Excitability and contractility of skeletal muscle engineered from primary cultures and cell lines

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Abstract
The purpose of this study was to compare the excitability and contractility of three-dimensional skeletal muscle constructs, termed myooids, engineered from C2C12 myoblast and 10T½ fibroblast cell lines, primary muscle cultures from adult C3H mice, and neonatal and adult Sprague-Dawley rats. Myooids were 12 mm long, with diameters of 0.1–1 mm, were excitable by transverse electrical stimulation, and contracted to produce force. After ∼30 days in culture, myooid cross-sectional area, rheobase, chronaxie, resting baseline force, twitch force, time to peak tension, one-half relaxation time, and peak isometric force were measured. Specific force was calculated by dividing peak isometric force by cross-sectional area. The specific force generated by the myooids was 2–8% of that generated by skeletal muscles of control adult rodents. Myooids engineered from C2C12-10T½ cells exhibited greater rheobase, time to peak tension, and one-half relaxation time than myooids engineered from adult rodent cultures, and myooids from C2C12-10T½ and neonatal rat cells had greater resting baseline forces than myooids from adult rodent cultures.