Reverse rate-dependent APD prolongation by IKr block (1 µmol·L−1 dofetilide), IK1 block (10 µmol·L−1 BaCl2), ICa activation (1 µmol·L−1 BAY-K 8644) and by INa activation (1 µg·mL−1 veratrine) in dog right ventricular papillary muscle. Note that the most prominent reverse rate-dependent APD lengthening was elicited by enhancement of ICa and INa. Data are expressed as mean ± SEM. APD, action potential duration; ICa, L-type Ca2+ current; IK1, inward rectifier potassium current; IKr, rapid component of the delayed rectifier potassium current; n, number of measurements.