Oxygen diffusion through mitochondrial membranes.
The effect of the mitochondrial membrane on the oxygen supply to the interior of mitochondria was analyzed with a cylinder model of diffusion. This estimation is based on the assumption that cytochrome a,a3 is distributed only on the inner surface of the mitochondrial inner membrane. The diffusion coefficient in the mitochondrial membrane was approximated from the fluorescently-determined viscosity of rat mitochondrial membrane. A pico-second time-resolved fluorometer at 37 degrees C gave values of 43.8 cp for intact mitochondria and 51.4 cp after phospholipase A2 treatment. Using the mean oxygen consumption rate of 10 ml O2/100 g tissue/sec in beating heart, oxygen gradients of 3.9 and 4.6 nmol was predicted across the intact and phospholipase-A2 treated mitochondrial membranes, respectively. The increased oxygen consumption during systole will yield oxygen gradients of 11.6 and 13.7 nmol. These gradients were much larger than the values estimated in a hypothetical case using the diffusion coefficient for the mitochondrial membrane of 1.5 x 10(-5) cm2/sec. The predicted oxygen gradient suggests a non-uniform distribution of oxygen in the myocardial cell and may be of importance in understanding the relationship between oxygen supply and myocardial function in hypoxia. Phospholipase A2, which is known to be activated in ischemia, destroys the microstructure of myocardial cells, seems deleterious to oxygen transport to cytochrome a,a3.
Koyama
T
T
Research Institute of Applied Electricity, Hokkaido University, Saporo, Japan.
Kinjo
M
M
Araiso
T
T
D000818:Animals; D004058:Diffusion; D003576:Electron Transport Complex IV / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008563:Membrane Lipids / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism*; D008962:Models, Theoretical; D010100:Oxygen / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D051381:Rats
D008563:Membrane Lipids; D010743:Phospholipids; D003576:Electron Transport Complex IV; D010100:Oxygen