MODIFICATION OF TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA) PRODUCTION BY THE 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 TNF-alpha production with an EC(50) value of 35 mmol/l. The amiloride analog 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 mu M. Without HCO3- in the culture medium TNF-alpha production was inhibited by 92%. Total protein synthesis was inhibited by 85% in the absence of Na+ but did not change in the absence of bicarbonate in the culture medium, Intracellular pH (pH(i)) which increased from 6.90 in control 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 absence of HCO3- in the culture medium. In the presence of 100 mu M phloretin or DIDS the pH(i), of activated monocyte was reduced to control value, TNF-alpha production was inhibited completely and total protein synthesis was inhibited by 61%. These data suggest that (1) TNF-alpha production, as other proteins, is dependent on the pH(i) of monocytes, and (2) TNF-alpha production, in contrast to total protein, is modulated by Na+-dependent HCO3-.