Plasmalemma Function Is Rapidly Restored in Mdx Muscle after Eccentric Contractions

Area of Science:

• Muscle physiology
• Dystrophinopathies
• Electrophysiology

Background:

• Duchenne muscular dystrophy (DMD) is characterized by the absence of dystrophin.
• Dystrophin-deficient (mdx) mouse muscle exhibits increased susceptibility to eccentric contraction (ECC)-induced injury.
• mdx muscle demonstrates a faster recovery rate following ECC injury compared to wild-type.
• The precise mechanisms and timeline of this accelerated recovery remain unclear.

Purpose of the Study:

• To investigate the electrophysiological function of the muscle plasmalemma during and after ECC-induced injury in mdx mice.
• To determine if the loss of plasmalemmal excitability in mdx muscle is a transient phenomenon.
• To elucidate the timeline of recovery for both electrophysiological function and maximal isometric strength.

Main Methods:

• Electromyography (EMG) was employed to assess plasmalemmal electrophysiological function.
• Mice underwent implantation of stimulating electrodes on the common peroneal nerve and EMG electrodes on the tibialis anterior muscle.
• Injurious eccentric contractions (ECCs) were induced in the anterior crural muscles.
• Recovery of maximal isometric torque and M-wave root mean square (RMS) were measured post-ECC.

Main Results:

• Both mdx and wild-type mice experienced significant reductions in maximal isometric torque and M-wave RMS immediately after ECC injury.
• In mdx mice, M-wave RMS remained reduced at 2 days post-injury but recovered by 6 days, while torque recovery took up to 9 days.
• Wild-type mice showed torque recovery within 2 days, with no significant change in M-wave RMS.
• Repeated bouts of ECC contractions yielded similar results, indicating consistent injury and recovery patterns.

Conclusions:

• Functional dystrophin is essential for maintaining plasmalemmal excitation during ECC contractions.
• However, dystrophin is not required for the complete recovery of plasmalemmal electrophysiological function or maximal isometric strength.
• The transient nature of excitability loss suggests inherent compensatory mechanisms in mdx muscle recovery.