Meeting Abstract

P2.137  Monday, Jan. 5  Distinct Sarcomeric Protein Isoform Differences in Mammalian Fast and Slow Muscle Fibers are Associated with Muscle of Origin REISER, PJ*; BICER, S; Ohio State University; Ohio State University reiser.17@osu.edu

We previously reported the existence of a novel slow fiber type ("S1F") in limb muscles of mammalian species with relatively large adult body mass (Bicer & Reiser, J. Muscle Res. Cell Motil., 25:623-633, 2004). These fibers express slow-type myosin heavy chain (MHC-I) and slow-type myosin light chains 1 and 2 (MLC1S, MLC2S), as well as fast-type MLC1 (MLC1F) and variable levels of fast-type MLC3. Conventional slow fibers in the same species express exclusively slow-type MHC and MLC isoforms. We also reported (Reiser & Bicer, Biophys. J. 94:2301-Pos, 2008) characteristics of "F1S" fibers, common in species with low adult body mass (e.g., rodents) that, unlike conventional fast fibers which express exclusively fast-type MHC and MLC isoforms, express MLC1S, along with fast-type MHC and MLC isoforms. We now report that there are multiple subtypes of S1F fibers and of F1S fibers, that differ from each other with respect to the level of expression of specific sarcomeric protein isoforms, and these differences are consistently associated with their muscle of origin. S1F fibers isolated from dog gastrocnemius and tibialis cranialis differ from each other with respect to the relative level of S1F: ~7% and 40%, respectively, of total essential MLC (i.e., MLC1 + MLC3). F1S fibers in rat gastrocnemius and tibialis cranialis consistently differ from each other with respect to the expression of fast-type isoforms of troponin-T. These results reveal even greater complexity in patterns of sarcomeric protein isoform expression and in the distribution of fiber types in mammalian limb muscles than previously recognized. Possible influences of these differences in isoform expression on functional properties will be discussed. Supported by the National Science Foundation.