Meeting Abstract

42.3  Wednesday, Jan. 5  Myosin isoform fiber type in the tail of the Virginia opossum (Didelphis virginiana) HAZIMIHALIS, P.J.; BUTCHER, M.T.*; Youngstown State Univ. mtbutcher@ysu.edu

Myosin heavy chain (MHC) isoforms are the primary determinants of muscle fiber contractile properties and muscle performance; therefore, the distribution of slow and fast fibers (i.e. MHC fiber types) reflect functional specializations of muscle. Muscle architecture and fiber type are well studied properties in limb muscles, however, much less is understood about these properties in axial muscles, particularly those of the tail. Opossums are an interesting lineage in this context, all have characteristic long and prehensile tails, yet species of opossum show large diversity in locomotor habit. Differences in use of the tail in locomotion suggest MHC fiber type composition may also be different. To test this hypothesis, we studied MHC isoforms and their regional distribution (proximal/middle/distal) in the tail of the Virginia opossum (Didelphis virginiana). Fiber type was determined by a combination of myosin ATPase histochemistry, immunohistochemistry, and SDS-PAGE identification of MHC isoforms. Results indicate a predominance of the fast MHC-2A isoform fiber type in the proximal and distal regions of the tail. MHC-2A fibers were found to have cross-sectional areas comparable with other fast isoform fibers, but larger than slow MHC-1 fibers. Fiber cross-sectional areas in the proximal and distal regions were also larger compared to the middle region, where the percentages of slow and fast fiber types were more evenly distributed. Interestingly, the distal region of tail contained fibers that showed incomplete staining for the fast MHC isoforms. A large composition of MHC-2A fibers and the possible presence of fast isoform hybrid fibers in the distal tail may be suggestive of a shift in MHC isoform distribution in the tail musculature of an opossum with terrestrial locomotor habits. URC#01-10