DECREASING EXTRACELLULAR PH INCREASES CD13 RECEPTOR SURFACE CONTENT AND ALTERS THE METABOLISM OF HL60 CELLS CULTURED IN STIRRED-TANK BIOREACTORS

Flow cytometry and Northern blotting were used to examine the effects of extracellular pH on CD13 receptor surface content and mRNA levels o f HL60 (human promyelocytic leukemia) cells. Decreasing culture pH (7. 4, 7.2, and 7.0) increased the CD13 receptor surface content of HL60 c ells cultured at low agitation intensity (80 rpm) in 2-L bioreactors. Unlike our earlier findings on the effects of increasing agitation rat es and serum concentrations, changes in CD13 receptor content in respo nse to decreasing culture pH did not correlate with changes in CD13 mR NA levels. Decreasing culture pH also decreased the average HL60 cell size. HL60 cells cultured at pH 7.0 and 7.2 exhibited glucose consumpt ion and lactate production rates that were approximately 30-40% and 20 -30% lower, respectively, than values of cells cultured at pH 7.4.