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

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.

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

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.

The Changes of Myosin Heavy Chain Isoforms after Tenotomy on Extraocular Muscle Layers of Rabbits

PURPOSE: Extraocular muscle (EOM) consists of two layers, the global and the orbital layer, which are readily distinguished by their histopathology. This study was conducted to investigate the changes of myosin heavy chain (MHC) and MHC isoforms of the global and the orbital layers of EOM after tenotomy. METHODS: Twenty four New Zealand white rabbits were used. The rectus muscles were harvested on day 3, week 1, week 2, week 3, week 4, and week 8 after EOM tenotomy. The change of MHC amount was measured using an electrophoresis. The changes of MHC isoforms were also measured quantitatively using western blot immunostaining. RESULTS: The amount of total MHC, fast MHC isoform, and slow MHC isoform decreased maximally at 1-week after EOM tenotomy and recovered at 4-week and 8-week after tenotomy. There was no significant change in the amount of the neonatal and developmental MHC isoform. CONCLUSIONS: Fast and slow MHC isoform changed mainly due to the changes in the global layer rather than in the orbital layer after EOM tenotomy.

The Change of Extraocular Muscle Layers After Tenotomy: Histologic and Immunohistochemical study

PURPOSE: Extraocular muscle (EOM) consists of two layers, orbital and global layers which are readily distinguished by their histology. This study was conducted to investigate the changes of histology, myosin heavy chain (MHC), and MHC isoforms of the global and orbital layers of EOM after tenotomy. METHODS: Forty-two New Zealand white rabbits were used. The rectus muscles were harvested at day 3, week 1, week 2, week 4, and week 8 after EOM tenotomy. EOM mass change was measured. The EOM were serially sectioned in coronal plane and stained with Masson's trichrome. The diameters of muscle fibers and cross sectional areas of two layers were measured in the middle of the muscles. Changes of MHC isoforms were also measured using immunohistochemistry. RESULTS: The EOM mass was decreased at all periods of surgery especially at day 3 and week 1, increased maximally at week 8. The diameters of EOM fibers in global layer were decreased at day 3, week 1, and week 2 after EOM tenotomy and increased maximally at week 8. The immunohistochemical stains of fast and slow MHC were weakened in the global layer at week 1 after tenotomy. CONCLUSIONS: EOM changes due to atrophy appeared at day 3, week 1, and week 2 after EOM tenotomy while EOM atrophy was recovered at week 4 and week 8 after the surgery. These changes did not appear on the EOM orbital layer but was shown in EOM global layer. These results were due to the histological and functional differences between the EOM global and orbital layers.