AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 265-H274, Copyright © 1989 by American Physiological Society
Relation between phosphate metabolites and oxygen consumption of heart in vivo
L. A. Katz, J. A. Swain, M. A. Portman and R. S. Balaban
Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
The relation between induced increases in cardiac work and phosphate
metabolites was investigated in the canine heart in vivo to evaluate the
role of ATP hydrolysis products, ADP and inorganic phosphate (Pi), in the
control of myocardial oxygen consumption (MVO2). In these studies,
myocardial blood flow and oxygen consumption were simultaneously measured
with the 31P-nuclear magnetic resonance (NMR)-detected phosphate
metabolites. Three protocols were used to increase myocardial work: pacing,
epinephrine, and phenylephrine infusions. When these protocols were used,
no or only slight changes in myocardial ATP, Pi, and creatine phosphate
were observed with a greater than threefold increase in MVO2. The
calculated intracellular free Mg concentration, ADP, and pH were also only
slightly affected by these increases in work. These data indicate that a
simple model involving the feedback of cytosolic ADP and Pi to the
mitochondria regulating respiration is inadequate to explain respiratory
control in vivo. These data suggest that some other parameters or
cooperativity effects involving the phosphate metabolites must play a role
in the feedback between respiration and work in the heart in vivo.
