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Association of Small-Conductance Calcium-Activated Potassium Channels and Atrial Fibrillation - How Far Have We Gone?

ABSTRACT: UNLABELLED:Atrial fibrillation (AF) is the most common sustained and most important arrhythmia in clinical practice. The mechanisms underlying AF initiation and maintenance are known to be complex and heterogeneous. The general understanding of the detailed molecular basis of AF is still incomplete. Recently, these is increasing evidence that small conductance calcium-activated potassium (SK) channels are associated with atrial action potential repolarization and the pathogenesis of AF. Although the functional role of SK channels in the genesis of AF is not entirely clear, new insights into the basic pathophysiological mechanism of AF have been provided. Besides, genome-wide association studies also implicate that genes coding for SK channels are related to the risk of developing AF. This article reviews recent work on the association of SK channels and AF, genetic studies of SK channels, and discuss future investigation and developments regarding this field. KEY WORDS:Atrial fibrillation; Genetics; Small conductance calcium-activated potassium channels.

SUBMITTER: Chang SH

PROVIDER: S-EPMC4804815 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature

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Association of Small-Conductance Calcium-Activated Potassium Channels and Atrial Fibrillation - How Far Have We Gone?

Chang Shu-Hsuan SH Chang Sheng-Nan SN Lin Lian-Yu LY Lai Ling-Ping LP Tseng Chuen-Den CD Wang Yi-Chih YC Yu Chih-Chieh CC Chiang Fu-Tien FT Hwang Juey-Jen JJ Lin Jiunn-Lee JL Tsai Chia-Ti CT

Acta Cardiologica Sinica 20140101 1

<h4>Unlabelled</h4>Atrial fibrillation (AF) is the most common sustained and most important arrhythmia in clinical practice. The mechanisms underlying AF initiation and maintenance are known to be complex and heterogeneous. The general understanding of the detailed molecular basis of AF is still incomplete. Recently, these is increasing evidence that small conductance calcium-activated potassium (SK) channels are associated with atrial action potential repolarization and the pathogenesis of AF. ...[more]

PMID: 27122762

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Project description:1. Nine bis-quinolinyl and bis-quinolinium compounds related to dequalinium, and previously shown to block apamin-sensitive small conductance Ca(2+)-activated K(+) channels (SK(Ca)), have been tested for their inhibitory effects on actions mediated by intermediate conductance Ca(2+)-activated K(+) channels (IK(Ca)) in rabbit blood cells. 2. In most experiments, a K(+)-sensitive electrode was employed to monitor the IK(Ca)-mediated net loss of cell K(+) that followed the addition of the Ca(2+) ionophore A23187 (2 microM) to red cells suspended at an haematocrit of 1% in a low K(+) (0.12 - 0.17 mM) solution. The remainder used an optical method based on measuring the reduction in light transmission that occurred on applying A23187 (0.4 or 2 microM) to a very dilute suspension of red cells (haematocrit 0.02%). 3. Of the compounds tested, the most potent IK(Ca) blocker was 1,12 bis[(2-methylquinolin-4-yl)amino]dodecane (UCL 1407) which had an IC(50) of 0.85+/-0.06 microM (mean+/-s.d. mean). 4. The inhibitory action of UCL 1407 and its three most active congeners was characterized by (i) a Hill slope greater than unity, (ii) sensitivity to an increase in external [K(+)], and (iii) a time course of onset that suggested use-dependence. Also, the potency of the nonquaternary compounds tested increased with their predicted lipophilicity. These findings suggested that the IK(Ca) blocking action resembles that of cetiedil rather than of clotrimazole. 5. Some quaternized members of the series were also active. The most potent was the monoquaternary UCL 1440 ((1-[N-[1-(3, 5-dimethoxybenzyl)-2-methylquinolinium-4-yl]amino]-10-[N'-(2-me thylqu inolinium-4yl)amino] decane (trifluoroacetate) which had an IC(50) of 1.8+/-0.1 microM. The corresponding bisquaternary UCL 1438 (1, 10-bis[N-[1-(3,5-dimethoxybenzyl)-2-methylquinolinium-4-yl]amino] decane bis(trifluoroacetate) was almost as active (IC(50) 2.7+/-0.3 microM). 6. A bis-aminoquinolium cyclophane (UCL 1684) had little IK(Ca) blocking action despite its great potency at SK(Ca) channels (IC(50) 4.1+/-0.2 nM). 7. The main outcome is the identification of new intermediate-conductance Ca(2+)-activated K(+) channel blockers with a wide range of IK(Ca)/SK(Ca) selectivities.

Project description:Background and purposeControlling vascular tone involves K(+) efflux through endothelial cell small- and intermediate-conductance calcium-activated potassium channels (K(Ca)2.3 and K(Ca)3.1, respectively). We investigated the expression of these channels in astrocytes and the possibility that, by a similar mechanism, they might contribute to neurovascular coupling.Experimental approachTransgenic mice expressing enhanced green fluorescent protein (eGFP) in astrocytes were used to assess K(Ca)2.3 and K(Ca)3.1 expression by immunohistochemistry and RT-PCR. K(Ca) currents in eGFP-positive astrocytes were determined in situ using whole-cell patch clamp electrophysiology. The contribution of K(Ca)3.1 to neurovascular coupling was investigated in pharmacological experiments using electrical field stimulation (EFS) to evoke parenchymal arteriole dilatation in FVB/NJ mouse brain slices and whisker stimulation to evoke changes in cerebral blood flow in vivo, measured by laser Doppler flowmetry.Key resultsK(Ca)3.1 immunoreactivity was restricted to astrocyte processes and endfeet and RT-PCR confirmed astrocytic K(Ca)2.3 and K(Ca)3.1 mRNA expression. With 200 nM [Ca(2+)](i) , the K(Ca)2.1-2.3/K(Ca)3.1 opener NS309 increased whole-cell currents. CyPPA, a K(Ca)2.2/K(Ca)2.3 opener, was without effect. With 1 µM [Ca(2+)](i) , the K(Ca)3.1 inhibitor TRAM-34 reduced currents whereas apamin (K(Ca)2.1-2.3 blocker) had no effect. CyPPA also inhibited currents evoked by NS309 in HEK293 cells expressing K(Ca)3.1. EFS-evoked Fluo-4 fluorescence confirmed astrocyte endfoot recruitment into neurovascular coupling. TRAM-34 inhibited EFS-evoked arteriolar dilatation by 50% whereas charybdotoxin, a blocker of K(Ca)3.1 and the large-conductance K(Ca) channel, K(Ca)1.1, inhibited dilatation by 82%. TRAM-34 reduced the cortical hyperaemic response to whisker stimulation by 40%.Conclusion and implicationsAstrocytes express functional K(Ca)3.1 channels, and these contribute to neurovascular coupling.

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Association of Small-Conductance Calcium-Activated Potassium Channels and Atrial Fibrillation - How Far Have We Gone?

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Association of Small-Conductance Calcium-Activated Potassium Channels and Atrial Fibrillation - How Far Have We Gone?

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