Electrophysiological effects of small conductance Ca 2+ -activated K + channels in atrial myocytes

Abstract

Atrial fibrillation (AF), a cardiac arrhythmia characterized by an abnormal heart rythm originated in the atria, is one of the most prevalent cardiac diseases. Although it may have diverse causes, genetic screening has shown that a percentage of pacients suffering of AF present a genetic variant related to disregulation of calcium-activated potassium (SK) channels. In this paper we review the main characteristics of these channels and use several mathematical models of human atrial cardiomyocytes to study their influence in the form of the atrial action potential. We show that an overexpression of SK channels results in decreased action potential duration and, under some circumstances, it may give rise to alternans, suggesting a pro-arrhythmic role of this current. This effect becomes more important at higher pacing rates. Nevertheless, we also find it to protect against spontaneous calcium release induced afterdepolarizations, acting in this case as an antiarrhythmic factor.