The lactate issue revisited: Novel feeding protocols to examine inhibitionof cell proliferation and glucose metabolism in hematopoietic cell cultures

It is well established that cell proliferation in batch (unfed) hematopoiet ic cell cultures is greatly inhibited relative to that in cultures with fee ding. What is not known, however, is the nature of this inhibition. On the basis of our observations in hematopoietic cultures that cell proliferation ceases when the lactate concentration ([lactate]) exceeds 20 mM (accompani ed by a decrease in culture pH), we investigated the effect of lactate accu mulation on cell proliferation, metabolism, and differentiation. We differ in our approach from previous efforts in that we have tried to more accurat ely recreate the manner in which lactate accumulates in culture by employin g a daily feeding protocol in which [lactate] and/or pH in the fresh medium was adjusted to match the conditions prior to feeding. We conclude that th e decrease in pH associated with lactate accumulation significantly inhibit s both cell proliferation and metabolism Although inhibition in cultures wi th high [lactate] and low pH is similar to that in unfed cultures, pH contr ol in unfed cultures does not alleviate the inhibition, indicating that oth er inhibitory factors are also present. Thus, pH control is necessary, but not sufficient, to eliminate inhibition of cell growth and metabolism in un fed hematopoietic cell cultures. We also conclude that high [lactate] and l ow pH have little effect on cell differentiation in fed cultures, although there is evidence to suggest that low pH may play a role in monocyte differ entiation in unfed cultures.