Membrane Proteins Increase with the Repeated Bout Effect.

Area of Science:

• Exercise Physiology
• Muscle Biology
• Molecular Adaptation

Background:

• The repeated bout effect (RBE) describes skeletal muscle's adaptation to injury from eccentric (ECC) contractions.
• Cellular and molecular mechanisms, especially at muscle membranes, underlying RBE are not fully understood.

Purpose of the Study:

• To investigate the response of membrane-associated proteins to the RBE.
• To identify specific proteins involved in muscle adaptation to repeated ECCs.

Main Methods:

• Mice underwent repeated in vivo ECCs over six bouts with 7-day intervals.
• Isometric torque was measured pre- and post-injury.
• Protein content of dystrophin, β-sarcoglycan, and junctophilin was analyzed using immunoblotting.

Main Results:

• Post-injury torque deficits were similar between bout 1 (36%) and bout 2 (38%) but significantly attenuated from bout 3 onwards (15-24%).
• Protein content of dystrophin, β-sarcoglycan, and junctophilin did not change after a single ECC bout.
• Repeated ECC bouts led to significant increases in dystrophin, β-sarcoglycan, and junctophilin content compared to control muscles.

Conclusions:

• The RBE demonstrates skeletal muscle's physiological plasticity.
• Repeated ECC contractions increase key membrane-associated proteins, contributing to reduced injury and strength gains.
• Accumulation of these proteins is a likely mechanism for strength adaptations during the RBE.