Figure 6

HtrA2 deficiency leads to ATP depletion and vulnerability to chemical ischaemia. (a–c) ATP levels were assessed indirectly using an indicator of free magnesium, Mag-Fura (5 μM). (a) shows representative traces for one WT and one HtrA2-KO midbrain neuron. Initial Mag-Fura ratio was significantly higher in HtrA2 KO traces than in WT (quantified in (b), data represented as mean±S.E.M.), indicating lower ATP levels in these cells. Inhibition of mitochondrial respiration by NaCN (1 mM) causes a slow increase in Mag-Fura ratio as ATP levels are depleted, followed by a sudden increase in Mag-Fura ratio as ATP levels are insufficient to maintain ionic homoeostasis and the cell floods with calcium. The time to onset of this bioenergetic collapse is significantly shorter in the HtrA2-KO neurons compared with WT (quantified in (c), data represented as mean±S.E.M.), indicating increased vulnerability to chemical ischaemia. * Indicates P<0.05, ** indicates P<0.01.