Muscle Fiber Types in Crabs: Studies on Single Identified Muscle Fibers

SYNOPSIS. Based on electrophysiological and histochemical data,four types of muscle fibers (types I, II, III and IV) can beidentified in the closer of the crab Eriphia. Although characteristicsused for typing vary among the fibers of a particular type,the combination of several parameters permits an assignment.Of particular significance for typing is the myosin ATPase activityand its stability after preincubation at different pH levels.The fiber types defined for the closer muscle can also be foundin the other leg muscles of riphia. Single, electrophysiologically identified fibers of each typewere quantitatively analyzed for several key enzymes of oxidativeand glycolytic energy metabolism (GAPDH, LDH, CS, IDH, HAD).Despite the variations found, different metabolic types canbe defined. The typing derived from biochemical studies correlateswell with that obtained electrophysiologically and histochemically.The variability of the biochemical properties, however, seemsto be considerably larger. The type I fibers can be regarded as slow oxidative, the typeII and III fibers as fast oxidative glycolytic, and the typeIV fibers as fast glycolytic.