Related Experiment Video
Updated: Aug 23, 2026

Analysis of the Mitochondrial Density and Longitudinal Distribution in Rat Live-Skeletal Muscle Fibers by Confocal Microscopy
Published on: December 1, 2023
Myosin heavy chain composition of rat middle ear muscles
Hak Hyun Jung1, Seung Hoon Han, Soon Yuhl Nam
1Department of Otolaryngology-Head and Neck Surgery, University of Ulsan College of Medicine, Seoul, South Korea.
Objective:
To quantitatively analyze myosin heavy chain (MHC) mRNA composition in two rat middle ear muscles (the tensor tympani and stapedius) using competitive polymerase chain reaction (PCR).
Material And Methods:
An exogenous template, including oligonucleotide sequences specific for the seven rat MHCs (2A, 2B, 2X, 2L/EOM, embryonic, neonatal and beta-cardiac) as well as beta-actin, was constructed and used as the competitor.
Results:
The tensor tympani and stapedius contained all MHC isoforms except 2L. The tensor tympani contained approximately equal proportions of 2X (40.4% +/- 6.5%) and 2A (34.0% +/- 1.3%) MHCs, with a smaller percentage of 2B (16.6% +/- 1.5%) and neonatal (7.5% +/- 0.6%) MHCs, while beta-cardiac and embryonic MHCs were minimally expressed. The stapedius contained predominantly 2X (58.0% +/- 4.2%) and 2A (32.3% +/- 6.7%) MHCs, with a smaller percentage of 2B (7.4% +/- 0.2%) and beta-cardiac (1.9% +/- 0.1%) MHCs. Neonatal and embryonic MHCs were detected at very low levels.
Conclusion:
These results suggest that two middle ear muscles, which are mainly composed of two fast-twitching myosins (2X and 2A MHCs), contract fast and are fatigue-resistant.
More Related Videos
Related Concept Videos
Overview of Myosin Structure and Function
Actin and Myosin in Muscle Contraction
The Sarcomere
Each myosin...
The Contractile Ring
A small GTPase, RhoA, controls the function and assembly of the contractile ring. RhoA belongs to the Ras superfamily of proteins. The activation of formins by RhoA promotes...
Microscopic Anatomy of Skeletal Muscles
The muscle sarcolemma is a plasma membrane enclosing each muscle cell that conducts electrical signals called action potentials. The sarcolemma extends into the cell to form T-tubules, ensuring the neural impulses are uniformly distributed across the entire muscle...
Introduction to Actin

