Increased work in cardiac trabeculae causes decreased mitochondrial NADH fluorescence followed by slow recovery.
The oxidative phosphorylation rate in isolated mitochondria is stimulated by increased [ADP], resulting in decreased [NADH]. In intact hearts, however, increased mechanical work has generally not been shown to cause an increase in [ADP]. Therefore, increased [NADH] has been suggested as an alternative for stimulating the phosphorylation rate. Such a rise in [NADH] could result from stimulation of various substrate dehydrogenases by increased intracellular [Ca2+] (e.g., during increased pacing frequency). We have monitored mitochondrial [NADH] in isolated rat ventricular trabeculae, using a novel fluorescence spectroscopy method where a native fluorescence signal was used to correct for motion artifacts. Work was controlled by increased pacing frequency and assessed using time-averaged force. At low-pacing rates (approximately 0.1 Hz), [NADH] immediately decreased during contraction and then slowly recovered (approximately 5 s) before the next contraction. At higher rates, [NADH] initially decreased by an amount related to pacing rate (i.e., work). However, during prolonged stimulation, [NADH] slowly (approximately 60 s) recovered to a new steady-state level below the initial level. We conclude that 1) during increased work, oxidative phosphorylation is not initially stimulated by increased mitochondrial [NADH]; and 2) increased pacing frequency slowly causes stimulation of NADH production.
Brandes
R
R
Loyola University Medical Center, Department of Physiology, Maywood, Illinois 60153, USA. rbrande@luc.edu
Bers
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DM
D000818:Animals; D016477:Artifacts; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D003238:Connective Tissue / Q000502:physiology*; D003486:Cyanides / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D008962:Models, Theoretical; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D051381:Rats; D011914:Rats, Inbred BN; D015203:Reproducibility of Results; D013050:Spectrometry, Fluorescence / Q000295:instrumentation / Q000379:methods; D013997:Time Factors
D003486:Cyanides; D009243:NAD; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone