ABSTRACT
The life-sustaining requirement for oxygen has prompted extensive investigation and analysis of the factors controlling oxygen delivery and oxygenation of the whole heart. The steady-state demand for oxygen by intact heart cells with tightly coupled mitochondria is controlled by the rate of adenosine triphosphate utilization. The fluid phase in which heart cells are suspended is in contact with a gas phase of controlled composition. Measurement of myoglobin-sensed oxygen pressure, volume averaged in the sarcoplasmic compartment of a population of isolated heart cells, demonstrates that in resting heart cells medium oxygen pressure is only 0 to 0.3 torr higher than sarcoplasmic oxygen pressure. The possibility has frequently been raised that respiring mitochondria create significant oxygen gradients inside cells, specifically around the outer mitochondrial membrane. The preparation of carefully characterized functionally intact isolated cardiac myocytes permits an analysis of the molecular mechanisms of oxygen delivery which has not been possible in the intact heart.
