Acute mitochondrial toxicity of caffeine in cultured heart cells.

The cytotoxic effect of caffeine on heart cells was evaluated in primary cultures of rat heart muscle (M) and endothelioid (E) cells. The cultures were exposed to 5, 10, or 20 mM caffeine for 6, 12, or 24 hours. As an index of cytotoxicity produced by the treatments, in situ changes in mitochondrial membrane fragility were measured by a sensitive cytochemical technique. The 24 hr treatment with 20 mM caffeine was lethal to both E and M cell cultures; only the 12 hr treatment of M cell cultures with 20 mM caffeine produced significant labilization of mitochondrial membranes. The results of tests with other concentrations and durations of treatment were not statistically significant.