Figure 4.

Exogenous lactic acid induces apoptosis. Lactic acid was added to culture medium to a final concentration of 16.5 mM, and the pH was adjusted to 6.8 by adding phosphoric acid. The medium was added to fresh cultures of cardiac myocytes, and the cultures were incubated under air or hypoxia as indicated. DNA fragmentation was determined as described in Methods. The initial pH in both aerobic and hypoxic cultures was 6.8; the aerobic cultures maintained this pH, but the pH of hypoxic cultures decreased further to a final pH of 5.8.