Muscle Contractility Analysis in Mice

Muscle strength and fatigability were analyzed in EDL muscles using an ASI muscle contraction system (Aurora Scientific), equipped with a 300C-LR dual mode force transducer and a 701C stimulator. Mice were anaesthetized by intra-peritoneal injection of 100 mg/kg ketamine, 10 mg/kg xylazine, and 2 mg/kg acepromazine. EDL muscles were exposed after removing TA muscles. The proximal and distal tendons of EDL muscle were then tied using 4-0 surgical suture and EDL muscles were carefully excised and mounted between two platinum electrode plates while continuously perfused with oxygenated Ringer solution in the experimental chamber.⁴⁶ Muscle optimal length (L_o) was determined using a series of 1 Hz stimulation and set at the length that generates the maximal force. Stimulus output was set at 120% of the voltage that elicits maximal force. Muscles were first equilibrated using three 500 ms, 150 Hz tetani at 1 min intervals and then subjected to a force frequency, a single sustained high frequency tetanus (150 Hz, 2 sec) and/or a repetitive tetanic fatiguing (60 successive 50Hz, 500ms tetani) protocol. Muscle force was recorded using a Dynamic Muscle Control software and analysed using Clampfit 10.0 software. Muscle cross-sectional area and specific force were calculated as described previously⁴⁶ .