FIGURE 10.

Calcium homeostasis in frataxin-depleted SH-SY5Y cells. (A) Changes in fura-2 [Ca²⁺]_cyt fluorescence intensity after addition of 25 μM veratridine. The recovery slopes for each clone after calcium entry (right, lower panel) show the difference in behavior for calcium buffering between control and frataxin-depleted clones. Traces represent means of no fewer than 100 cells from at least five experiments. (B) Changes in fura-2 [Ca²⁺]_cyt fluorescence intensity after addition of 100 μM tBuBHQ in Ca²⁺-free medium. The recovery slopes for each clone after emptying of calcium from the endoplasmic reticulum (right, lower panel) show the different behavior for calcium buffering between control and frataxin-depleted clones. The activation of SOCE with the addition of 2 mM Ca²⁺ to cells treated with 100 μM tBuBHQ in Ca²⁺-free medium is altered in frataxin-depleted cells (right, upper panel) as the activation of the process is lower than in the control cells. Traces represent means of no fewer than 100 cells from at least three experiments. (C) Changes in Calcium Green-5N fluorescence in digitonin-permeabilized cells after the addition of pulses of 4 nmol of Ca²⁺. Traces represent means of at least four experiments for each clone. The Ca²⁺ uptake velocity [(D); Student’s t-test, FXN-138.1 p = 0.0004, FXN-138.2 p = 0.0004 versus pLKO.1-NT] and capacity [(E) ;Student’s t-test, FXN-138.1 p = 0.0002, FXN-138.2 p = 0.0002 versus pLKO.1-NT] rates were calculated from the uptake slopes in (C). ***p ≤ 0.001.