The high calcium ion uptake capacity of Ehrlich ascites tumour cell mitochondria is due to inhibition of the permeability transition and phospholipase A2 activity by magnesium.

Tumour cells frequently have a high Ca2+ threshold for the mitochondrial permeability transition which occurs when a large pore in the inner membrane is opened. We studied whether this was due to the known high content of Mg2+ in Ehrlich ascites tumour cell mitochondria or to the increased expression of the protooncogene bcl-2. The latter was found not to be the case. Mg2+ potently inhibited the permeability transition and the binding of Ca2+ to the inner membrane. Also, phospholipase A2 activity was reduced by Mg2+. It is concluded that the high Ca2+ threshold is due to the high Mg2+ content in these tumour mitochondria.