In:
American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 288, No. 4 ( 2005-04), p. H1820-H1828
Abstract:
Although recent studies focused on the contribution of mitochondrial Ca 2+ to the mechanisms of ischemia-reperfusion injury, the regulation of mitochondrial Ca 2+ under pathophysiological conditions remains largely unclear. By using saponin-permeabilized rat myocytes, we measured mitochondrial membrane potential (ΔΨ m ) and mitochondrial Ca 2+ concentration ([Ca 2+ ] m ) at the physiological range of cytosolic Ca 2+ concentration ([Ca 2+ ] c ; 300 nM) and investigated the regulation of [Ca 2+ ] m during both normal and dissipated ΔΨ m . When ΔΨ m was partially depolarized by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP, 0.01–0.1 μM), there were dose-dependent decreases in [Ca 2+ ] m . When complete ΔΨ m dissipation was achieved by FCCP (0.3–1 μM), [Ca 2+ ] m remained at one-half of the control level despite no Ca 2+ influx via the Ca 2+ uniporter. The ΔΨ m dissipation by FCCP accelerated calcein leakage from mitochondria in a cyclosporin A (CsA)-sensitive manner, which indicates that ΔΨ m dissipation opened the mitochondrial permeability transition pore (mPTP). After FCCP addition, inhibition of the mPTP by CsA caused further [Ca 2+ ] m reduction; however, inhibition of mitochondrial Na + /Ca 2+ exchange (mitoNCX) by a Na + -free solution abolished this [Ca 2+ ] m reduction. Cytosolic Na + concentrations that yielded one-half maximal activity levels for mitoNCX were 3.6 mM at normal ΔΨ m and 7.6 mM at ΔΨ m dissipation. We conclude that 1) the mitochondrial Ca 2+ uniporter accumulates Ca 2+ in a manner that is dependent on ΔΨ m at the physiological range of [Ca 2+ ] c ; 2) ΔΨ m dissipation opens the mPTP and results in Ca 2+ influx to mitochondria; and 3) although mitoNCX activity is impaired, mitoNCX extrudes Ca 2+ from the matrix even after ΔΨ m dissipation.
Type of Medium:
Online Resource
ISSN:
0363-6135
,
1522-1539
DOI:
10.1152/ajpheart.00589.2004
Language:
English
Publisher:
American Physiological Society
Publication Date:
2005
detail.hit.zdb_id:
1477308-9
SSG:
12
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