Inhibition of the adipose conversion of BALB/c 3T3 cells by 12-O-tetradecanoylphorbol-13-acetate: dependence on pH reduction via lactic acid production.

The effect of modifying culture pH on the adipose conversion of BALB/c 3T3 cells was studied. We have previously shown that the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) stimulates cellular lactic acid production, lowers the pH of the culture medium, and inhibits differentiation in this system. We now report that addition or organic acids such as D- or L-lactic acid or acetic acid to the culture medium mimicked the effect of TPA by lowering pH, stimulating cellular lactic acid production, and inhibiting the adipose conversion. Lowering the pH by changing the NaHCO3 concentration also inhibited differentiation. A comparison of Dulbecco's modified minimal essential medium (DMEM) vs minimal essential medium (MEM) indicated that in the former media, the rate and extent of differentiation was greater than in the MEM, and TPA neither inhibited differentiation nor stimulated lactate production. Our standard MEM medium could be made similar to DMEM with respect to the cells' response to TPA simply by raising the NaHCO3 concentration, hence, the buffering capacity, of MEM to that present in DMEM, suggesting that TPA can only inhibit differentiation in this system if it can lower culture pH via lactate production.