Abstract | OBJECTIVE: Mitochondrial [Ca2+] ([Ca2+]m) rises in parallel with cytosolic [Ca2+] ([Ca2+]c) following ATP-depletion rigor contracture induced by hypoxia in isolated cardiomyocytes. We investigated the pathways involved in the hypoxia induced changes in [Ca2+]m by using known inhibitors of mitochondrial Ca2+ transport, namely ruthenium red, an inhibitor of the Ca2+ uniporter (the normal influx route) and clonazepam, an inhibitor of Na+/Ca2+ exchange, (the normal efflux route). METHODS: [Ca2+]m was determined from indo-1/am loaded rat myocytes where the cytosolic fluorescence signal had been quenched by superfusion with Mn2+. [Ca2+]c was measured by loading myocytes with indo-1 pentapotassium salt during the isolation procedure. Cells were placed in a specially developed chamber for induction of hypoxia and reoxygenated 40 min after rigor development. RESULTS: 50% of control cells hypercontracted upon reoxygenation; this correlated with a [Ca2+]m or [Ca2+]c higher than approximately 350 nM at the end of rigor. Clonazepam completely abolished the rigor-induced rise in [Ca2+]m but not [Ca2+]c. On reoxygenation [Ca2+]m increased over the first 5 min and remained elevated whereas [Ca2+]c fell. In the presence of ruthenium red a dramatic increase in [Ca2+]m occurred 5-10 min after rigor development (the indo-1 fluorescence signal was saturated); [Ca2+]c also increased but to a lesser extent. On reoxygenation, [Ca2+]m fell rapidly even though cells hypercontracted and [Ca2+]c remained elevated. CONCLUSIONS: During hypoxia following rigor development Ca2+ uptake into mitochondria occurs largely via the Na+/Ca2+ exchanger rather than the Ca2+ uniporter whereas on reoxygenation the transporters resume their normal directionality.
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Authors | E J Griffiths, C J Ocampo, J S Savage, G A Rutter, R G Hansford, M D Stern, H S Silverman |
Journal | Cardiovascular research
(Cardiovasc Res)
Vol. 39
Issue 2
Pg. 423-33
(Aug 1998)
ISSN: 0008-6363 [Print] England |
PMID | 9798527
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Calcium Channel Blockers
- Fluorescent Dyes
- Indoles
- Sodium-Calcium Exchanger
- Ruthenium Red
- Clonazepam
- indo-1
- Oxygen
- Calcium
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Topics |
- Animals
- Calcium
(metabolism)
- Calcium Channel Blockers
(administration & dosage, pharmacology)
- Cell Size
(drug effects)
- Cells, Cultured
- Clonazepam
(administration & dosage, pharmacology)
- Cytosol
(metabolism)
- Fluorescent Dyes
- Hypoxia
(metabolism)
- Indoles
- Microscopy, Fluorescence
- Mitochondria, Heart
(drug effects, metabolism)
- Myocardium
(cytology, metabolism)
- Oxygen
(metabolism)
- Rats
- Ruthenium Red
(administration & dosage, pharmacology)
- Sodium-Calcium Exchanger
(antagonists & inhibitors)
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