Maitotoxin-induced liver cell death involving loss of cell ATP following influx of calcium

Abstract

Maitotoxin, one of the most potent marine toxins known, produced cell death in cultures of rat hepatocytes with a TD50 of 80 pm at 24 hr. The cell death, as indicated by a dose- and time-dependent leakage of lactate dehydrogenase (LDH), was also associated with the leakage of [¹⁴C]adenine nucleotides from hepatocytes prelabeled with [¹⁴C]adenine. The toxic effect of maitotoxin was completely abolished by the omission of calcium from the culture medium. The cell death induced by maitotoxin increased with increasing concentrations of calcium in the medium. Treatment of hepatocytes with low concentrations of the toxin (<0.5 ng/ml) resulted in increases in ⁴⁵Ca influx into the cells. At higher concentrations of maitotoxin (>1 ng/ml), the initial increase in ⁴⁵Ca influx was followed by the release of the ⁴⁵Ca from the cells into the medium. Since the ⁴⁵Ca release paralleled the LDH leakage, the release of calcium was due to cell death. The ⁴⁵Ca influx, [¹⁴C]adenine nucleotide leakage, and LDH leakage were effectively inhibited by verapamil, a calcium channel blocker. Maitotoxin also induced a time- and dose-dependent loss of ATP from hepatocytes, which preceded the [¹⁴C]adenine nucleotide and LDH leakage. Thus, it appears that the cell death resulting from maitotoxin treatment is caused by the elevated intracellular calcium, which in turn inhibits mitochondrial oxidative phosphorylation causing depletion of cell ATP. Loss of cell ATP may be the causative event in the maitotoxin-induced cell death.