Intracellular PO2: a limiting factor in cell respiration

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Abstract
We previously showed that O2 consumption of isolated muscles was reversibly depressed in low PO2, without altering other measured cell functions. These findings suggested to us the possibility that some oxidative processes "run free," simply generating heat, if the P02 exceeds a certain minimal level. The present study was undertaken to see whether the oxygen available (aO2) to the cell in vivo was as low as we have found to be limiting in vitro. Microelectrodes were inserted into an isolated muscle, and alternately, into the muscle of an intact frog, rat, or rabbit. The membrane potential could often be used to establish the location of the tip of the microelectrode. The results suggest that the intracellular aO2 in vivo is lower than we found limiting in vitro, and thus probably limits O2 comsumption in vivo. This possibility permits consideration of P02 as a regulator of heat production, as well as other cell functions, as discussed in the paper.