T-tubule network in WT and DMD ^mdx muscle fibers. (A) Confocal images of di-8-anepps fluorescence in a WT and in a DMD^mdx fiber, at two magnifications. The white trace superimposed on each bottom image corresponds to the average fluorescence intensity profile along the region of interest enclosed within the yellow rectangle. Transmitted light images are shown on top. All scale bars correspond to 10 µm. (B) Top: Individual and corresponding mean (±SD) values for the t-tubule density index in WT and DMD^mdx fibers (n = 52 fibers from five animals in each group. P = 0.94, nested t test, 95% CI for the difference between mean values: −3.2 to 3.0). Bottom: Individual and corresponding mean (±SD) values for the average distance between adjacent t-tubules (spacing) in WT and DMD^mdx fibers (n = 48 fibers from five WT animals and n = 51 fibers from five DMD^mdx animals. P = 0.61, nested t test, 95% CI for the difference between mean values: −0.023 to 0.015). Each bar and superimposed data points correspond to data from a same animal. 95% CI, 95% confidence interval.