Determination of the respiration quotient in mammalian cell culture in bicarbonate buffered media.

The determination of the respiration quotient (RQ = CER/OUR) has not been used so far as a tool for understanding animal cell metabolism. This is due to problems in measuring the carbon dioxide evolution rate (CER) rather than the oxygen uptake rate (OUR). The determination of the CER is complicated by the use of bicarbonate in the medium. Using liquid and gas balances we have derived an equation for continuous culture to quantify the amount of CO(2) that comes from the bicarbonate in the feed. Under cell-free conditions, values predicted by this equation agree within 4% with the experimental results. In continuous culture using hybridoma cells, the CO(2) from the feed, as determined by an IR-gas analyzer, was found to represent a significant amount of the total measured CO(2) in the off-gas (50% in a suboptimal, and 30% in high-growth medium). Furthermore, the problem of CO(2) loss from the medium during medium preparation and storage was solved using both a theoretical and an experimental approach. RQ values in continuous culture were evaluated for two different growth media. Small but significant differences in RQ were measured, which were matched by differences in specific antibody rates and other metabolic quotients. In a medium with Primatone RL, an enzymatic hydrolysate of animal cell tissue that causes a more than twofold increase in cell density, the RQ was found to be 1.05, whereas in medium without Primatone RL (but containing amino acids equivalent in composition and concentration to Primatone RL) the RQ was found to be 0.97. We suggest the RQ to be a useful parameter for estimating the physiological state of cells. Its determination could be a suitable tool for both the on-line control of animal cell cultivations and the understanding of cell metabolism.