Objective—To investigate whether protein kinase C
(PKC) isoforms are expressed in equine skeletal muscle
and determine their distribution in various types of
fibers by use of immunofluorescence microscopy.
Animals—5 healthy adult Dutch Warmblood horses.
Procedure—In each horse, 2 biopsy specimens were
obtained from the vastus lateralis muscle.
Cryosections of equine muscle were stained with
PKC isoform (α, β1, β2, δ, ξ, or ζ)-specific polyclonal
antibodies and examined by use of a fluorescence
microscope. Homogenized muscle samples were
evaluated via western blot analysis.
Results—The PKC α, β1, β2, δ, ξ, and ζ isoforms
were localized within the fibers of equine skeletal
muscle. In addition, PKC α and β2 were detected near
or in the plasma membrane of muscle cells. For some
PKC isoforms, distribution was specific for fiber type.
Staining of cell membranes for PKC α was observed
predominantly in fibers that reacted positively with
myosin heavy chain (MHC)-IIa; PKC δ and ξ staining
were more pronounced in MHC-I-positive fibers. In
contrast, MHC-I negative fibers contained more PKC
ζ than MHC-I-positive fibers. Distribution of PKC β1
was equal among the different fiber types.
Conclusions and Clinical Relevance—Results indicated
that PKC isoforms are expressed in equine
skeletal muscle in a fiber type-specific manner.
Therefore, the involvement of PKC isoforms in signal
transduction in equine skeletal muscle might be
dependent on fiber type. ( Am J Vet Res 2004;
Procedures—Percutaneous biopsy specimens were
obtained from the vastus lateralis, pectoralis descendens,
and triceps brachii muscles. Cryosections were
stained with combinations of GLUT4 and myosin
heavy chain (MHC) specific antibodies or FAT/CD36
and MHC antibodies to assess the fiber specific
expression of GLUT4 and FAT/CD36 in equine skeletal
muscle via indirect immunofluorescent
Results—Immunofluorescent staining revealed that
GLUT4 was predominantly expressed in the cytosol
of fast type 2B fibers of equine skeletal muscle,
although several type 1 fibers in the vastus lateralis
muscle were positive for GLUT4. In all muscle fibers
examined microscopically, FAT/CD36 was strongly
expressed in the sarcolemma and capillaries. Type 1
muscle fibers also expressed small intracellular
amounts of FAT/CD36, but no intracellular FAT/CD36
expression was detected in type 2 fibers.
Conclusions and Clinical Relevance—In equine
skeletal muscle, GLUT4 and FAT/CD36 are expressed
in a fiber type selective manner. ( Am J Vet Res 2004;65:951–956)