Cyclosporin and mitochondrial phospholipid degradation.

0, in Table 1 ), since mitochondrial superoxide production increases linearly with 0, tension [XI . Whereas O2 had no effect on A q development at low Ca'+, A q dissipation at high Ca? + was markedly potentiated. Thus oxidative stress acted in strict synergism with Ca? + (as observed previously with hydroperoxides [ 5 ] ) . The adverse effects of Ca" and oxidative stress were abolished by 5 mM-ATP (which was maintained by 40 mMcreatine phosphate plus 20 units of creatinephosphokinase), but lower concentrations of ATP were only partially effective. A supraphysiological concentration of ADP (maintained with 10 units of hexokinase plus 50 mwglucose) on the other hand afforded little protection. I t may be concluded that the pathophysiological free Ca? + concentration likely to be encountered after prolonged ischaemia (e.g. [Y]) , might well induce inner membrane pore opening when accompanied by high PI concentration and oxidative stress, provided that cellular ATP is substantially depleted. A prolonged period of ischaemia may be necessary, depending on the tissue, before this critical condition is attained. In heart, irreversible injury is generally associated with a decline of cellular ATP to < 40% of normoxic values [lo], which may be rapidly followed by rise in cytosolic Ca" beyond the 2 ~ U M threshold [9]. Since a high cytosolic phosphorylation potential is required for maintenance of low cytosolic Ca? + , any impairment of oxidative phosphorylation by Ca? +-induced pore opening might well initiate a vicious cycle of irreversible injury [4,6]. Table 1 also shows that even under the worst scenario with high Ca? + concentration, high P, concentration, oxidative stress and without added ATP, 0.6 pwcyclosporin allowed full development of A q . Thus cyclosporin may be of therapeutic value in halting the progression t o irreversible injury during reperfusion. Identification of the molecular target of cyclosporin may also help t o resolve the protein components involved in pore opening.