Physiological Fiber Types in Crayfish

                Crustacean skeletal muscles share many basic characteristics with vertebrate skeletal muscles, but exhibit greater diversity in many respects.  For example, fiber specialization (fast vs. slow, etc.) in vertebrates based on differences in myosin isoforms expressed.  A sprinter may be fast because she has a higher proportion of fast fibers, whereas a marathon runner has more slow fibers.  In crustaceans' muscles, fiber types are also specialized for diverse kinds of contraction, but the mechanisms used to generate these specializations are unique from vertebrates.  For example, in addition to different myosin isoforms being expressed, there are also significant differences in muscle sarcomere width.  These different parameters interact in complex ways to generate a number of specialized fiber types.  My thesis research focused on defining how multiple parameters interact to determine fiber types in crayfish abdominal muscles.  The crayfish extensor of the abdominal muscles contains a variety of fiber types, with several being slow or tonic, while some being fast or phasic in their chemical and biological phenotypes.  Additionally, the motor neurons, which innervate the muscles, exhibit differences in their functional features.  I used several different approaches to better understand these fiber types.  First, I recorded the resting membrane potentials in individual muscle fibers by using intracellular electrodes. My long-term goal is to determine how these different functional parameters correlate with one another to form unique fiber types.

Result of Resting membrane potential at crayfish:

            I recorded resting membrane potentials in individual muscle fibers that showed deep extensor (DEM, DEL) versus superficial extensor (SEL, SEM) at the different sections from A1 to A4/A5. The analysis revealed that the membrane potential of the deep extensor, which is responsible for the phasic motor type, was not having any significantly different from the superficial extensor, which prompts the tonic motor type. A in figure 7 that was contrary to what has been discovered in other research. Therefore, the analysis of variance (ANOVA) shows the average was ~-67 mV (Fig 7, B). However, the trajectory of the two motor types is similar to the magnitude of the average negative membrane potential which gradually increases with concentration as shown at B in figure 7, Where it illustrated the correlation between the different concentration of [K⁺] ions and resting membrane potential on the cell membrane. This was recorded from the deep extensor abdominal muscles at crayfish. According to Saladin and Miller (1998), “The negative value means that there are more negatively charged particles on the inside of the membrane than on the outside” (p. 444). Thus, this observation indicates that the membrane potential in the muscles increases with the increase [K⁺], and this confirms our expectations about the basic physiology of the membrane potential.

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