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...
BACKGROUND AND PURPOSEThe KCa3.1 channel is a potential target for therapy of immune disease. We identified a compound from a new chemical class of KCa3.1 inhibitors and assessed in vitro and in vivo inhibition of immune responses. EXPERIMENTAL APPROACHWe characterized the benzothiazinone NS6180 (4- [[3-(trifluoromethyl)phenyl]methyl]-2H-1,4-benzothiazin-3(4H)-one) with respect to potency and molecular site of action on KCa3.1 channels, selectivity towards other targets, effects on T-cell activation as well as pharmacokinetics and inflammation control in colitis induced by 2,4-dinitrobenzene sulfonic acid, a rat model of inflammatory bowel disease (IBD). KEY RESULTSNS6180 inhibited cloned human KCa3.1 channels (IC50 = 9 nM) via T250 and V275, the same amino acid residues conferring sensitivity to triarylmethanes such as like TRAM-34. NS6180 inhibited endogenously expressed KCa3.1 channels in human, mouse and rat erythrocytes, with similar potencies (15-20 nM). NS6180 suppressed rat and mouse splenocyte proliferation at submicrolar concentrations and potently inhibited IL-2 and IFN-g production, while exerting smaller effects on IL-4 and TNF-a and no effect on IL-17 production. Antibody staining showed KCa3.1 channels in healthy colon and strong up-regulation in association with infiltrating immune cells after induction of colitis. Despite poor plasma exposure, NS6180 (3 and 10 mg·kg -1 b.i.d.) dampened colon inflammation and improved body weight gain as effectively as the standard IBD drug sulfasalazine (300 mg·kg -1 q.d.).
Background and purpose: Large‐conductance Ca2+‐activated K+ channels (BKCa), located on the arterial and corporal smooth muscle, are potential targets for treatment of erectile dysfunction (ED). This study investigated whether NS11021 (1‐(3,5‐Bis‐trifluoromethyl‐phenyl)‐3‐[4‐bromo‐2‐(1H‐tetrazol‐5‐yl)‐phenyl]‐thiourea), a novel opener of BKCa channels, relaxes erectile tissue in vitro and enhances erectile responses in intact rats. The effects were compared with sildenafil, an inhibitor of phosphodiesterase type 5. Experimental approach: Patch clamp was used to record whole cell current in rat isolated corpus cavernosum smooth muscle cells (SMCs) and human umbilical vein endothelial cells (HUVECs). Isometric tension was measured in intracavernous arterial rings and corpus cavernosum strips isolated from rats and men, and simultaneous measurements of intracellular Ca2+ concentration ([Ca2+]i) and tension were performed in intracavernous arteries. Erectile response was measured in anaesthetized rats. Key results: In patch clamp recordings, NS11021 increased currents sensitive to the selective BKCa channel blocker, iberiotoxin (IbTX) in SMCs, but did not modulate K+ current in HUVECs. NS11021 reduced [Ca2+]i and tension in penile arteries. IbTX inhibited the vasorelaxation induced by NS11021 and sildenafil in human erectile tissue. NS11021 and sildenafil but not vehicle increased erectile responses in anaesthetized rats, an effect which was abolished after pretreatment with tetraethylammonium. Conclusions and implications: NS11021 leads to relaxation of both intracavernous arteries and corpus cavernosum strips primarily through opening of BKCa channels. It is also effective in facilitating erectile responses in anaesthetized rats. These results suggest a potential for use of BKCa openers in the treatment of ED.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.