Novel role of extracellular carbon dioxide in lymphocyte proliferation in culture.

CO(2)/HCO(3)(-) buffering system is indispensable to maintain the pH of culture media for long-term cell culture. Now-a-days, the zwiterionic hydrogen buffer HEPES is widely used as an additional buffer in the commonly used culture media. There are reports on the successful use of HEPES-buffered media, under CO(2)/HCO(3)(-) free conditions, for long-term cell cultures. However, still CO(2)/HCO(3)(-) buffering system is widely used. We aimed at investigating the reason for this. We found that lymphocytes proliferate in response to concanavalin A only in HCO(3)(-)-buffered medium in the presence of 5% CO(2), but not in the HEPES-buffered medium in the absence of CO(2). However, lymphocyte proliferation was observed in HEPES-buffered medium in the presence of 5% CO(2) and in the absence of HCO(3)(-). On the other hand, a low level proliferation was observed in HEPES-buffered medium supplemented with HCO(3)(-) in the absence of CO(2). Supplementation of the culture medium with TCA cycle intermediates and the precursors for the salvage pathway of nucleotide synthesis did not support the lymphocyte proliferation at all. Based on these findings and other reports, we suggest that extracellular CO(2) plays a novel role in cell proliferation.