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ATP-sensitive K+ channel openers prevent Ca2+ overload in rat cardiac mitochondria
E L Holmuhamedov1, L Wang, A Terzic
1Division of Cardiovascular Diseases, Department of Medicine and Pharmacology, Mayo Clinic, Mayo Foundation, Rochester, MN 55905, USA.
Abstract:
1. Mitochondrial dysfunction, secondary to excessive accumulation of Ca2+, has been implicated in cardiac injury. We here examined the action of potassium channel openers on mitochondrial Ca2+ homeostasis, as these cardioprotective ion channel modulators have recently been shown to target a mitochondrial ATP-sensitive K+ channel. 2. In isolated cardiac mitochondria, diazoxide and pinacidil decreased the rate and magnitude of Ca2+ uptake into the mitochondrial matrix with an IC50 of 65 and 128 microM, respectively. At all stages of Ca2+ uptake, the potassium channel openers depolarized the mitochondrial membrane thereby reducing Ca2+ influx through the potential-dependent mitochondrial uniporter. 3. Diazoxide and pinacidil, in a concentration-dependent manner, also activated release of Ca2+ from mitochondria. This was prevented by cyclosporin A, an inhibitor of Ca2+ release through the mitochondrial permeability transition pore. 4. Replacement of extramitochondrial K+ with mannitol abolished the effects of diazoxide and pinacidil on mitochondrial Ca2+, while the K+ ionophore valinomycin mimicked the effects of the potassium channel openers. 5. ATP and ADP, which block K+ flux through mitochondrial ATP-sensitive K+ channels, inhibited the effects of potassium channel openers, without preventing the action of valinomycin. 6. In intact cardiomyocytes, diazoxide also induced mitochondrial depolarization and decreased mitochondrial Ca2+ content. These effects were inhibited by the mitochondrial ATP-sensitive K+ channel blocker 5-hydroxydecanoic acid. 7. Thus, potassium channel openers prevent mitochondrial Ca2+ overload by reducing the driving force for Ca2+ uptake and by activating cyclosporin-sensitive Ca2+ release. In this regard, modulators of an ATP-sensitive mitochondrial K+ conductance may contribute to the maintenance of mitochondrial Ca2+ homeostasis.
Insights
Potassium channel openers protect the heart by preventing mitochondrial calcium overload. These compounds reduce calcium uptake and promote calcium release, maintaining mitochondrial calcium homeostasis.
Area of Science:
- Cardiovascular Science
- Mitochondrial Biology
- Pharmacology
Background:
- Mitochondrial dysfunction, particularly Ca2+ overload, contributes to cardiac injury.
- Cardioprotective ion channel modulators, such as potassium channel openers, may target mitochondrial ATP-sensitive K+ channels.
Purpose of the Study:
- To investigate the effects of potassium channel openers on mitochondrial Ca2+ homeostasis.
- To determine the mechanisms by which these modulators impact mitochondrial Ca2+ handling.
Main Methods:
- Experiments were conducted using isolated cardiac mitochondria and intact cardiomyocytes.
- Measurements included Ca2+ uptake and release, mitochondrial membrane potential, and the effects of specific inhibitors and ionophores.
Main Results:
- Diazoxide and pinacidil reduced mitochondrial Ca2+ uptake by depolarizing the mitochondrial membrane.
- These agents also stimulated Ca2+ release via the mitochondrial permeability transition pore, an effect inhibited by cyclosporin A.
- Effects were dependent on extramitochondrial K+ and were blocked by ATP/ADP, indicating involvement of the mitochondrial ATP-sensitive K+ channel.
Conclusions:
- Potassium channel openers prevent mitochondrial Ca2+ overload by modulating both Ca2+ influx and efflux pathways.
- These findings highlight the potential of targeting mitochondrial ATP-sensitive K+ channels for maintaining mitochondrial Ca2+ homeostasis and cardioprotection.