An attempt was made to improve upon the methods for identifying histochemical fiber types of single fibers in the skeletal muscle.
　Single fibers were isolated from the rat lateral gastrocnemius and soleus muscles in a relaxation solution containing 5mM EGTA. Isolated single fibers were quickly frozen and serial cross-sections were cut in a cryostat. A preparation of the cross-sections in single fibers was the most important point in the present methods; it is possible to perform multiple stainings on a single fiber of short length, and similarity of the section thickness allows us to evaluate the staining intensity as a true reflection of enzyme activities.
　The cross-sections of single fibers were stained for succinate dehydrogenase and for myofibrilla ATPase after a preincubation in alkaline, acid or copper solution. For reference, the cross-sections of the freshly frozen rat plantaris muscle were stained under the same conditions as those for the single fibers.
　The staining pattern of the isolated single fibers was basically the same as that of fibers in the reference muscle except that the difference in the acid sensitivity of Type II fibers exist. This allowed us to classify the isolated single fibers into Type II A, Type II B or Type I on the basis of histochemical profiles established from the multiple stainings.
　The alteration in the acid sensitivity of myofibrilla ATPase in Type II single fibers was suggested to be brought about by an immersion of single fibers in the relaxation solution containing 5mM EGTA.

DESCENTE SPORTS SCIENCE Vol.8/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE