Laminin

Twenty-one weeks old WT and dHT vehicle and drug treated male mice were killed by pentobarbital overdose according to the procedures approved by the Kantonal Veterinary Authority. Flexor digitorum brevis (FDB) muscles were isolated and digested with 0.2% of Collagenase type I (Clostridium hystoliticum Type I, Sigma-Aldrich) and 0.2% of Collagenase type II (Clostridium hystoliticum Type II, Worthington) in Tyrode's buffer (137 mM NaCl, 5.4 mM KCl, 0.5 mM MgCl2, 1.8 mM CaCl2, 0.1% glucose, 11.8 mM HEPES, pH 7.4 NaOH) for 45 minutes at 37 °C as described (34) . Muscles were washed with Tyrode's buffer to block the collagenase activity and gently separated from tendons using large to narrowest set of fire-polished Pasteur pipettes. Fibers obtained by this procedure remained excitable and contracted briskly when assayed experimentally. Finally, fibers were placed on laminin coated (5 µl of 1 mg/ml mouse laminin from ThermoFischer) 35 mm glass bottom dishes (MatTek corporation) for measurements of the resting [Ca 2+ ] or on ibiTreat 15µ-Slide 4 well (Ibidi) for electrically evoked Ca 2+ measurements as previously described (20) .