Mitochondrial oxygen consumption is synergistically inhibited by metallothionein and calcium

To determine the combined effect of metallothionein and calcium on the oxygen consumption of mitochondria.

We previously showed that mitochondrial oxygen consumption was inhibited by the intracellular acute-phase reactant, metallothionein, which is rapidly induced by nearly all stressed cells. Other investigators have demonstrated that calcium also inhibited oxygen consumption. However, the calcium concentrations used in their experiments were supraphysiologic. Our hypothesis was that metallothionein would enhance the effect of calcium.

We conducted these experiments, of a paired design, on the effects of combinations of metallothionein and calcium using mitochondria isolated from rat liver. An oxygen electrode implanted into a 600-microliter chamber with a stir bar was used to measure oxygen consumption. Various concentrations of calcium, metallothionein, and other reagents were added while oxygen consumption was being continuously recorded. Metals were removed from metallothionein by gel filtration to produce apometallothionein.

Physiological levels of metallothionein synergistically enhanced the inhibitory effect of calcium so that its action occurred at physiological concentrations. Metallothionein devoid of its metals, zinc and cadmium, had no effect on oxygen consumption.

In isolated mitochondria metallothionein inhibits ADP-initiated oxygen consumption. This effect is synergistic with the inhibitory action of calcium. These observations suggest a possible enhancement by metallothionein of the effect of fluxes in intracellular calcium in stressed cells.