Redox Changes With Work in Rat Heart

Kevin E. Conley, Clyde H. Barlow, Jeffrey J. Kelly, Dawn A. Rorvik and Martin J. Kushmerick

University of Washington Medical Center, Seattle, WA 98195
Barlow Scientific, Inc., Olympia, WA 98502

Conley, K.E., Barlow, C.H., Kelly, J.J., Rorvik, D.A. and Kushmerick, M.J.  (1991)  Redox changes with work in rat heart.  Biophysical Journal  59(2 part 2), 517A.  Surface fluorescence of the heart was monitored to evaluate NADH dependent kinetic limitations to respiration during work jumps. Isolated hearts were perfused with Ringers supplemented with 15 mM glucose at 37 and 25 °C. Digital images of the heart surface fluorescence excited by a flash at 330-380 nm were obtained at 450 nm, the wavelength for maximum NADH fluorescence emission. Data were normalized to the fluorescence from pentobarbital treated hearts (100% reduction). Surface fluorescence was 77.5±1.2% [mean±SE] at 37 °C and 49.5±0.5% at 25 °C under Langendorff perfusion. Parallel 31P nuclear magnetic resonance experiments showed that ADP was not limiting to respiration since its level was above the Km for mitochondria (~25 µM) at both temperatures (37 °C: 38±11 µM; 25 °C: 35±6 µM). Significant decreases in surface fluorescence (70.2±1.7% at 37 °C and 47.2±0.6% at 25 °C) were observed with Lagendorff to working-mode trasitions where the rate-pressure product increased 3-fold. No change in ADP occurred at 37 °C (43.6±7.6 µM) but ADP increased to 56.9±3.3 µM at 25 °C. An increased surface fluorescence with a work jump is required if NADH level limits flux into the electron transport chain. Thus, NADH level did not kinetically limit respiration since surface fluorescence decreased in work jumps in rat heart.

Supported by NIH AM 36281, HL 37798, HL 43473 and U.W. Dept. of Radiology.

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