부산대학교 도서관

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