Abstract
Simultaneous determination of cell size and DNA content of hybridomas (HBβ32) revealed a direct correlation between average cell volume and progression through the cell cycle. Pseudocontinuous experiments showed that G~1~ cells, as estimated from cell size measurements, secreted monoclonal antibody at rates higher than those of cells in other stages of interphase and mitosis. Similarly, fedβbatch and batch experiments suggested that specific oxygen uptake rate (__q__O~2~) is also a function of cell cycle, being minimum for cells in G~0~ and G~1~ phase. In batch cultures, HBβ32 showed a rapid decrease in oxygen uptake rate (OUR) just prior to reaching maximum cell concentration. The OUR steadily increased from 0.01β0.05 to 0.5β0.7 mmol O~2~/L h as the cells went from the lag to the midexponential phase. The __q__O~2~ increased from 0.3 Γ 10^β10^β0.9 Γ 10^β10^ mmol O~2~/cell h at inoculation to 3.3 Γ 10^β10^β3.7 Γ 10^β10^ mmol O~2~/cell h during the early exponential phase where it remained relatively constant. Several hours before maximum cell concentration was reached, OUR and __q__O~2~ rapidly decreased to levels below those observed at inoculation. The time at which the shift in OUR and __q__O~2~ occurred and the onset of decrease in the average cell size corresponded to the time of glutamine depletion. Based on monitoring OUR onβline in batch cultures, glutamine was supplemented, resulting in increased cell concentration, extension of culture viability, and increased MAb concentration.