Methodische Untersuchungen zur polarographischen Messung der Atmung und des „kritischen Sauerstoffdrucks” bei Mitochondrien und isolierten Zellen mit der membranbedeckten Platinelektrode

Summary

The respiration of cells and mitochondria of different rat tissues and of ascites tumor cells was measured with a polarographic method.

The rate of respiration (μl O₂/mg mitochondria protein×min) was controlled by the substrate, by the addition of ADP and by the temperature (25° and 37°C). By means of a membrane-covered platinum electrode no correlation was found between the rate of respiration and the$P_{{\text{O}}_{\text{2}} }$ below of which the rate of oxygen consumption decreases.

Under optimum conditions especially at saturating concentrations of ADP and substrate, the rate of respiration (measured between ∼120 and 0 Torr$P_{{\text{O}}_{\text{2}} }$) is not sufficiently constant to allow the definition of a “critical$P_{{\text{O}}_{\text{2}} }$” as the$P_{{\text{O}}_{\text{2}} }$ measured polarographically, at which the rate of respiration drops to 90% of the maximum rate. Due to the variations in the$P_{{\text{O}}_{\text{2}} }$ measurements the above “critical$P_{{\text{O}}_{\text{2}} }$” becomes strongly dependent on the method of computation used to fit the$P_{{\text{O}}_{\text{2}} }$ values measured to a straight line and to measure the rate of respiration from it. An additional difficulty is induced by the response time of the electrode which causes the$P_{{\text{O}}_{\text{2}} }$ measured to follow the real$P_{{\text{O}}_{\text{2}} }$ with a time lag large enough to significantly influence the measurements of the “critical$P_{{\text{O}}_{\text{2}} }$”.

Because of these difficulties, the so measured “critical$P_{{\text{O}}_{\text{2}} }$” is not a function of the respiratory properties of cells and mitochondria but depends largely on the measuring device.