EXTRA AND INTRACELLULAR AMINO-ACID-CONCENTRATIONS IN CONTINUOUS CHINESE-HAMSTER OVARY CELL-CULTURE

A recombinant DNA Chinese hamster ovary (CHO) cell line that produces tissue-type plasminogen activator (tPA) was cultivated continuously in suspension with a constant dilution rate of 0.5 day with three differ ent asparagine concentrations in the feed (0.05, 2.55 and 7.55 mM). Th e up-shift in asparagine concentration caused an up-shift in asparagin e consumption [15.7 and 31.4 nmol (10(6) cells)(-1) h(-1)] and intrace llular concentration (2.19 and 18.7 mM). The up-shift was accompanied by an increased production of ammonium, glycine and alanine, and a met abolic shift whereby the cells began to produce aspartate and glutamat e, which were consumed before the shift. The tPA production was reduce d in the up-shift culture. This might be explained by ammonium inhibit ion, but alternatively by a surprising down-shift in the intracellular concentration of many amino acids, a down-shift that was not observed in the extracellular concentrations or consumption rates. For efficie nt physiological engineering of mammalian cells it is necessary to inc lude both extracellular and intracellular measurements and to consider the transport into and out of the cells.