STUDY OF MAMMALIAN INTRAFUSAL MUSCLE-FIBERS USING A COMBINED HISTOCHEMICAL AND ULTRASTRUCTURAL TECHNIQUE

Abstract

The ultrastructural and histochemical properties of intrafusal muscle fibers of cat, rabbit and rat were studied to establish the number of different types fibers present and to describe their properties. Frozen sections of several hind limb muscles were used. Sections were collected for histochemically and for EM. The histochemical reactions used were ATPase following alkaline preincubation, phosphorylase and periodic acid-Schiff. Three types of intrafusal muscle fibers were found, nuclear chain fibers and 2 types of nuclear bag fibers, designated bag1 and bag2. Bag1 showed relatively low ATPase staining intensity and its sarcomeres lacked M lines in the equatorial and much of the polar regions. Bag2 showed relatively high ATPase intensity and its arcomeres possessed M lines throughout the polar regions. The properties of the nuclear chain fibers were similar to those previously described. The results are compared with previous attempts to correlate histochemical and ultrastructural properties of intrafusal muscle fibers based on indirect methods.