Fig. 5: Stimulus-induced accumulation of Ca²⁺ in mitochondria in SBMA mice.

Analysis of Ca²⁺ levels in response to twitch (a, b) and tetanic (c, d) stimulation in FDB-isolated fibers of 8-week-old WT and AR100Q mice (number of myofibers derived from 3 mice/genotype: n = 65 WT and n = 66 AR100Q in a, b, and n = 58 WT and n = 53 AR100Q in c-d). e, f Analysis of Ca²⁺ levels in response to tetanic stimulation in fibers isolated from FDB of 8-week-old WT and AR100Q mice (n = 3 mice/genotype). The amount of Ca²⁺ accumulated in the cytosol during tetanic stimulation (a), calculated as the integral of the FURA_2 ratio in one second, did not show significant differences between WT and AR100Q mice. The representative ensemble average of the Ca²⁺ transients between consecutive stimuli (f) showed a faster increase as well as a faster decrease in WT than in AR100Q mice. g–i Resting and peak Ca²⁺ transients in response to caffeine (10 mM) in the cytosol (cyt, g) and mitochondria (mt, h, i) in FDB-isolated myofibers from AR100Q mice (g, h) and knock-in AR113Q mice (i) and relative control mice (cyt n ≥ 12, mt n ≥ 30 measures in myofibers derived from 3 mice/genotype/age). The graphs show the mean ± SEM; significance was tested by the two-tailed Student’s t-test. Source data are provided as a Source Data file.