Abstract 14021: Sarcoplasmic Reticulum Calcium Release is both Necessary and Sufficient for Activation of Small Conductance Calcium-activated Potassium Channels in Ventricular Myocytes
Introduction: Small conductance calcium-activated potassium (SK) channels are upregulated in human patients and animal models of heart failure. However, their activation mechanism and function in ventricular myocytes remain poorly understood. We aim to test the hypotheses that activation of SK channels in ventricular myocytes requires calcium release from sarcoplasmic reticulum (SR), and that SK currents contribute to reducing triggered activity.
Methods and Results: SK2 channels were overexpressed in adult rat ventricular myocytes using adenovirus gene transfer. Immuno-localization studies showed that overexpressed SK channels are distributed both at external sarcolemmal membranes and along the Z-lines, resembling the distribution of endogenous SK channels. Simultaneous patch clamp and confocal calcium imaging experiments in SK2-overexpressing cells demonstrated that depolarizing voltage steps resulted in transient outward currents sensitive to the specific SK channel inhibitor apamin. SR calcium release induced by rapid application of 10 mM caffeine evoked repolarizing SK currents, whereas complete depletion of SR calcium content eliminated SK currents in response to depolarizing voltage steps, despite intact calcium influx through L-type calcium channels. Furthermore, voltage-clamp experiments showed that SK channels can be activated by global spontaneous SR calcium release events known as calcium waves (SCWs). Current-clamp experiments revealed that SK overexpression shortens action potential duration (APD) and reduces the amplitude of delayed afterdepolarizations (DADs) resulting from SCWs.
Conclusions: SR calcium release is both necessary and sufficient for the activation of SK channels in rat ventricular myocytes. SK currents contribute to repolarization during action potentials and attenuate DADs driven by SCWs. Thus, SK upregulation in heart failure may have an anti-arrhythmic effect by shortening APD and reducing triggered activity.
- © 2013 by American Heart Association, Inc.