N,N-dimethylformamide modulates acid extrusion from murine hepatoma cells

N,N-Dimethylformamide (DMF) affects cellular differentiation, causes hepato toxicity and gastric irritation, and may be carcinogenic. Since these proce sses involve changes in cellular pH homeostasis, we investigated the effect s of DMF on H+ extrusion and cytosolic pH (pH(i)) of mouse hepatoma cells ( Hepa 1C1C7). Extracellular pH was monitored using a silicon-based sensor sy stem (Cytosensor microphysiometer) and pH(i) was monitored by fluorescence spectrophotometry. Superfusion of cells with DMF (0.25 to 0.5 M) suppressed the extracellular acidification rate (ECAR) below baseline. Following wash out of DMF there was a rapid, concentration-dependent, prolonged overshoot of ECAR above baseline rates. Removal of extracellular Na+ or superfusion w ith amiloride abolished the overshoot in acidification rate, indicating inv olvement of Na+/H+ exchange. The overshoot was dependent on extracellular g lucose, suggesting that it arises from an increase in metabolic acid produc tion. Fluorescence measurements showed that DMF did not change pH(i). Furth ermore, DMF did not alter the rate of pH(i) recovery of cells acid loaded u sing nigericin, indicating that DMF does not directly alter Na+/H+ exchange activity in these cells. In summary, these data suggest that suppression o f acidification rate by DMF is likely due to decreased metabolic acid produ ction. Washout of DMF is then accompanied by increased glucose metabolism a nd H+ efflux via Na+/H+ exchange. It is possible that alterations in HC pro duction and transport contribute to the hepatotoxicity of DMF and its effec ts on cellular differentiation. (C) 1998 Academic Press.