Fig. 4

FDB fibers from ASM^−/− mice are defective in Ca²⁺-dependent repair of the sarcolemma after mechanical injury. FDB fibers isolated from ASM-deficient mice (ASM^−/−) and their wild type littermates (WT) were left intact or injured by one passage through a 30-gauge needle. After 5 min at 37 °C, the fibers were exposed to PI, which only enters muscle fibers that sustained a sarcolemmal damage. a Brightfield and fluorescent images of PI-stained fibers with or without needle wounding, in the presence (membrane repair permissive condition) or absence of Ca²⁺ (membrane repair non-permissive condition). b Enlarged image showing PI staining of peripheral nuclei in wounded fibers. c Quantification of PI fluorescence associated with un-contracted fibers (mean ± SE of ~ 200 fibers/animal/condition, for each experiment). The data are representative of three independent experiments. WT fibers showed the expected Ca²⁺-dependent sarcolemma repair (**p = 0.040, WT + Ca²⁺ vs. no Ca²⁺), but no significant resealing was observed in ASM^−/− fibers (p = 0.668 ASM^−/− + Ca²⁺ vs. no Ca²⁺)