STELLA, M.S.*; KIER, W.M.; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill: Specialization for fast contraction in the tentacle muscle of the cuttlefish, Sepia officinalis

Although muscle specialization has been studied extensively in vertebrates, less is known about the mechanisms that have evolved in invertebrate muscle that modulate muscle performance. Recent research on squid (Order Teuthida, Family Loliginidae and Ommastrephidae) arm and tentacle muscle suggests that specialization for fast contraction involved changes in the arrangement and dimensions of the myofilaments, as opposed to changes in the biochemistry of the proteins of the myofilament lattice. To begin to explore the generality of this mechanism in cephalopods, we are analyzing the transverse muscle of the tentacles of the cuttlefish, Sepia officinalis (Order Sepiida, Family Sepiidae). As in squid, the tentacles of Sepia are used in prey capture and the transverse muscle creates the extremely rapid (approximately 15 msec duration) strike. The muscle was fixed and processed for examination by transmission electron microscopy. The fibers show transverse striations with short thick filaments, and thus differ from most cephalopod muscle, which is obliquely striated and possesses long thick filaments. Since there is an inverse correlation between thick filament length and shortening velocity, these preliminary results suggest that specialization for high shortening velocity in Sepia also involved, in part, ultrastructural modifications.