Hypersensitivity of excitation-contraction coupling in dystrophic cardiomyocytes.
Duchenne muscular dystrophy represents a severe inherited disease of striated muscle. It is caused by a mutation of the dystrophin gene and characterized by a progressive loss of skeletal muscle function. Most patients also develop a dystrophic cardiomyopathy, resulting in dilated hypertrophy and heart failure, but the cellular mechanisms leading to the deterioration of cardiac function remain elusive. In the present study, we tested whether defective excitation-contraction (E-C) coupling contributes to impaired cardiac performance. "E-C coupling gain" was determined in cardiomyocytes from control and dystrophin-deficient mdx mice. To this end, L-type Ca2+ currents (ICaL) were measured with the whole cell patch-clamp technique, whereas Ca2+ transients were simultaneously recorded with confocal imaging of fluo-3. Initial findings indicated subtle changes of E-C coupling in mdx cells despite matched Ca2+ loading of the sarcoplasmic reticulum (SR). However, lowering the extracellular Ca2+ concentration, a maneuver used to unmask latent E-C coupling problems, was surprisingly much better tolerated by mdx myocytes, suggesting a hypersensitive E-C coupling mechanism. Challenging the SR Ca2+ release by slow elevations of the intracellular Ca2+ concentration resulted in Ca2+ oscillations after a much shorter delay in mdx cells. This is consistent with an enhanced Ca2+ sensitivity of the SR Ca2+-release channels [ryanodine receptors (RyRs)]. The hypersensitivity could be normalized by the introduction of reducing agents, indicating that the elevated cellular ROS generation in dystrophy underlies the abnormal RyR sensitivity and hypersensitive E-C coupling. Our data suggest that in dystrophin-deficient cardiomyocytes, E-C coupling is altered due to potentially arrhythmogenic changes in the Ca2+ sensitivity of redox-modified RyRs.
Department of Physiology, University of Bern, Buehlplatz 5, Bern 3012, Switzerland.
Nina D
ND
Ullrich
Mohammed
M
Fanchaouy
Konstantin
K
Gusev
Natalia
N
Shirokova
Ernst
E
Niggli
D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002311:Cardiomyopathy, Dilated / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D004195:Disease Models, Animal; D018450:Disease Progression; D016166:Free Radical Scavengers / Q000494:pharmacology; D006333:Heart Failure / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D008564:Membrane Potentials; D051379:Mice; D018101:Mice, Inbred mdx; D018613:Microscopy, Confocal; D020388:Muscular Dystrophy, Duchenne / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D017382:Reactive Oxygen Species / Q000378:metabolism; D019163:Reducing Agents / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013997:Time Factors
D020746:Calcium Channels, L-Type; D016166:Free Radical Scavengers; D017382:Reactive Oxygen Species; D019163:Reducing Agents; D019837:Ryanodine Receptor Calcium Release Channel; D012964:Sodium