Simulation of cardiac work transitions, in vitro: effects of simultaneous Ca2+ and ATPase additions on isolated porcine heart mitochondria.
During increases in cardiac work there are net increases in cytosolic [Ca(2+)] and ATP hydrolysis by myofiliments and ion transport ATPases. However, it is still unclear what role Ca(2+)or the ATP hydrolysis products, ADP and Pi, have on the regulation of mitochondrial ATP production. In this study, work jumps were simulated by simultaneous additions of Ca(2+) and ATPase to porcine heart mitochondria. The net effects on the mitochondrial ATP production were monitored by simultaneously monitoring respiration (mVo2), [NADH], [ADP] and membrane potential (deltapsi) at 37 degrees C. Addition of exogenous ATPase (300 mlU.ml(-1))]ATP (3.4 mM) was used to generate a 'resting' background production of ADP. This resting metabolic rate was 200% higher than the quiescent rate while [NADH] and deltapsi were reduced. Subsequent ATPase additions (1.3IU.ml(-)) were made with varying amounts of Ca(2+)(0 to 535 nM) to simulate step increases in cardiac work. Ca(2+) additions increased mVo2 and depolarized deltapsi, and were consistent with an activation of Fo/F1)ATPase. In contrast, Ca(2+) reduced the [NADH] response to the ATPase addition, consistent with Ca(2+)-sensitive dehydrogenase activity (CaDH). The calculated free ADP response to ATPase decreased \2-fold in the presence of Ca(2+). The addition of 172nM free Ca(2+)] ATPase increased mVo2 by 300% (P<0.05, n=8) while deltapsi decreased by 14.9+/-0.1 mV without changes in [NADH] (P > or =0.05, n=8), consistent with working heart preparations. The addition of Ca(2+) and ATPase combined increased the mitochondrial ATP production rate with changes in deltapsi, NADH and [ADP], consistent with an activation of CaDH and F o /F(1)ATPase activity. These balancing effects of ATPase activity and [Ca(2+)] may explain several aspects of metabolic regulation in the heart during work transitions in vivo.
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Laboratory of Cardiac Energetics, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda 20892-1061, USA.
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Balaban
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D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008929:Mitochondria, Heart / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology*; D009243:NAD / Q000187:drug effects / Q000378:metabolism; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D013552:Swine
D009243:NAD; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium