Calcium release from myofibers and muscle force generation and fatigability are normal in CD97Ko mice.

<p><b>A–D</b> Intracellular Ca²⁺ release from the SR into cytoplasm of single muscle flexor digitorum brevis (FDB) myofibers. Mean traces of the analyzed FDB fibers from adult WT and CD97Ko represent [Ca²⁺]i responses measured by Fura-2AM video microscopy. Variations in [Ca²⁺]i over time are represented by the ratio fluorescence intensities (FI) at 340 and 380 nm excitation wavelengths after dynamic background subtraction. Fibers were exposed to calcium release activators after 60 s. From 120 s till 300 s, medium without a substance was applied again. 5 mice per strain and from each mouse two to three fibers were analyzed (mean ± SEM, Mann-Whitney test). <b>A</b> Basal 340/380 fluorescence intensities (FI) ratios were unchanged in both WT and CD97ko fibers. <b>B, C</b> 100 mM KCl (B) and 30 mM caffeine (C) increased [Ca²⁺]i comparably in WT and CD97Ko fibers. <b>D</b> Application of 5 µM ionomycin as a positive control induced a fast total store [Ca²⁺]i release from the SR. <b>E, F</b> Functional analysis of skeletal muscles of CD97Ko and WT mice at the age of 2 and 4 months. Force-frequency relationship (E) and muscle fatigability, determined as percentage of decline in force over 15 s (F), were measured in soleus muscles (n = 8 mice/strain; mean ± SEM, t-test).