J Korean Ophthalmol Soc.  2009 Feb;50(2):285-289. 10.3341/jkos.2009.50.2.285.

Distribution of Myosin Heavy Chain Isoform in Human Extraocular Muscles

• Park KA
• Oh SY

• KMID: 2212064
• DOI: http://doi.org/10.3341/jkos.2009.50.2.285

Abstract

PURPOSE: To provide quantitative data on the distribution of MyHCeom and compare the proportion of myosin heavy chain (MyHC) isoforms between the central and peripheral regions of human extraocular muscles (EOMs).
METHODS
Medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscle samples were taken from three men with brain death. To examine the longitudinal distribution of myosin isoforms, the muscles were divided into central and peripheral portions of equal length. Electrophoresis and densitometry were used to quantify the distribution of MyHC isoforms.
RESULTS
Electrophoresis of whole-muscle extracts of sampled EOMs revealed four MyHC bands that were identified as MyHCI, MyHCeom, MyHCIIa, and MyHCIIx. The proportion of MyHCeom was higher in the central region, whereas the proportion of MyHCIIa was higher in the peripheral region. The relative proportions of MyHCI, MyHCeom, and MyHCIIa were not significantly different among the EOMs. There was a tendency for higher levels of MyHCIIx in the inferior rectus muscle.
CONCLUSIONS
The proportion of MyHCeom was higher in the central region of human EOMs. Further studies are needed to investigate the consequences of this distributional difference on the function of EOMs.

Keyword

Electrophoresis; Human extraocualr muscle; Myosin heavy chain isoform

MeSH Terms

Brain Death
Densitometry
Electrophoresis
Humans
Male
Muscles
Myosin Heavy Chains
Myosins
Protein Isoforms
Myosin Heavy Chains
Myosins
Protein Isoforms

Figure

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  Figure 1. SDS-PAGE of the human superior, medial, lateral and inferior rectus muscles and inferior oblique muscle (MyHCI, MyHCeom, MyHCIIa, and MyHCIIx).

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  Figure 2. Longitudinal variation in myosin heavy chain (MyHC) expression detected by high resolution SDS-PAGE. (A) Superior rectus muscle was cut into two parts as shown. (B) Myofibrils prepared from each region identified in A were analyzed by SDS-PAGE and stained with silver. The bands were identified by comparison with the migration positions in muscles of known myosin composition,5 and as described in Materials and methods. (C) Relative amounts of each MyHC were determined by scanning with visible light and densitometer.

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  Figure 3. Relative proportions of myosin heavy chain (MyHC) isoforms of extraocular muscles.

Reference

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