Opening of mitochondrial permeability transition pore induces hypercontracture in Ca super(2+) overloaded cardiac myocytes

• Published in: Basic research in cardiology Vol. 102; no. 6; pp. 542 - 552
• Main Authors: Ruiz-Meana, M, Abellan, A, Miro-Casas, E, Garcia-Dorado, D
• Format: Journal Article
• Language: English
• Published: 01.11.2007
• ISSN: 0300-8428; 1435-1803
• DOI: 10.1007/s00395-007-0675-y

After myocardial ischemia, necrotic cell death occurs mainly during the first minutes of reperfusion through ATP-dependent hypercontracture leading to sarcolemmal rupture. Recent studies indicate that opening of a mitochondrial permeability transition pore (mPTP) is a critical event in reperfusion-induced necrosis. Objective : We investigated the hypothesis that mPTP can induce hypercontracture. Methods : Both intact and digitonin-permeabilized rat cardiac myocytes were loaded with TMRE and submitted to oxidative damage (intermittent 568 nm laser illumination) to promote mPTP, detected as mitochondrial depolarization. The effect of cytosolic Ca super(2+) overload (5 mmol/L extracellular Ca super(2+)) and ATP availability on mPTP-induced cell shortening were analyzed, and changes in cytosolic and mitochondrial Ca super(2+) were simultaneously monitored by confocal microscopy (Fluo-4 and Rhod-2). Results : In the absence of Ca super(2+) overload, induction of mPTP was consistently followed by mitochondrial depolarization and rigor shortening that, in permeabilized cells, was prevented by ATP. Exposure of intact cardiac myocytes to 5mmol/L Ca super(2+) induced an increase in cytosolic and mitochondrial Ca super(2+) content. In Ca super(2+) overloaded myocytes, induction of mPTP resulted in a further increase in cytosolic Ca super(2+) and hypercontracture (> 50% reduction in length with distortion of cell geometry) that started before depolarization involved all mitochondria within the cell and could be prevented by the mPTP inhibitor cyclosporin A. In permeabilized myocytes, mPTP could promote hypercontracture when cytosolic Ca super(2+) overload was mimicked in the presence of ATP, and was prevented when ATP was removed from the intracellular-like medium. Conclusions : mPTP opening may induce ATP-dependent hypercontracture in Ca super(2+) overloaded myocytes. This phenomenon could reconcile the apparently contradictory hypotheses of hypercontracture and mPTP opening as main determinants of necrosis during the first minutes of reperfusion.