Simultaneous measurements of mitochondrial NADH and Ca(2+) during increased work in intact rat heart trabeculae.
The main goal of this study is to investigate the role of mitochondrial [Ca(2+)], [Ca(2+)](m), in the possible up-regulation of the NADH production rate during increased workload. Such up-regulation is necessary to support increased flux through the electron transport chain and increased ATP synthesis rates. Intact cardiac trabeculae were loaded with Rhod-2(AM), and [Ca(2+)](m) and mitochondrial [NADH] ([NADH](m)) were simultaneously measured during increased pacing frequency. It was found that 53% of Rhod-2 was localized in mitochondria. Increased pacing frequency caused a fast, followed by a slow rise of the Rhod-2 signal, which could be attributed to an abrupt increase in resting cytosolic [Ca(2+)], and a more gradual rise of [Ca(2+)](m), respectively. When the pacing frequency was increased from 0.25 to 2 Hz, the slow Rhod-2 component and the NADH signal increased by 18 and 11%, respectively. Based on a new calibration method, the 18% increase of the Rhod-2 signal was calculated to correspond to a 43% increase of [Ca(2+)](m). There was also a close temporal relationship between the rise (time constant approximately 25 s) and fall (time constant approximately 65 s) of [Ca(2+)](m) and [NADH](m) when the pacing frequency was increased and decreased, respectively, suggesting that increased workload and [Ca(2+)](c) cause increased [Ca(2+)](m) and consequently up-regulation of the NADH production rate.
Brandes
Rolf
R
Novasite Pharmaceuticals, San Diego, California 92121, USA. rbrandes@alumni.ucsd.edu
Bers
Donald M
DM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004579:Electron Transport; D005456:Fluorescent Dyes / Q000494:pharmacology; D006575:Heterocyclic Compounds, 3-Ring; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D051381:Rats; D012235:Rhodamines / Q000494:pharmacology; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013997:Time Factors; D015854:Up-Regulation
D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D007211:Indoles; D012235:Rhodamines; D009243:NAD; C068483:rhod-2; D008345:Manganese; C048960:indo-1; D002118:Calcium