MODIFICATION OF STRUCTURE AND SYNAPTIC PHYSIOLOGY IN TRANSFORMED SHRIMP MUSCLE

1. The gross anatomy of the nerves and muscles in the pincer and snapper claws of Alpheus armillatus is described. In both claws there are three muscles: the opener muscle, the main closer muscle, Cl1, and the small closer muscle, Cl2. 2. The number of fibers in each of the two closer muscles is similar for a pair of claws removed from the same animal. However, the size of individual closer muscle fibers in the snapper is about two times greater, both in length and diameter, than in the pincer. 3. Sarcomeres in fibers of the opener muscle and the small closer muscle are similar in length for the pincer and the snapper. In contrast, sarcomeres in the main closer muscle of the pincer are shorter than those in the snapper Cl2 muscle. 4. Excitatory junctional potentials (ejp's) recorded from single pincer Clx muscle fibers at 1 Hz were always small in amplitude (≦12 mV) and facilitated poorly at 10 Hz. Snapper Cl1 ejp's ranged up to about. 30 mV in amplitude and displayed a large degree of facilitation at 10 Hz. 5. During the process of pincer transformation into a snapper claw, parallel changes occur in both the sarcomere length of Cl1 muscle fibers and the degree of ejp facilitation. © 1979 Springer-Verlag.