Left Ventricular Hypertrophy Decreases Slowly but Not Rapidly Activating Delayed Rectifier Potassium Currents of Epicardial and Endocardial Myocytes in Rabbits

Background—Delayed rectifier K+ currents are critical to action potential (AP) repolarization. The present study examines the effects of left ventricular hypertrophy (LVH) on delayed rectifier K+ currents and their contribution to AP repolarization in both epicardial (Epi) and endocardial (Endo) myocytes. Methods and Results—LVH was induced in rabbits by a 1-kidney removal, 1-kidney vascular clamping method. Slowly (IKs) and rapidly (IKr) activating delayed rectifier K+ currents were recorded by the whole-cell patch-clamp technique, and APs were recorded by the microelectrode technique. In normal rabbit left ventricular myocytes, IKs densities were larger in Epi than in Endo (1.1±0.1 versus 0.43±0.07 pA/pF), whereas IKr density was similar between Epi and Endo (0.31±0.05 versus 0.36±0.07 pA/pF) at 20 mV. LVH reduced IKs density to a similar extent (≈40%) in both Epi and Endo but had no significant effect on IKr in either Epi or Endo. Consequently, IKr was expected to contribute more to AP repolarization i...