Frequency dependence of Ca2+ release from the sarcoplasmic reticulum in human ventricular myocytes from end-stage heart failure.
OBJECTIVE
Human cardiac muscle from failing heart shows a decrease in active tension development and a rise in diastolic tension at stimulation frequencies above 50-60 beats/min due to both systolic and diastolic dysfunction. We have investigated underlying changes in cellular [Ca2+]i regulation.


METHODS
Single ventricular myocytes were isolated enzymatically from the explanted hearts of transplant recipients with ischemic cardiomyopathy (nhearts = 5 ncells = 15) or dilated cardiomyopathy (nhearts = 6, ncells = 19). Cells were studied during whole-cell patch clamp with fluo-3 and fura-red as [Ca2+]i indicators (36 +/- 1 degrees C).


RESULTS
In current clamp mode (action potential recording), the amplitude of Ca2+ release from the sarcoplasmic reticulum (SR) decreased at stimulation frequencies above 0.5 Hz; this decrease was more pronounced for cells from dilated cardiomyopathy. Diastolic [Ca2+]i increased at 1 and 2 Hz for both groups. Action potential duration (APD90) decreased with frequency in all cells; in addition there was a drop in plateau potential of 10 +/- 1 mV for cells from ischemic cardiomyopathy and of 13 +/- 2 mV for cells from dilated cardiomyopathy. In voltage clamp mode the L-type Ca2+ current showed reversible decrease during stimulation at 1 and 2 Hz. Recovery from inactivation during a double pulse protocol was slow (75 +/- 3% at 500 ms, 89 +/- 3% at 1000 ms) and followed the decay of the [Ca2+]i transient.


CONCLUSIONS
The negative force-frequency relation of the failing human heart is due to a decrease in Ca2+ release of the cardiac myocytes at frequencies > or = 0.5 Hz, more pronounced in dilated than in ischemic cardiomyopathy. Inhibition of ICaL at higher frequencies, at least partially related to an increase in diastolic [Ca2+]i, will contribute to this negative staircase because of a decrease in the trigger for Ca2+ release, and of decreased loading of the SR.
Sipido
K R
KR
Laboratory of Experimental Cardiology, University of Leuven, Belgium. karin.sipido@med.kuleuven.ac.be
Stankovicova
T
T
Flameng
W
W
Vanhaecke
J
J
Verdonck
F
F
D000200:Action Potentials; D000368:Aged; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D018408:Patch-Clamp Techniques; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D002118:Calcium