Figure 5.

Mitochondrial Calcium Capacity Is Reduced in PINK1 KD/KO Neurons

(A–D) Flash photolysis of permeabilized neurons loaded with Sodium Green and Rhod-5n demonstrated a flash-induced increase in [Ca²⁺]_m followed by Ca²⁺ efflux and Na⁺ influx in control cells (A). In PINK1 KD cells (B), there was no recovery of the [Ca²⁺]_m signal and reduced influx of Na⁺. Application of CGP-37157 (10 μM) to control neurons (C) inhibited the Na⁺/Ca²⁺ exchanger. Removal of Na⁺ from the medium in control neurons (D) also inhibited the Na⁺/Ca²⁺ exchanger.

(E and F) Application of 50 mM NaCl in the presence of 7 μM ruthenium red stimulated an increase in Na⁺ and decrease in Ca²⁺ in control mitochondria (E). In contrast, there was minor activation of Na⁺/Ca²⁺ exchange in PINK1 KD mitochondria (F).

(G–J) Increasing concentrations of Ca²⁺ were applied to permeabilized human neurons (G and H) or mouse neurons (I and J). Arrows indicate the final free calcium concentration to which mitochondria are exposed. Control human mitochondria (G) demonstrated a much higher Ca²⁺ capacity compared to PINK1 KD mitochondria (H). Control neurons are able to partially maintain the Δψm, until the collapse of the fluo-4 fluorescence. WT mouse neurons (I) also exhibited a higher Ca²⁺ capacity than PINK1 KO neurons (J). Note that human control neurons showed a significantly higher calcium capacity compared to mouse WT neurons.