On the interactions of Ca2+ and cyclosporin A with a mitochondrial inner membrane pore: a study using cobaltammine complex inhibitors of the Ca2+ uniporter

The mitochondrial inner membrane contains a Ca(2+)-activated pore of possible relevance to the pathogenesis of ischaemia/reperfusion injury which is inhibited by the immunosuppressant cyclosporin A (CSA). The present study employs a number of novel cobaltammine complex inhibitors of the Ca2+ uniporter (mediating Ca2+ uptake) to examine whether intramitochondrial Ca2+ influences the capacity of CSA to block the pore. Using dissipation of the inner membrane potential as a means of monitoring the state of the pore, it is shown that CSA blockade is facilitated as Ca2+ uptake is restricted. Ca2+ also depresses and reverses the binding of [3H]CSA to mitochondria, but Ca2+ is ineffective when its uptake is prevented. It is concluded that a high intramitochondrial Ca2+ concentration antagonizes pore inhibition by CSA. The significance of this is discussed.