Myosin heavy chain isoform expression in human extraocular muscles: longitudinal variation and patterns of expression in global and orbital layers.

INTRODUCTION: We investigated the distribution of myosin heavy chain (MyHC) isoforms along the length of the global and orbital layers of human extraocular muscles (EOMs).
METHODS: Whole muscle tissue extracts of human EOMs were cross-sectioned consecutively and separated into orbital and global layers. The extracts from these layers were subjected to electrophoretic analysis, followed by quantification with scanning densitometry.
RESULTS: MyHC isoforms displayed different distributions along the lengths of EOMs. In the orbital and global layers of all EOMs except for the superior oblique muscle, MyHCeom was enriched in the central regions. MyHCIIa and MyHCI were most abundant in the proximal and distal ends.
CONCLUSIONS: A variation in MyHC isoform expression was apparent along the lengths of human EOMs. These results provide a basis for understanding the molecular mechanisms underlying the functional diversity of EOMs.