Figure 3.

When action potential duration has been prolonged previously by other means in dog papillary muscle (top panel), the positive feedback mechanism by which reduction of I_Kr (middle panel) and I_k1 (lower panel) further augments repolarization delay. Increased duration and thereby decreased rate of repolarization decreases the contribution of I_Kr and I_k1 currents to the repolarization process during the time course of the action potential, in turn producing a further slowing of repolarization. Numbers denote three recordings with different action potential durations. Dotted line identifies isochronal points on these recordings. I_Kr and I_k1 were measured from isolated ventricular myocytes subjected to action potential waveforms used as command signals in voltage-clamp conditions. AP, action potentials. Modified from Virág et al. (2009), with permission.