Electrophysiologic differences between mouse extensor digitorum longus and soleus.
Miniature end-plate potentials (MEPPs) and indirectly elicited action potentials were recorded in vivo at 37 degrees C from surface fibers of the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus (SOL) muscles of 3- to 4-month-old Bar Harbor 129 mice. The EDL MEPPs exhibited a significantly higher frequency, smaller amplitude, and shorter duration than the MEPPs of the SOL. Action potentials of EDL fibers exhibited a significantly greater amplitude and shorter duration than SOL fibers. A single stimulus elicited several action potentials from an EDL fiber but only one action potential from a SOL fiber. Fast- and slow-twitch muscle fibers can thus be identified and distinguished on the basis of these electrophysiologic parameters. There was no significant difference in resting membrane potentials between EDL and SOL fibers.
D000200:Action Potentials; D000818:Animals; D004594:Electrophysiology; D006614:Hindlimb; D051379:Mice / Q000502:physiology*; D008815:Mice, Inbred Strains; D009045:Motor Endplate / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D014034:Toes