MODIFICATION OF TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA) PRODUCTION BYTHE NA-DEPENDENT HCO3- COTRANSPORT IN LIPOPOLYSACCHARIDE-ACTIVATED HUMAN MONOCYTES()

Tumor necrosis factor-alpha (TNF-alpha) is produced and secreted from monocytes in response to activation with lipopolysaccharide (LPS). The role of Na+ and HCO3- in the production of TNF-alpha by monocytes was investigated; it was observed that replacement of Na+ in the culture medium with sucrose or choline chloride inhibited TNF-alpha production completely. The addition of Na+ to Na+-free culture medium restored T NF-alpha production with an EC(50) value of 35 mmol/l. The amiloride a nalog 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na/H+ antiporter, inhibited TNF-alpha production with an EC(50) of 3.3 m u M. Without HCO3- in the culture medium TNF-alpha production was inhi bited by 92%. Total protein synthesis was inhibited by 85% in the abse nce of Na+ but did not change in the absence of bicarbonate in the cul ture medium, Intracellular pH (pH(i)) which increased from 6.90 in con trol monocyte to 7.40 in response to activation with LPS was abrogated to pH(i) of 6.95 in the absence of Na+ but did not change in the abse nce of HCO3- in the culture medium. In the presence of 100 mu M phlore tin or DIDS the pH(i), of activated monocyte was reduced to control va lue, TNF-alpha production was inhibited completely and total protein s ynthesis was inhibited by 61%. These data suggest that (1) TNF-alpha p roduction, as other proteins, is dependent on the pH(i) of monocytes, and (2) TNF-alpha production, in contrast to total protein, is modulat ed by Na+-dependent HCO3-.