Related Experiment Video
Updated: Aug 14, 2026

Dissection of Single Skeletal Muscle Fibers for Immunofluorescent and Morphometric Analyses of Whole-Mount Neuromuscular Junctions
Published on: August 14, 2021
Contractile properties, fiber types, and myosin isoforms in fast and slow muscles of hyperactive Japanese waltzing
Gerhard Asmussen1, Ina Schmalbruch, Tomás Soukup
1Carl-Ludwig-Institute of Physiology, University Leipzig, Liebigstrasse 27, D-04103 Leipzig, Germany. asmg@medizin.uni-leipzig.de
Abstract:
This study focuses on the effects of neuromuscular hyperactivity on the contractile properties, fiber type composition, and myosin heavy chain (MHC) isoform expression of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles in Japanese waltzing mice (JWM) of the C57BL/6J-v2J strain. The same properties were studied in the homologous muscle of control CBA/J mice (CM). In comparison to CM, the JWM exhibited (i) longer activity periods, prolonged bouts of running and a higher food intake, (ii) slower twitch and tetanic contractions of both EDL and SOL muscles, decreased cold and post-tetanic potentiation of the EDL, as well as increased cold and post-tetanic depressions of the SOL. Electrophoretic analyses of MHC isoform revealed a shift toward slower isoforms in both EDL and SOL muscles of JWM as compared to the homologous muscles of CM, namely, a shift from the fastest MHCIIb to the MHCIId/x isoform in the EDL muscle and a shift from MHCIIa to MHCI in the SOL muscle. The latter also contained a higher percentage of type I fibers and displayed a higher capillary density than the SOL muscle of CM. These findings show that the inherently enhanced motor activity of the JWM leads to fiber type transitions in the direction of slower phenotypes. JWM thus represent a suitable model for studying fast-to-slow fiber transitions under the influence of spontaneous motor hyperactivity.
More Related Videos
08:12Intact Short, Intermediate, and Long Skeletal Muscle Fibers Obtained by Enzymatic Dissociation of Six Hindlimb Muscles of Mice: Beyond Flexor Digitorum Brevis
Published on: December 1, 2023
07:01Single Fiber Isolation Assay for the Assessment of Oxidative Myofiber Behavior
Published on: March 31, 2026
Related Concept Videos
Classification of Skeletal Muscle Fibers
Slow-Twitch Muscle Fibers
Slow oxidative, muscle fibers appear red due to large numbers of capillaries and high levels of...
Overview of Myosin Structure and Function
Actin and Myosin in Muscle Contraction
The Role of Actin and Myosin in Non-muscle Cells
Types of Skeletal Muscle Fibers
Fast-twitch fibers
Fast-twitch fibers, or Type II fibers, are designed for quick, powerful bursts of speed and strength. They reach peak tension within approximately 0.01 seconds following stimulation. Characterized by a large diameter and densely packed myofibrils, these fibers contain...
Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...