Abstract
We would like to study the characteristics of the mitochondrial Ca2+ dynamics in permeabilized rat ventricular myocytes. We monitored NADH, Ca2+ with Fura‐2‐FF and the mitochondrial membrane potential (ψm) with TMRE, simultaneously. We also developed a new correction method for correcting signal interference between NADH and Fura‐2‐FF. The application of 1 μM Ca2+ without cytosolic Na+ could increase intramitochondial Ca2+ upto 8 μM, which is far less than electrochemical equilibrium. The increase and loading kinetics of Ca2+ were strongly affected by the cytosolic Ca2+ concentration itself and completely blocked by RuR. The Ca2+ efflux from the mitochondria was strongly affected by the cytosolic Na+ concentration, suggested the major role of mitochondrial Na+‐Ca2+ exchange (mito‐NCX) in the Ca2+ efflux from the mitocondria. We found the cytosolic K+ was an obligatory ion to activate Ca2+ efflux through mito‐NCX. Cytosolic Cl− did not affect the mitochondrial Ca2+ dynamics. Cytosolic phosphate in addition to Ca2+ strongly inhibited Ca2+ loading and depolarized ψm. This depolarization was not blocked by CsA or 5‐HD. The increase phosphate with the increase of the cytocolic Ca2+ probably plays an important role in the degradation of mitochondrial function. This mechanism must be closely related to the post‐ischemic reperfusion injury of the heart. Supported by the grant (No. R01‐2004‐000‐10374‐0) from KOSEF
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