93.1 Saturday, Jan. 7 Muscular Tissues of the Squid Doryteuthis pealei Express Identical Myosin Heavy Chain Isoforms SHAFFER, J.F.*; KIER, W.M.; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill email@example.com
Muscle tissue shows a remarkable diversity of contractile properties. At the molecular level, muscle contraction is generated through the enzymatic (ATPase) activity of the motor protein myosin. Variation in myosin amino acid sequences yield isoforms with a range of ATPase activity. The speed of shortening is generally proportional to myosin ATPase activity, thus, fast contracting fibers typically express a myosin isoform with high ATPase activity. Muscle fibers of the squid, however, may use an alternative mechanism to modulate contractile speed. Squid tentacle extensor muscle fibers possess ten-fold shorter thick filaments than those found in arm muscle fibers, and also contract ten times faster. The difference in thick filament lengths could explain the higher contractile speed of tentacle versus arm muscle fibers. Differences in contractile properties of the two muscle types could also be due to differences in myosin isoform ATPase activity. In order to determine if squid muscle fibers express tissue-specific myosin isoforms that could contribute to differences in contractile speed, we determined the myosin nucleotide and amino acid sequences from the tentacle, arm, fin, mantle, and funnel retractor musculature of the long-finned squid, Doryteuthis pealei. Three myosin isoforms were found in all five tissues studied, suggesting that the squid does not express tissue-specific myosin isoforms. This result supports the hypothesis that the contractile properties of squid muscle fibers are modulated by differences in ultrastructure (thick filament length) and not by myosin isoform (ATPase activity). The lack of tissue-specific myosin isoforms in the squid is unique amongst animals with muscles that display variable contractile speeds. Supported by NIGMS K12GM000678 (JFS) and NSF IOS-0951067 (WMK).