K201 modulates excitation-contraction coupling and spontaneous Ca2+ release in normal adult rabbit ventricular cardiomyocytes.
OBJECTIVE
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.
Loughrey
C M
CM
Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, UK.
Otani
N
N
Seidler
T
T
Craig
M A
MA
Matsuda
R
R
Kaneko
N
N
Smith
G L
GL
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D022021:Tacrolimus Binding Proteins / Q000378:metabolism; D013841:Thiazepines / Q000494:pharmacology*
D019837:Ryanodine Receptor Calcium Release Channel; D013841:Thiazepines; C109183:K201 compound; D002110:Caffeine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D022021:Tacrolimus Binding Proteins; C403484:tacrolimus binding protein 1B; D002118:Calcium