Abstract
AIM:
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 ResultsqPCR analyses showed higher transcript levels of SK2 and SK3 than of the SK1 subtype in human atrial tissue. SK2 and SK3 were reduced in chronic atrial fibrillation (AF) compared to 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 depolarised 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 repolarisation. SK2 and SK3 were downregulated and had reduced functional importance in chronic AF. As SK current was not found to contribute substantially to the ventricular action potential, pharmacological inhibition of SK channels may be a putative atrial-selective target for future antiarrhythmic drug therapy.
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 ResultsqPCR analyses showed higher transcript levels of SK2 and SK3 than of the SK1 subtype in human atrial tissue. SK2 and SK3 were reduced in chronic atrial fibrillation (AF) compared to 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 depolarised 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 repolarisation. SK2 and SK3 were downregulated and had reduced functional importance in chronic AF. As SK current was not found to contribute substantially to the ventricular action potential, pharmacological inhibition of SK channels may be a putative atrial-selective target for future antiarrhythmic drug therapy.
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Cardiovascular Research |
| Vol/bind | 103 |
| Udgave nummer | 1 |
| Sider (fra-til) | 156-167 |
| Antal sider | 12 |
| ISSN | 0008-6363 |
| DOI | |
| Status | Udgivet - 1 jul. 2014 |