Outward currents in hypertrophied feline ventricular myocytes

In the present study we have characterized the inward rectifying K current, I(K1), and the delayed rectifying outward current, I(X1), in single feline ventricular myocytes isolated from normal cats and animals with experimentally induced RVH. The ionic currents described in this study share many characteristics with the ionic currents first observed in multicellular preparations, but differ from them in several important respects, most notably the presence of a negative slope region in the background (IK1) current: voltage relationship and the relative insensitivity of I(X1) to block by traditional K channel blockers. These findings are similar to those reported for these currents in other preparations of single ventricular or Purkinje myocytes. The present study also demonstrates that there are several abnormalities of I(K1) and I(X1) in hypertrophied myocardium. The magnitude of I(K1) is larger in hypertrophy myocytes, while the magnitude of I(X1) is reduced. I(X1) showed steeper rectification, slower activation, and more rapid deactivation in hypertrophy myocytes, abnormalities which may contribute to the prolonged AP duration of hypertrophied myocardium. These findings, in addition to our previous report on alterations of the slow inward Ca current in hypertrophied myocardium, add to our understanding of the electrophysiologic derangements induced by pressure overload cardiac hypertrophy.