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Altered pyruvate dehydrogenase control and mitochondrial free Ca2+ in hearts of cardiomyopathic hamsters
F Di Lisa1, C Z Fan, G Gambassi
1Energy Metabolism and Bioenergetics Section, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224.
Insights
Myopathic hamster hearts show reduced pyruvate dehydrogenase activity due to impaired mitochondrial calcium handling. This impacts energy production and cardiac function in these disease models.
Area of Science:
- Biochemistry
- Cardiology
- Mitochondrial Physiology
Background:
- Pyruvate dehydrogenase activity is crucial for cardiac energy metabolism.
- Myopathic hearts exhibit impaired cardiac function and altered metabolic profiles.
- Mitochondrial calcium ([Ca2+]m) regulates key metabolic enzymes.
Purpose of the Study:
- To investigate the role of pyruvate dehydrogenase interconversion in myopathic hamster hearts.
- To examine mitochondrial calcium dynamics in response to stimulation in myopathic versus healthy hearts.
- To elucidate the link between calcium handling, enzyme activity, and cardiac performance.
Main Methods:
- Comparison of pyruvate dehydrogenase activity in glucose-perfused hearts from myopathic (BIO 14.6, TO-2) and control (F1B) Syrian hamsters.
- Measurement of intramitochondrial free Ca2+ ([Ca2+]m) in isolated myocytes using fluorescence indicators.
- Application of electrical and adrenergic stimulation protocols to assess [Ca2+]m transients.
Main Results:
- Myopathic hearts displayed significantly lower active pyruvate dehydrogenase fractions and developed less pressure.
- [Ca2+]m in myopathic myocytes showed a blunted rise upon stimulation compared to controls (e.g., 348 nM vs. 830 nM at 4 Hz).
- The observed [Ca2+]m levels in myopathic hearts were below the concentration required for half-maximal pyruvate dehydrogenase activation (650 nM).
Conclusions:
- Impaired mitochondrial calcium uptake and release dynamics contribute to reduced pyruvate dehydrogenase activity in myopathic hamster hearts.
- Compromised pyruvate dehydrogenase activity and tricarboxylate cycle flux due to low [Ca2+]m likely underlie decreased oxidative phosphorylation and cardiac performance.
- This study identifies altered mitochondrial calcium handling as a key factor in the pathophysiology of these cardiac myopathies.
Abstract:
The fraction of total pyruvate dehydrogenase in the active, dephosphorylated form is much lower in the glucose-perfused isolated hearts of two myopathic strains of Syrian hamster (BIO 14.6 and TO-2) than in the hearts of healthy control animals (F1B). The myopathic hearts also develop significantly less pressure under these conditions. Experiments with isolated myocytes from the BIO 14.6 heart reveal that intramitochondrial free Ca2+ ([Ca2+]m), a positive effector of pyruvate dehydrogenase interconversion, rises much less in response to a protocol of increased frequency of electrical stimulation and adrenergic stimulation than does [Ca2+]m in cells from the healthy control animals (viz from 248 +/- 15 to 348 +/- 44 nM in BIO 14.6 vs. from 241 +/- 35 to 830 +/- 124 nM in F1B, at 4 Hz). As the concentration of Ca2+ that produces half-maximal activation of pyruvate dehydrogenase within mitochondria is 650 nM, this difference between strains is likely the mechanism of the altered enzyme interconversion. The lesser response of [Ca2+]m to electrical stimulation in the BIO 14.6 cells probably results mainly from smaller systolic transients in cytosolic free Ca2+ in response to excitation of single myocytes from the BIO 14.6 animal. Lowered values of [Ca2+]m within the range described would compromise not only pyruvate dehydrogenase activity, but also flux through the tricarboxylate cycle in the myopathic heart, owing to the sensitivity of 2-oxoglutarate dehydrogenase to Ca2+. This may explain the decreased activity of oxidative phosphorylation and performance of work in the myopathic heart.