SK channel inhibitors NS8593 and ICAGEN decreased inwardly rectifying K+ currents by ~15% and prolonged action potential duration in atrial myocytes from sinus rhythm patients, but not AF patients.
Does SK channel inhibition alter action potential repolarization in human atrial tissue, and does this differ between sinus rhythm and chronic atrial fibrillation?
SK channels contribute to atrial repolarization in sinus rhythm but are down-regulated in chronic AF, highlighting them as a potential atrial-selective target for antiarrhythmic drugs.
AIMS: Small-conductance calcium-activated potassium (SK) channels are expressed in the heart of various species, including humans. The aim of the present study was to address whether SK channels play a functional role in human atria. METHODS AND RESULTS: Quantitative real-time PCR analyses showed higher transcript levels of SK2 and SK3 than that of the SK1 subtype in human atrial tissue. SK2 and SK3 were reduced in chronic atrial fibrillation (AF) compared with sinus rhythm (SR) patients. Immunohistochemistry using confocal microscopy revealed widespread expression of SK2 in atrial myocytes. Two SK channel inhibitors (NS8593 and ICAGEN) were tested in heterologous expression systems revealing ICAGEN as being highly selective for SK channels, while NS8593 showed less selectivity for these channels. In isolated atrial myocytes from SR patients, both inhibitors decreased inwardly rectifying K(+) currents by ∼15% and prolonged action potential duration (APD), but no effect was observed in myocytes from AF patients. In trabeculae muscle strips from right atrial appendages of SR patients, both compounds increased APD and effective refractory period, and depolarized the resting membrane potential, while only NS8593 induced these effects in tissue from AF patients. SK channel inhibition did not alter any electrophysiological parameter in human interventricular septum tissue. CONCLUSIONS: SK channels are present in human atria where they participate in repolarization. SK2 and SK3 were down-regulated and had reduced functional importance in chronic AF. As SK current was not found to contribute substantially to the ventricular AP, pharmacological inhibition of SK channels may be a putative atrial-selective target for future antiarrhythmic drug therapy.
Skibsbye et al. (Fri,) conducted a other in Atrial fibrillation. SK channel inhibitors (NS8593 and ICAGEN) was evaluated on Inwardly rectifying K(+) currents and action potential duration. SK channel inhibitors NS8593 and ICAGEN decreased inwardly rectifying K+ currents by ~15% and prolonged action potential duration in atrial myocytes from sinus rhythm patients, but not AF patients.
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