부산대학교 도서관

Although recent studies focused on the contribution of mitochondrial Ca2+ to the mechanisms ischemia-reperfusion injury, the regulation of mitochondrial Ca2+ under pathophysiological conditions remains largely unclear. By saponin-permeabilized rat myocytes, we measured mitochondrial membrane potential (ΔΠm) and mitochondrial Ca2+ concentration ([Ca2+]m) at the physiological range of cytosolic Ca2+ concentration ([Ca2+]c;300 nM) and investigated the regulation of [Ca2+]m during both normal and dissipated ΔΠm. When ΔΠm was partially depolarized by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP, 0.01–0.1 μM), there were dose-dependent decreases [Ca2+]m. When complete ΔΠm dissipation was achieved by FCCP (0.3–1 μM), [Ca2+]m remained at one-half of the control level despite no Ca2+ influx via the Ca2+ uniporter. The δΠm dissipation by FCCP accelerated calcein leakage from mitochondria in a cyclosporin (CsA)-sensitive manner, which indicates that ΔΠm dissipation opened the mitochondrial permeability transition pore (mPTP). After FCCP addition, inhibition of the mPTP by CsA caused further [Ca2+]m reduction; however, inhibition of mitochondrial Na+/Ca2+ exchange (mitoNCX) by a Na+-free solution abolished this [Ca2+]m reduction. Cytosolic Na+ concentrations that yielded one-half maximal activity levels for mitoNCX were 3.6 mM at normal ΔΠm and 7.6 mM at ΔΠm dissipation. We conclude that 1) the mitochondrial Ca2+ uniporter accumulates Ca2+ in a manner that is dependent on ΔΠm at physiological range of [Ca2+]m]c; 2) ΔΠm dissipation opens the mPTP and results in Ca2+ influx to mitochondria; and 3) although mitoNCX activity is impaired, mitoNCX extrudes Ca2+ from the matrix even after &DeltaΠm dissipation. [ABSTRACT FROM AUTHOR]