Automated Methods for the Analysis of Skeletal Muscle Fiber Size and Metabolic Type - International Review of Cell and Molecular Biology - page 279

Padykula and colleagues ( Gauthier and Padykula, 1966; Padykula and
Herman, 1955; Stein and Padykula, 1962 ), this takes advantage of the fact
that mATPase from different skeletal muscle fiber types have different pH
stability sensitivity. For example, preincubation at pH 10.0 inactivates Type
I mATPase, whereas Type II mATPase activity is unaffected; furthermore,
Type II fibers can be further subtyped by comparing activities following pre-
incubation with pH 4.3 versus pH 4.6. In the 1970s, this method was widely
adopted, and used, for example, to distinguish three different fiber subtypes
in tibialis anterior and soleus muscles of rats ( Samaha et al., 1970 ), fiber sub-
types at different stages of development and maturation ( Brooke et al.,
1971 ), fiber subtypes expressed in intrafusal muscle fibers in cats and mon-
keys ( Ovalle and Smith, 1972 ), and to investigate changes in fiber-type com-
position associated with denervation ( Riley and Allin, 1973; Tomanek and
Lund, 1973 ). More recently, Cornachione et al. (2011) used this technique
to characterize fiber-type composition in adult and weanling rat soleus,
plantaris, EDL, and gastrocnemius muscles, whereas Glaser et al. (2010) used
it to evaluate proportions of hybrid fibers in mice after 6 weeks of
running exercise.

3.2. Fiber-typing via use of myosin subtype-specific antibodies
An underlying theme, which was confirmedwithmolecular biology methods,
is that each fiber type expresses a predominant isoform of myosin heavy chain.
Currently, four major fiber types are generally recognized in mature skeletal
muscle ( Table 7.1 ), which includes slow-type fibers (Type I) and three separate
classifications of fast-type fibers (Types IIA, IIB, and IIX). Some muscle fibers
can express two to three different myosin heavy-chain isoforms (so-called

Table 7.1 The most common fiber types in rodent and human skeletal muscle

Myosin heavy-
chain protein Fiber type Gene Comment

Type
I slow

MyHC- b MYH7 Prominent in soleus muscle, also found in

heart

Type IIA
fast

MyHC-2A MYH2 Has more oxidative capacity versus Type

IIB or IIX

Type IIB
fast

MyHC-2B MYH4 Not demonstrated in humans at the

protein level

Type IIX
fast

MyHC-2X MYH1 Type IIX and Type IIB are more

glycolytic than Type IIA