K201 modulates excitation-contraction coupling and spontaneous Ca2+ release in normal adult rabbit ventricular cardiomyocytes

Cardiovasc Res. 2007 Nov 1;76(2):236-46. doi: 10.1016/j.cardiores.2007.06.014. Epub 2007 Jun 22.


Objectives: The drug K201 (JTV-519) increases inotropy and suppresses arrhythmias in failing hearts, but the effects of K201 on normal hearts is unknown.

Methods: The effect of K201 on excitation-contraction (E-C) coupling in normal myocardium was studied by using voltage-clamp and intracellular Ca(2+) measurements in intact cells. Sarcoplasmic reticulum (SR) function was assessed using permeabilised cardiomyocytes.

Results: Acute application of <1 micromol/L K201 had no significant effect on E-C coupling. K201 at 1 micromol/L decreased Ca(2+) transient amplitude (to 83+/-7%) without affecting I(Ca,L) or the SR Ca(2+) content. At 3 micromol/L K201 caused a larger reduction of Ca(2+) transient amplitude (to 60+/-7%) with accompanying reductions in I(Ca,L) amplitude (to 66+/-8%) and SR Ca(2+) content (74+/-9%). Spontaneous SR Ca(2+) release during diastole was induced by increasing intracellular [Ca(2+)]. At 1 micromol/L K201 reduced the frequency of spontaneous Ca(2+) release. The effect of K201 on SR-mediated Ca(2+) waves and Ca(2+) sparks was examined in beta-escin-permeabilised cardiomyocytes by confocal microscopy. K201 (1 micromol/L) reduced the frequency and velocity of SR Ca(2+) waves despite no change in SR Ca(2+) content. At 3 micromol/L K201 completely abolished Ca(2+) waves and reduced the SR Ca(2+) content (to approximately 73%). K201 at 1 micromol/L reduced Ca(2+) spark amplitude and frequency. Assays specific to SR Ca(2+)-ATPase and RyR2 activity indicated that K201 inhibited both SR Ca(2+) uptake and release.

Conclusions: K201 modifies E-C coupling in normal cardiomyocytes. A dual inhibitory action on SERCA and RyR2 explains the ability of K201 to suppress spontaneous diastolic Ca(2+) release during Ca(2+) overload without significantly affecting Ca(2+) transient amplitude.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Heart Ventricles / metabolism
  • Humans
  • Myocardial Contraction / drug effects*
  • Myocytes, Cardiac / metabolism*
  • Rabbits
  • Ryanodine Receptor Calcium Release Channel / physiology
  • Sarcoplasmic Reticulum / metabolism
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism
  • Tacrolimus Binding Proteins / metabolism
  • Thiazepines / pharmacology*


  • Ryanodine Receptor Calcium Release Channel
  • Thiazepines
  • K201 compound
  • Caffeine
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • Tacrolimus Binding Proteins
  • tacrolimus binding protein 1B
  • Calcium