Effects of 4'-chlorodiazepam on cellular excitation-contraction coupling and ischaemia-reperfusion injury in rabbit heart.
OBJECTIVE
Recent evidence indicates that the activity of energy-dissipating ion channels in the mitochondria can influence the susceptibility of the heart to ischaemia-reperfusion injury. In this study, we describe the effects of 4'-chlorodiazepam (4-ClDzp), a well-known ligand of the mitochondrial benzodiazepine receptor, on the physiology of both isolated cardiomyocytes and intact hearts.


RESULTS
We used current- and voltage-clamp methods to determine the effects of 4-ClDzp on excitation-contraction coupling in isolated rabbit heart cells. At the level of the whole heart, we subjected rabbit hearts to ischaemia/reperfusion in order to determine how 4-ClDzp influenced the susceptibility to arrhythmias and contractile dysfunction. In isolated rabbit cardiomyocytes, 4-ClDzp evoked a significant reduction in the cardiac action potential that was associated with a decrease in calcium currents and peak intracellular calcium transients. In intact perfused normoxic rabbit hearts, 4-ClDzp mediated a dose-dependent negative inotropic response, consistent with the observation that 4-ClDzp was reducing calcium influx. Hearts that underwent 30 min of global ischaemia and 30 min of reperfusion were protected against reperfusion arrhythmias and post-ischaemic contractile impairment when 4-ClDzp (24 microM) was administered throughout the protocol or as a single bolus dose given at the onset of reperfusion. In contrast, hearts treated with cyclosporin-A, a classical blocker of the mitochondrial permeability transition pore, were not protected against reperfusion arrhythmias.


CONCLUSIONS
The findings indicate that the effects of 4-ClDzp on both mitochondrial and sarcolemmal ion channels contribute to protection against post-ischaemic cardiac dysfunction. Of clinical relevance, the compound is effective when given upon reperfusion, unlike other pre-conditioning agents.
Brown
David A
DA
Department of Medicine, Division of Cardiology, Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, 1059 Ross Building, Baltimore, MD 21205, USA.
Aon
Miguel A
MA
Akar
Fadi G
FG
Liu
Ting
T
Sorarrain
Nicolas
N
O'Rourke
Brian
B
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000517:prevention & control; D001570:Benzodiazepinones / Q000494:pharmacology*; D003292:Convulsants / Q000494:pharmacology*; D008024:Ligands; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D023421:Models, Animal; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011817:Rabbits; D011963:Receptors, GABA-A / Q000378:metabolism; D015427:Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control*; D018487:Ventricular Dysfunction, Left / Q000517:prevention & control
D001570:Benzodiazepinones; D003292:Convulsants; D008024:Ligands; D011963:Receptors, GABA-A; C028513:4'-chlorodiazepam