O2 consumption and metabolic activities in resting cardiac myocytes from rainbow trout

✍ Scribed by Mortensen, B.; Gesser, H.

• Book ID: 101228302
• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 102 KB
• Volume: 283
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/(sici)1097-010x(19990501)283:6<501::aid-jez1>3.0.co;2-e

✦ Synopsis

In mammalian cardiac tissue, the O 2 consumption during mechanical rest is strikingly high. As this may relate to endothermy, the O 2 consumption of resting atrial myocytes from an ectotherm, the rainbow trout, was examined. It was 1.46 ± 0.13, 1.96 ± 0.33, 4.34 ± 0.47, and 6.37 ± 0.79 nmol min -1 mg protein -1 at 5, 10, 15, and 20°C respectively. These values are about one fourth of the maximal O 2 consumption recorded with 30 µM of the uncoupler dinitrophenol. Inhibition of mitochondrial ATP synthetase with 5 µg ml -1 oligomycin reduced resting O 2 consumption by 33 ± 9, 33 ± 1, and 24 ± 7% at 10, 15, and 20°C, respectively. Thus, only about one third of resting O 2 consumption supports ATP synthesis, whereas the rest probably represents a futile proton cycle across the mitochondrial membrane. Thus, oligomycin-insensitive O 2 consumption was not diminished by 30 µM ruthenium red, which inhibits mitochondrial Ca 2+ uptake. About one half of the 30% of the O 2 consumption coupled to ATP synthesis supports Na-K ATPase, inasmuch as 2 mM ouabain in the absence of extracellular Ca 2+ reduced O 2 consumption by about 15% at 10 and 15°C and somewhat less at 20°C. With 1.26 mM Ca 2+ , the reduction disappeared, probably due to the Na-Ca exchange. As examined at 15°C, changes in extracellular Ca 2+ , i.e., Ca 2+ load, from 0 to 1.26 and 7 mM did not affect O 2 consumption. Despite an apparent respiratory "overcapacity," lactate measurements indicate that between 10 and 20% of the ATP synthesis in the resting cells is anaerobic. Inhibition by ouabain suggests that about 30% of the lactate production supports Na + -K + -ATPase.