Fig. 1

ASM^−/− FDB fibers show defects in excitation-contraction coupling and recovery from repeated tetanic contractions. FDB fibers were isolated from six ASM-deficient mice (ASM^−/−) and six wild type littermates (WT) and subjected to electrical field stimulation to activate Ca²⁺ release and muscle fiber contraction. a Peak Fura-2 ratios of single FDB fibers at baseline in response to stimulation across a range of physiological activation frequencies. ASM^−/− fibers showed significantly lower peak Fura-2 ratios than WT fibers at baseline. *p = 0.020 at 70 Hz, p = 0.001 at 100 Hz, p = 0.001 at 120 Hz, p = 0.008 at 150 Hz. b Average time to 50% of initial peak Fura-2 ratio during repeated 100 Hz tetanic contractions. Significantly lower values were observed in ASM^−/− fibers when compared to WT. *p = 0.011. c Peak Fura-2 ratios of single FDB fibers during measurements after 60 min of recovery from repeated tetanic contractions. No significant differences were observed at 60 min recovery in peak Fura-2 ratios between ASM^−/− and WT fibers. d Number of fibers responding to electrical stimuli at baseline and at 30 or 60 min of recovery from repeated tetanic contractions. No significant differences were observed in the total number of responsive fibers between WT or ASM^−/−