J Korean Ophthalmol Soc.  2009 Aug;50(8):1259-1265. 10.3341/jkos.2009.50.8.1259.

The Changes in Myosin Heavy Chain Isoforms After Extraocular Muscle Recession in Rabbits

• Sa HS
• Oh SY

• KMID: 2212546
• DOI: http://doi.org/10.3341/jkos.2009.50.8.1259

Abstract

PURPOSE
To study the changes in the amount and isoform pattern of the myosin heavy chain (MyHC) in rabbit extraocular muscle (EOM) fibers after recession. METHODS: Sixteen New Zealand white rabbits were used. Recession surgery was performed on the right superior rectus (SR) muscle by 3 mm in eight rabbits, and performed by 8 mm in other eight rabbits. The left SR muscles were left intact as the control groups. The SR muscles in both eyes were harvested from two rabbits from each recession group at 3 days and 1, 2, and 4 weeks after surgery. The changes in MyHC amount and isoform pattern were analyzed by gel electrophoresis. RESULTS: Total MyHC content decreased from 1 week after surgery in the 3-mm recessed group and from 3 days in the 8-mm group. The type IIb MyHC (MyHCIIb) plus EOM-specific MyHC (MyHCeom) showed similar proportional changes to the total MyHC at the different time points after surgery. CONCLUSIONS: The fast MyHCIIb plus the superfast MyHCeom decreased after EOM recession, and these results appear to be related to the changes in the global layer rather than in the orbital one. This suggests that the global layer might be the fast and the superfast twitch portions of rabbit EOM, which perform the fast saccades in ocular movements.

Keyword

Extraocular muscle; Global layer; Myosin heavy chain; Orbital layer; Recession

MeSH Terms

Electrophoresis
Eye
Muscles
Myosin Heavy Chains
Myosins
Orbit
Protein Isoforms
Rabbits
Saccades
Myosin Heavy Chains
Myosins
Protein Isoforms

Figure

• 

  Figure 1. SDS gel electrophoresis of rabbit ocular muscle. (A)Silver-stained electrophoretogram of myosin heavy chain (MyHC) isoforms in each two superior rectus (SR) muscles, which were harvested at 3 days, 1, 2, and 4 weeks after recession surgery, two naive SR muscles (control), two gastrocnemius muscles (GA), and two soleus muscles (Sol). The type IIb MyHC (MyHCIIb) and the EOM-specific MyHC (MyHCeom) could not be resolved in these electrophoresis bands. (B) The amount of MyHC isoforms quantified by densitometry.

• 

  Figure 2. Changes in the total myosin heavy chain (MyHC) content and in the composition of MyHC isoforms after 3-mm recession of the superior rectus (SR) muscle. (A)The total MyHC content showed no difference from the control 3 days after surgery, but decreased gradually to be 13.2 %, 24.7 % and 25.4 % lower than in the control 1 week, 2 and 4 weeks after surgery, respectively. (B) Only the proportion of MyHCIIb plus MyHCeom remained at lower level than the control at the different time points after surgery.

• 

  Figure 3. Changes in the total myosin heavy chain (MyHC) content and in the composition of MyHC isoforms after 8-mm recession of the superior rectus (SR) muscle. (A) The total MyHC content decreased to be 26.3 % lower than in the control 3 days after surgery and remained at this lower level (between 16.1 % and 32.1 %) for 4 weeks after surgery. (B) The proportions of MyHCIIa, MyHCIIx and MyHCI did not show similar change in the total MyHC after surgery. The decreasing tendency of the proportion of MyHCIIb plus MyHCeom most resembled the changes in the total MyHC content at the different time points after surgery.

Reference

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