Left ventricular hypertrophy in rabbits decreased slowly activating delayed rectifier K+ current density by approximately 40% and increased the propensity for early afterdepolarizations.
Does left ventricular hypertrophy alter delayed rectifier potassium currents and action potential repolarization in rabbit ventricular myocytes?
Left ventricular hypertrophy decreases slowly activating delayed rectifier potassium currents, increasing the risk of early afterdepolarizations, particularly in the endocardium.
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: VH was induced in rabbits by a 1-kidney removal, 1-kidney vascular clamping method. Slowly (I(Ks)) and rapidly (I(Kr)) 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, I(Ks) densities were larger in Epi than in Endo (1.1+/-0.1 versus 0.43+/-0.07 pA/pF), whereas I(Kr) density was similar between Epi and Endo (0.31+/-0.05 versus 0.36+/-0.07 pA/pF) at 20 mV. LVH reduced I(Ks) density to a similar extent (approximately 40%) in both Epi and Endo but had no significant effect on I(Kr) in either Epi or Endo. Consequently, I(Kr) was expected to contribute more to AP repolarization in LVH than in control. This was confirmed by specific I(Kr) block with dofetilide, which prolonged AP significantly more in LVH than in control (31+/-3% versus 18+/-2% in Epi; 53+/-6% versus 32+/-4% in Endo at 2 Hz). In contrast, L-768,673 (a specific I(Ks) blocker) prolonged AP less in LVH than in control. The very small I(Ks) density in Endo with LVH is consistent with the greater incidence of early afterdepolarizations induced in this region by dofetilide. CONCLUSIONS: LVH induces a decrease in I(Ks) density and increases the propensity to develop early afterdepolarizations, especially in Endo.
Xu et al. (Tue,) conducted a other in Left ventricular hypertrophy. Left ventricular hypertrophy vs. Normal rabbit left ventricular myocytes was evaluated on Slowly (I(Ks)) and rapidly (I(Kr)) activating delayed rectifier K(+) currents density and action potential repolarization. Left ventricular hypertrophy in rabbits decreased slowly activating delayed rectifier K+ current density by approximately 40% and increased the propensity for early afterdepolarizations.