AJP - Cell Physiology, Vol 234, Issue 3 73-C81, Copyright © 1978 by American Physiological Society
Energy relationships between cytosolic metabolism and mitochondrial respiration in rat heart
K. Nishiki, M. Erecinska and D. F. Wilson
Isolated rat heart was perfused with Langendorff's retrograde perfusion
method, while the oxygen consumption and the left ventricular pressure were
monitored continually. The steady-state contents of metabolites in the
cardiac tissue, freeze clamped under various work-load conditions, were
determined and the concentrations of free cytosolic ADP and AMP were
calculated from the near equilibrium in creatine phosphokinase and
adenylate kinase reactions. Increasing respiratory rate with increasing
load was accompanied by a fall in the cytosolic free [ATP]/[ADP][Pi] but
little change in the mitochondrial free [NAD+]/[NADH]. The free energy of
ATP hydrolysis was calculated from the concentrations of the adenine
nucleotides and compared with the values computed from the measured
turnover number for cytochrome c and redox state of the mitochondrial NAD
couple according to a mathematical model. The agreement between the two
values was good over a wide range of metabolic conditions, which provides
further support for the proposed near-equilibrium model of mitochondrial
respiration with control exerted at the cytochrome oxidase-oxygen reaction.
