs. Inhibition of SK channels did not affect QT interval. Infarct MAP duration shortened comparably in all groups. Ventricular fibrillation developed in 4/9 control-, 4/9 AP14145-, and 2/9 NS8593-treated pigs. Ventricular tachycardia was rarely observed in either group, whereas ventricular extrasystoles occurred comparably in all groups. Conclusion Inhibition of SK channels was neither beneficial nor detrimental to ventricular arrhythmia development in the setting of AMI in this porcine model.

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Ventricular tachyarrhythmias in rats with acute myocardial infarction involves activation of small-conductance Ca2+-activated K+ channels

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00820.2011 ◽

2013 ◽

Vol 304 (1) ◽

pp. H118-H130 ◽

Cited By ~ 47

Author(s):

Le Gui ◽

Zhiwei Bao ◽

Yinyu Jia ◽

Xiaotong Qin ◽

Zixi (Jack) Cheng ◽

...

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Channel Blocker ◽

Left Ventricular ◽

Dependent Manner ◽

Ventricular Tachyarrhythmias ◽

Sk Channels ◽

Sk Channel ◽

Small Conductance

In vitro experiments have shown that the upregulation of small-conductance Ca2+-activated K+ (SK) channels in ventricular epicardial myocytes is responsible for spontaneous ventricular fibrillation (VF) in failing ventricles. However, the role of SK channels in regulating VF has not yet been described in in vivo acute myocardial infarction (AMI) animals. The present study determined the role of SK channels in regulating spontaneous sustained ventricular tachycardia (SVT) and VF, the inducibility of ventricular tachyarrhythmias, and the effect of inhibition of SK channels on spontaneous SVT/VF and electrical ventricular instability in AMI rats. AMI was induced by ligation of the left anterior descending coronary artery in anesthetized rats. Spontaneous SVT/VF was analyzed, and programmed electrical stimulation was performed to evaluate the inducibility of ventricular tachyarrhythmias, ventricular effective refractory period (VERP), and VF threshold (VFT). In AMI, the duration and episodes of spontaneous SVT/VF were increased, and the inducibility of ventricular tachyarrhythmias was elevated. Pretreatment in the AMI group with the SK channel blocker apamin or UCL-1684 significantly reduced SVT/VF and inducibility of ventricular tachyarrhythmias ( P < 0.05). Various doses of apamin (7.5, 22.5, 37.5, and 75.0 μg/kg iv) inhibited SVT/VF and the inducibility of ventricular tachyarrhythmias in a dose-dependent manner. Notably, no effects were observed in sham-operated controls. Additionally, VERP was shortened in AMI animals. Pretreatment in AMI animals with the SK channel blocker significantly prolonged VERP ( P < 0.05). No effects were observed in sham-operated controls. Furthermore, VFT was reduced in AMI animals, and block of SK channels increased VFT in AMI animals, but, again, this was without effect in sham-operated controls. Finally, the monophasic action potential duration at 90% repolarization (MAPD90) was examined in the myocardial infarcted (MI) and nonmyocardial infarcted areas (NMI) of the left ventricular epicardium. Electrophysiology recordings showed that MAPD90 in the MI area was shortened in AMI animals, and pretreatment with SK channel blocker apamin or UCL-1684 significantly prolonged MAPD90 ( P < 0.05) in the MI area but was without effect in the NMI area or in sham-operated controls. We conclude that the activation of SK channels may underlie the mechanisms of spontaneous SVT/VF and suseptibility to ventricular tachyarrhythmias in AMI. Inhibition of SK channels normalized the shortening of MAPD90 in the MI area, which may contribute to the inhibitory effect on spontaneous SVT/VF and inducibility of ventricular tachyarrhythmias in AMI.

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P703The small conductance Ca2+-activated K+-channel inhibition tool compound AP14145 protected the guinea pig heart from ventricular arrhythmia during hypokalemia whereas dofetilide was pro-arrhythmic

European Heart Journal ◽

10.1093/eurheartj/ehz747.0308 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

B H Bentzen ◽

L Abildgaard ◽

N G Edvardsson ◽

U S Soerensen ◽

M Grunnet ◽

...

Keyword(s):

Guinea Pig ◽

Ventricular Arrhythmia ◽

Qt Interval ◽

Tolerability Profile ◽

Sk Channels ◽

Sk Channel ◽

Channel Inhibition ◽

Increased Risk ◽

Repolarization Reserve ◽

Small Conductance

Abstract Background Hypokalemia is commonly encountered in the clinic. Hypokalemia reduces the cardiac repolarization reserve and causes increases in intracellular calcium. This prolongs the QT-interval and increases the risk of ventricular arrhythmia; a risk that can be further exacerbated by concomitant administration of classical class 3 anti-arrhythmic agents. Small conductance Ca2+-activated K+-channels (SK-channels) are a promising new atrial selective target for treatment of atrial fibrillation (AF). Under physiological conditions SK channels play an insignificant role in ventricular repolarization. However, this might change under hypokalemia because of concomitant increases in intracellur calcium. Purpose To study the effects of SK channel inhibition with the tool compound AP14145 or ICA under hypokalemic conditions as compared to the class 3 anti-arrhythmic agent dofetilide and time matched controls (TMC). Methods Guinea pig hearts were isolated and retrogradely perfused with normokalemic (4.5 mM K+) Krebs-Henseleit solution, followed by perfusion with drug or vehicle control. The perfusion was then changed to hypokalemic solution (2.5 mM K+) in presence of drug for 20 min, followed by 20 min perfusion with normokalemic solution in presence of drug. A total of 24 animals were included in the study and randomly assigned to 4 groups: ICA, AP14145, dofetilide or TMC. QT-interval, ventricular effective refractory period, extra systoles and incidence of ventricular tachycardia (VT) or fibrillation (VF) were recorded for each perfusion period. Results Hypokalemia caused a small increase in QT-interval. Application of SK channel inhibitors did not cause further changes, whereas dofetilide prolonged QT compared to hypokalemia alone. During hypokalemia 3 out of 6 hearts in the TMC group developed VF (one spontaneously, two following S1S2 stimulation) whereas 4 out of 6 hearts developed VF in the dofetilide group (one spontaneously, three following S1S2 stimulation). In comparison only 1 heart out of 6 developed VF when treated with the SK channel inhibitor ICA (spontaneously) or AP14145 (following S1S2 stimulation). Conclusion Hypokalemia was associated with an increased risk of VF, an effect that was exaggerated by co-administration of dofetilide. In comparison, the structurally and functionally different SK channel inhibitors, ICA and AP14145, protected the heart from hypokalemia induced VF. These results with the tool compound AP14145 support that SK inhibition may be associated with a better safety and tolerability profile than dofetilide. Acknowledgement/Funding Innovation Fund Denmark

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Dendritic small conductance calcium-activated potassium channels activated by action potentials suppress EPSPs and gate spike-timing dependent synaptic plasticity

eLife ◽

10.7554/elife.30333 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 10

Author(s):

Scott L Jones ◽

Minh-Son To ◽

Greg J Stuart

Keyword(s):

Synaptic Plasticity ◽

Potassium Channels ◽

Action Potentials ◽

Pyramidal Neurons ◽

Receptor Activation ◽

Spike Timing ◽

Sk Channels ◽

Sk Channel ◽

Calcium Activated Potassium Channels ◽

Small Conductance

Small conductance calcium-activated potassium channels (SK channels) are present in spines and can be activated by backpropagating action potentials (APs). This suggests they may play a critical role in spike-timing dependent synaptic plasticity (STDP). Consistent with this idea, EPSPs in both cortical and hippocampal pyramidal neurons were suppressed by preceding APs in an SK-dependent manner. In cortical pyramidal neurons EPSP suppression by preceding APs depended on their precise timing as well as the distance of activated synapses from the soma, was dendritic in origin, and involved SK-dependent suppression of NMDA receptor activation. As a result SK channel activation by backpropagating APs gated STDP induction during low-frequency AP-EPSP pairing, with both LTP and LTD absent under control conditions but present after SK channel block. These findings indicate that activation of SK channels in spines by backpropagating APs plays a key role in regulating both EPSP amplitude and STDP induction.

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P699Mechanisms of action of the small conductance Ca2+-activated K+-channel modulator AP30663, a novel compound being developed for treatment of atrial fibrillation in man

European Heart Journal ◽

10.1093/eurheartj/ehz747.0304 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

S H Bomholtz ◽

R Simo-Vicens ◽

L Abildgaard ◽

N G Edvardsson ◽

U S Soerensen ◽

...

Keyword(s):

Atrial Fibrillation ◽

Guinea Pig ◽

Mechanism Of Action ◽

Allosteric Modulator ◽

Sk Channels ◽

Sk Channel ◽

Channel Inhibition ◽

Negative Allosteric Modulator ◽

Atrial Refractoriness ◽

Small Conductance

Abstract Background Small conductance Ca2+-activated K+-channels (SK-channels) are a promising new atrial selective target for treatment of atrial fibrillation (AF). AP30663 is a small molecule inhibitor of SK-channels that is effective in converting vernakalant-resistant AF in tachy-paced pigs. Detailed understanding of the molecular mechanism of AP30663 is important for the development of SK channel inhibition for use in man. Purpose To establish the electrophysiological profile, mechanism of action and efficacy in prolonging atrial refractoriness ex vivo of AP30663. Methods AP30663 potency and mechanism of action were established by whole cell and inside-out patch clamp recordings of expressed SK channels. The ion channel selectivity profile of AP30663 was investigated on heterologous expressed channels. Effects of AP30663 or vehicle (DMSO) on atrial refractoriness (AERP) and ventricular repolarization (QTcB) were investigated on isolated perfused guinea pig hearts. Results AP30663 was found to be a selective negative allosteric modulator of SK channels (IC50=0.77±x0.13 μM) with no or minor effects on a panel of other cardiac ion channels, including hERG/KV11.1, (IKr), KV7.1/KCNE1 (IKs), KV4.3/KChiP2 (Ito), Kir2.1 (IK1), Kir3.1/Kir3.4 (IKACh), KV1.5 (IKur), NaV1.5 (INa) and CaV1.2 (ICa). AP30663 inhibited the SK-channel by right-shifting the calcium activation curve of the SK-channel (the EC50 of Ca2+ increased from 0.43±0.02 μM (control, n=6) to 1.37±0.05 μM (in the presence of 7μM AP30663, n=6). In isolated guinea pig hearts, administration of vehicle had no effect on AERP or QTcB. AP30663 significantly prolonged the AERP in 3 μM (to 131±6% of baseline) and 10 μM (to 165±3% of baseline) without any effects on the QTcB. Conclusion AP30663 is a selective negative allosteric modulator of SK channels, acting by means of shifting the calcium dependence of SK-channel activation. AP30663 prolonged atrial refractoriness without affecting the QT-interval in isolated perfused heart preparations. These properties support continued development of AP30663 for treatment of AF in man. Acknowledgement/Funding Innovation Fund Denmark, Wellcome Trust

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Downregulation of Purkinje Cell Activity by Modulators of Small Conductance Calcium-Activated Potassium Channels In Rat Cerebellum

Acta Naturae ◽

10.32607/20758251-2016-8-4-91-99 ◽

2016 ◽

Vol 8 (4) ◽

pp. 91-99 ◽

Cited By ~ 4

Author(s):

T. V. Karelina ◽

Yu. D. Stepanenko ◽

P. A. Abushik ◽

D. A. Sibarov ◽

S. M. Antonov

Keyword(s):

Potassium Channels ◽

Purkinje Cell ◽

Cell Activity ◽

Spike Frequency ◽

Specific Marker ◽

Sk Channels ◽

Simple Spike ◽

Sk Channel ◽

Calcium Activated Potassium Channels ◽

Small Conductance

Small-conductance calcium-activated potassium channels (SK channels) are widely expressed in CNS tissues. Their functions, however, have not been well studied. Participation of SK channels in Purkinje cell (PC) pacemaker activity has been studied predominantly in vitro. Here we studied for the first time the effects of SK channel activation by NS309 or CyPPA on the PC simple spike frequency in vivo in adult (3 - 6 months) and aged (22 - 28 months) rats using extracellular microelectrode recordings. Both pharmacological agents caused a statistically significant decrease in the PC simple spike frequency. The maximum value of the decrease in the simple spike frequency did not depend on age, whereas a statistically significant inhibition of the spike frequency was achieved faster in aged animals than in adult ones. In experiments on cultured neurons PCs were identified by the expression of calbindin as the PC-specific marker. Registration of transmembrane currents in cerebellar neurons revealed the direct action of NS309 and CyPPA on the SK channels of PC consisted in the enhancement of outward potassium currents and action potential after-hyperpolarization. Thus, SK channel activators can compensate for age-related changes of the autorhythmic functions of the cerebellum.

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SK channel inhibition mediates the initiation and amplitude modulation of synchronized burst firing in the spinal cord

Journal of Neurophysiology ◽

10.1152/jn.00929.2016 ◽

2017 ◽

Vol 118 (1) ◽

pp. 161-175 ◽

Cited By ~ 1

Author(s):

Amr A. Mahrous ◽

Sherif M. Elbasiouny

Keyword(s):

Spinal Cord ◽

Amplitude Modulation ◽

Burst Firing ◽

Sk Channels ◽

Spinal Motoneurons ◽

Sk Channel ◽

Channel Inhibition ◽

Small Conductance ◽

Excitatory Drive

Burst firing in motoneurons represents the basis for generating meaningful movements. Neuromodulators and inhibitory receptor blocker cocktails have been used for years to induce burst firing in vitro; however, the ionic mechanisms in the motoneuron membrane that contribute to burst initiation and amplitude modulation are not fully understood. Small conductance Ca2+-activated potassium (SK) channels regulate excitatory inputs and firing output of motoneurons and interneurons and therefore, are a candidate for mediating bursting behavior. The present study examines the role of SK channels in the generation of synchronized bursting using an in vitro spinal cord preparation from adult mice. Our results show that SK channel inhibition is required for both initiation and amplitude modulation of burst firing. Specifically, administration of the synaptic inhibition blockers strychnine and picrotoxin amplified the spinal circuit excitatory drive but not enough to evoke bursting. However, when SK channels were inhibited using various approaches, the excitatory drive was further amplified, and synchronized bursting was always evoked. Furthermore, graded SK channel inhibition modulated the amplitude of the burst in a dose-dependent manner, which was reversed using SK channel activators. Importantly, modulation of neuronal excitability using multiple approaches failed to mimic the effects of SK modulators, suggesting a specific role for SK channel inhibition in generating bursting. Both NMDA ( N-methyl-d-aspartate) and AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionate) receptors were found to drive the synchronized bursts. The blocking of gap junctions did not disturb the burst synchrony. These results demonstrate a novel mechanistic role for SK channels in initiating and modulating burst firing of spinal motoneurons. NEW & NOTEWORTHY This study demonstrates that cholinergic inhibition or direct blockade of small conductance Ca2+-activated potassium (SK) channels facilitates burst firing in spinal motoneurons. The data provide a novel mechanistic explanation for synchronized bursting initiation and amplitude modulation through SK channel inhibition. Evidence also shows that synchronized bursting is driven by NMDA ( N-methyl-d-aspartate) and AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionate) receptors and that gap junctions do not mediate motoneuron synchronization in this behavior.

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Cardiac small-conductance calcium-activated potassium channels in health and disease

Pflügers Archiv - European Journal of Physiology ◽

10.1007/s00424-021-02535-0 ◽

2021 ◽

Vol 473 (3) ◽

pp. 477-489 ◽

Cited By ~ 1

Author(s):

Xiao-Dong Zhang ◽

Phung N. Thai ◽

Deborah K. Lieu ◽

Nipavan Chiamvimonvat

Keyword(s):

Ventricular Myocytes ◽

Pulmonary Veins ◽

Differential Sensitivity ◽

Sk Channels ◽

Sk Channel ◽

Ventricular Cells ◽

Intracellular Ca ◽

Life Threatening ◽

Health And Disease ◽

Small Conductance

AbstractSmall-conductance Ca2+-activated K+ (SK, KCa2) channels are encoded by KCNN genes, including KCNN1, 2, and 3. The channels play critical roles in the regulation of cardiac excitability and are gated solely by beat-to-beat changes in intracellular Ca2+. The family of SK channels consists of three members with differential sensitivity to apamin. All three isoforms are expressed in human hearts. Studies over the past two decades have provided evidence to substantiate the pivotal roles of SK channels, not only in healthy heart but also with diseases including atrial fibrillation (AF), ventricular arrhythmia, and heart failure (HF). SK channels are prominently expressed in atrial myocytes and pacemaking cells, compared to ventricular cells. However, the channels are significantly upregulated in ventricular myocytes in HF and pulmonary veins in AF models. Interests in cardiac SK channels are further fueled by recent studies suggesting the possible roles of SK channels in human AF. Therefore, SK channel may represent a novel therapeutic target for atrial arrhythmias. Furthermore, SK channel function is significantly altered by human calmodulin (CaM) mutations, linked to life-threatening arrhythmia syndromes. The current review will summarize recent progress in our understanding of cardiac SK channels and the roles of SK channels in the heart in health and disease.

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Abstract 17319: Distinct Effects of Human Calmodulinopathy on the Function of Small Conductance Ca 2+ -Activated K + (SK) Channels

Circulation ◽

10.1161/circ.138.suppl_1.17319 ◽

2018 ◽

Vol 138 (Suppl_1) ◽

Author(s):

Hannah A Ledford ◽

Seojin Park ◽

Duncan Muir ◽

Wen Smith ◽

Ryan L Woltz ◽

...

Keyword(s):

Ion Channels ◽

Intracellular Signaling ◽

Critical Role ◽

Dominant Negative ◽

Polymorphic Ventricular Tachycardia ◽

Dominant Negative Effect ◽

Sk Channels ◽

Channel Function ◽

Sk Channel ◽

Small Conductance

Background: Calmodulin (CaM) plays a critical role in intracellular signaling and regulation of Ca 2+ -dependent ion channels. Mutations in CALM1, CALM2, and CALM3 have recently been linked to cardiac arrhythmias, such as Long QT Syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia (CPVT), and familial idiopathic ventricular fibrillation (IVF). Small-conductance Ca 2+ - activated K + channels (SK) are voltage-independent channels that are regulated solely from beat-to-beat changes in intracellular calcium. CaM regulates the function of multiple ion channels, including SK channels, although the effect of CaM mutations on these channels is not yet understood. We hypothesize that human CaM mutations linked to sudden cardiac death disrupt SK channel function by distinct mechanisms. Methods and Results: We tested the effects of LQTS (CaM D96V , CaM D130G ), CPVT (CaM N54I , CaM N98S ), and IVF (CaM F90L ) CaM mutants compared to CaM WT on SK channel function. Using whole-cell voltage-clamp recordings, we found that CaM D96V and CaM D130G mutants significantly inhibited apamin-sensitive currents. Similarly, action potential studies in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) also revealed significant knockdown of apamin-sensitive currents. Immunofluorescent confocal microscopy confirmed that this effect was not due to changes in SK channel trafficking. Rather, co-immunoprecipitation studies showed a significant decrease in the association of these CaM mutants with the SK channel. Rosetta molecular modeling was used to identify a conformational change in CaM F90L structure compared to that of CaM WT . Conclusions: We found that CaM D96V and CaM D130G mutants significantly reduced apamin-sensitive currents, through a dominant negative effect on SK channel function. Consistent with our hypothesis, CaM F90L resulted in the least inhibitory effects. The data suggests that specific mutations with phenylalanine to leucine (CaM F90L ) may disrupt the interaction between apo-CaM with CaMBD on the SK2 channel.

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