Inhibition of SK channels prolongs atrial effective refractory period without affecting QT interval and prevents and terminates AF ex vivo and in vivo, thus offering a promising new therapeutic opportunity in the treatment of AF.

Background-Voltage-gated potassium (K ϩ ) channels encoded by KCNQ genes (Kv7 channels) have been identified in various rodent and human blood vessels as key regulators of vascular tone; however, nothing is known about the functional impact of these channels in vascular disease. We ascertained the effect of 3 structurally different activators of Kv7.2 through Kv7.5 channels (BMS-204352, S-1, and retigabine) on blood vessels from normotensive and hypertensive animals. Methods and Results-Precontracted thoracic aorta and mesenteric artery segments from normotensive rats were relaxed by all 3 Kv7 activators, with potencies of BMS-204352ϭS-1Ͼretigabine. We also tested these agents in the coronary circulation using the Langendorff heart preparation. BMS-204352 and S-1 dose dependently increased coronary perfusion at concentrations between 0.1 and 10 mol/L, whereas retigabine was effective at 1 to 10 mol/L. In addition, S-1 increased K ϩ currents in isolated mesenteric artery myocytes. The ability of these agents to relax precontracted vessels, increase coronary flow, or augment K ϩ currents was impaired considerably in tissues isolated from spontaneously hypertensive rats (SHRs). Of the 5 KCNQ genes, only the expression of KCNQ4 was reduced (Ϸ3.7 fold) in SHRs aorta. Kv7.4 protein levels were Ϸ50% lower in aortas and mesenteric arteries from spontaneously hypertensive rats compared with normotensive vessels. A similar attenuated response to S-1 and decreased Kv7.4 were observed in mesenteric arteries from mice made hypertensive by angiotensin II infusion compared with normotensive controls. Conclusions-In 2 different rat and mouse models of hypertension, the functional impact of Kv7 channels was dramatically downregulated. (Circulation. 2011;124:602-611.)Key Words: hypertension Ⅲ vasodilation Ⅲ KCNQ potassium channels Ⅲ gene expression P rimary hypertension is characterized by raised total peripheral resistance caused by increased arterial tone. 1 Evidence suggests increased vascular tone during hypertension is a result of a more depolarized membrane potential, which has been associated with a rise in intracellular calcium (Ca 2ϩ ). 2,3 As such, an understanding of the K ϩ channels that stabilize the resting membrane potential is crucial for delineating the pathogenesis of hypertension. Clinical Perspective on p 611KCNQ1-5 genes encode for voltage-gated K ϩ channels (Kv7.1 through Kv7.5, respectively) that have an established physiological role in neurons, 4 -7 cardiomyocytes, 8 cochlea, 9 and some epithelia. 10 There is now a growing appreciation that Kv7 channels are important regulators of smooth muscle contractility in rodent and human blood vessels. [11][12][13] In all blood vessels studied, KCNQ1 and KCNQ4 expression appears to dominate, 11,12,14 -18 although our laboratory has shown a truncated variant of KCNQ5 is also readily expressed. 15,19 Modulation of these channels provokes profound changes in vascular smooth muscle membrane potential and consequently vascular tone. [13][14][15][16][17]20 Thus, the non...

We have identified and characterized the compound NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) as a potent activator of human Ca2+ -activated K+ channels of SK and IK types, whereas it is devoid of effect on BK type channels. IK- and SK-channels have previously been reported to be activated by the benzimidazolinone, 1-EBIO and more potently by its dichloronated-analogue, DC-EBIO. NS309 is at least 1000 times more potent than 1-EBIO and at least 30 times more potent than DC-EBIO when the compounds are compared on the same cell.

Aim Transient outward potassium current (Ito) is thought to be central to the activator has not been pathogenesis of the Brugada syndrome (BrS). However, an Ito available with which to validate this hypothesis. Here we provide a direct test of the hypothesis using a novel Ito activator, NS5806. Methods Isolated canine ventricular myocytes and coronary-perfused wedge preparations were used. Results Whole-cell patch-clamp studies showed that NS5806 (10 μM) increased peak Ito at +40 mV by 79±4% (24.5±2.2 to 43.6±3.4 pA/pF, n=7) and slowed the time-constant increased of inactivation from 12.6±3.2 to 20.3±2.9 ms, n=7. Total charge carried by Ito by 186% (from 363.9 ± 40.0 to 1042.0 ± 103.5 pA ms/pF, n=7). In ventricular wedge preparations, NS5806 increased phase 1 and notch amplitude of the action potential (AP) in epicardium, but not endocardium, and accentuated the ECG J-wave, leading to the development of phase 2 reentry and polymorphic ventricular tachycardia (n=9). While sodium and calcium channel blockers are capable of inducing BrS only in right ventricular wedge preparations, the Ito activator was able to induce the phenotype in wedges from both ventricles. NS5806 induced BrS in 4/6 right and 2/10 left ventricular wedge preparations. Conclusions The Ito activator NS5806 recapitulates the electrographic and arrhythmic manifestation of BrS, providing evidence in support of its pivotal role in the genesis of the disease. Our findings also suggest that a genetic defect leading to a gain of function of Ito could explain variants of BrS in which ST-segment elevation or J-waves are evident in both right and left ECG leads.

The cardiac action potential is generated by a concerted action of different ion channels and transporters. Dysfunction of any of these membrane proteins can give rise to cardiac arrhythmias, which is particularly true for the repolarizing potassium channels. We suggest that an increased repolarization current could be a new antiarrhythmic principle, because it possibly would attenuate afterdepolarizations, ischemic leak currents, and reentry phenomena. Repolarization of the cardiac myocytes is crucially dependent on the late rapid delayed rectifier current (I Kr ) conducted by ether-a-go-go-related gene (ERG) potassium channels. We have developed the diphenylurea compound 1,3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea (NS1643) and tested whether this small organic molecule could increase the activity of human ERG (HERG) channels expressed heterologously. In Xenopus laevis oocytes, NS1643 increased both steady-state and tail current at all voltages tested. The EC 50 value for HERG channel activation was 10.5 M. These results were reproduced on HERG channels expressed in mammalian human embryonic kidney 293 cells. In guinea pig cardiomyocytes, studied by patch clamp, application of 10 M NS1643 activated I Kr and significantly decreased the action potential duration to 65% of the control values. The effect could be reverted by application of the specific HERG channel inhibitormethanesulfonanilide (E-4031) at 100 nM. Application of NS1643 also resulted in a prolonged postrepolarization refractory time. Finally, cardiomyocytes exposed to NS1643 resisted reactivation by small depolarizing currents mimicking early afterdepolarizations. In conclusion, HERG channel activation by small molecules such as NS1643 increases the repolarization reserve and presents an interesting new antiarrhythmic approach.The action potential initiates and controls the contraction of cardiac cells. The shape and duration of the action potential are the result of an ordered sequence of changes in membrane permeability to specific ions. The action potential duration (APD) and refractoriness are especially sensitive to the membrane permeability to potassium ions. Voltage-gated potassium channels are activated at different stages of the action potential, including the early transient outward current (I to ) and ultrarapid delayed rectifier current (I Kur ) as well as the late rapid delayed rectifier current (I Kr ) and slow delayed rectifier current (I Ks ) (Snyders, 1999). Most of the ion channels responsible for these currents will undergo inactivation during sustained depolarization. Release from inactivation is seen upon repolarization to the resting membrane potential. Inactivation is especially pronounced and fast for I Kr current. This implies that I Kr current contribution is almost negligible during the action potential plateau phase but very prominent during repolarization and the start of the diastolic interval. The large I Kr current at the early diastolic interval is a consequence of the slow deactivation kinetics of this...

Activation of the large-conductance Ca(2+)-activated K(+) channel (BK) in the cardiac inner mitochondrial membrane has been suggested to protect the heart against ischemic injury. However, these findings are limited by the low selectivity profile and potency of the BK channel activator (NS1619) used. In the present study, we address the cardioprotective role of BK channels using a novel, potent, selective, and chemically unrelated BK channel activator, NS11021. Using electrophysiological recordings of heterologously expressed channels, NS11021 was found to activate BK alpha + beta1 channel complexes, while producing no effect on cardiac K(ATP) channels. The cardioprotective effects of NS11021-induced BK channel activation were studied in isolated, perfused rat hearts subjected to 35 min of global ischemia followed by 120 min of reperfusion. 3 microM NS11021 applied prior to ischemia or at the onset of reperfusion significantly reduced the infarct size [control: 44.6 +/- 2.0%; NS11021: 11.4 +/- 2.0%; NS11021 at reperfusion: 19.8 +/- 3.3% (p < 0.001 for both treatments compared to control)] and promoted recovery of myocardial performance. Co-administration of the BK-channel inhibitor paxilline (3 microM) antagonized the protective effect. These findings suggest that tissue damage induced by ischemia and reperfusion can be reduced by activation of cardiac BK channels.

Within the field of new antiarrhythmic compounds, the interesting idea of activating human ether-a-go-go-related gene (HERG1) potassium channels has recently been introduced. Potentially, drugs that increase HERG1 channel activity will augment the repolarizing current of the cardiac myocytes and stabilize the diastolic interval. This may make the myocardium more resistant to events that cause arrhythmias. We here present the compound N- (4-bromo-2-(1H-tetrazol-5-yl)-phenyl)-NЈ-(3Ј-trifluoromethylphenyl)urea (NS3623), which has the ability to activate HERG1 channels expressed in Xenopus laevis oocytes with an EC 50 value of 79.4 M. Exposure of HERG1 channels to NS3623 affects the voltage-dependent release from inactivation, resulting in a half-inactivation voltage that is rightward-shifted by 17.7 mV. Moreover, the compound affects the time constant of inactivation, leading to a slower onset of inactivation of the macroscopic HERG1 currents. We also characterized the ability of NS3623 to increase the activity of different mutated HERG1 channels. The mutants S620T and S631A are severely compromised in their ability to inactivate. Application of NS3623 to any of these two mutants did not result in increased HERG1 current. In contrast, application of NS3623 to the mutant F656M increased HERG1 current to a larger extent than what was observed with wild-type HERG1 channels. Because the amino acid F656 is essential for highaffinity inhibition of HERG1 channels, it is concluded that NS3623 has a dual mode of action, being both an activator and an inhibitor of HERG1 channels. Finally, we show that NS3623 has the ability to shorten action potential durations in guinea pig papillary muscle.Potassium channels are essential for repolarizing the membrane potential of excitable cells and for maintaining the resting membrane potential between action potentials. In the heart, the delayed inward rectifying repolarizing potassium current I K is composed of two currents, denoted I Kr and I Ks . Activation of the human ether-a-go-go-related gene (HERG1) potassium channels underlies the I Kr (Sanguinetti et al., 1995;Trudeau et al., 1995), whereas the molecular component behind I Ks is KCNQ1 potassium channels in association with KCNE1 ␤-subunits (Barhanin et al., 1996;Sanguinetti et al., 1996). The HERG1 channel has an architecture like many other voltage-gated potassium channels with homologous subunits containing six transmembrane domains that form a tetrameric channel. In addition, the HERG1 channel is recognized by its characteristic inward rectification properties. The inward rectification is caused by the unique ability of the HERG1 channel to slowly activate at depolarized membrane potentials followed by much faster C-type inactivation where the channel keeps a nonconducting configuration . When the membrane repolarizes, the channel is quickly released from inactivation and conducts a slowly deactivating current. The pore region of the HERG1 channel has aromatic residues at positions 652 This work was supported by the...

Abstract-We have shown previously that inhibition of small conductance Ca 2ϩ -activated K ϩ (SK) channels is antiarrhythmic in models of acutely induced atrial fibrillation (AF). These models, however, do not take into account that AF derives from a wide range of predisposing factors, the most prevalent being hypertension. In this study we assessed the effects of two different SK channel inhibitors, NS8593 and UCL1684, in aging, spontaneously hypertensive rats to examine their antiarrhythmic properties in a setting of hypertension-induced atrial remodeling. Male spontaneously hypertensive rats and the normotensive Wistar-Kyoto rat strain were divided in 2ϫ3 groups of animals aged 3, 8, and 11 months, respectively. The animals were randomly assigned to treatment with NS8593, UCL1684, or vehicle, and open chest in vivo experiments including burst pacing-induced AF were performed. The aging spontaneously hypertensive rats were more vulnerable to AF induction both by S2 stimulation and burst pacing. Vehicle affected neither the atrial effective refractory period nor AF duration. SK channel inhibition with NS8593 and UCL1684 significantly increased the atrial effective refractory period and decreased AF duration in both the normotensive and hypertensive strains with no decline in efficacy as age increased. In conclusion, SK channel inhibition with NS8593 and UCL1684 possesses antiarrhythmic properties in a rat in vivo model of paroxysmal AF with hypertension-induced atrial remodeling. The present results support the notion that SK channels may offer a promising new therapeutic target in the treatment of AF.