First published online April 23, 2004
Journal of Experimental Biology 207, 1875-1886 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00950
Fast fibres in a large animal: fibre types, contractile properties and myosin expression in pig skeletal muscles
Luana Toniolo1,
Marco Patruno2,
Lisa Maccatrozzo2,
Maria A. Pellegrino3,
Monica Canepari3,
Rosetta Rossi3,
Giuseppe D'Antona3,
Roberto Bottinelli3,
Carlo Reggiani1,* and
Francesco Mascarello2
1 Department of Anatomy and Physiology, University of Padova, 35131 Padova,
Italy
2 Department of Experimental Veterinary Sciences, University of Padova,
35131 Padova, Italy
3 Department of Experimental Medicine, University of Pavia, Italy
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Fig. 1. RT-PCR expression analysis of pig myosin isoforms (1, 2A, 2B, 2X) on
different muscle tissue. (A) Samples were loaded onto agarose gel in the
following order: masseter (M), longissimus dorsi (LD), semitendinosus red
portion (Sr), diaphragm (D), white semitendinosus (Sw) and duplicated masseter
(M'), longissimus dorsi (LD'), red semitendinosus (Sr'). s,
standards; 1Kb Plus DNA Ladder (Invitrogen). The brightest band (500 bp) and
bottom band (100 bp) of the molecular size markers are indicated. (B) The same
isoforms were analysed in the retractor bulbi muscle (Rb). All MHC isoforms
are expressed except for the slow isoform (type 1). The arrow indicates the
position of the amplification of the slow isoform fragment (of 573 bp, see A)
that is not expressed in this muscle. The band at 100 bp is due to primer
aspecific anealing. s, markers as in A.
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Fig. 2. Histochemistry and immunohistochemistry on a composition of masseter (m)
and longissimus dorsi (Ld) (a–c) and on a sample of red semitendinosus
(Str) (d–f). Consecutive sections were stained for mATPase with acid (pH
4.55; a) or alkali (pH 10.3; d) preincubation and with monoclonal antibodies
specific for MHC-2A (SC71; b,e) and MHC-2X (BF-35; c,f). Slow fibres (type1)
are dark with mATPase staining after acid preincubation and white after alkali
preincubation. In masseter, only type 1 and 2A are present, whereas in red
semitendinosus type 2X and 2A/X fibres are also detectable. In Ld muscle, the
conventional 2B fibre type (2*) might be either 2B or 2X or hybrids
(2A/X or 2X/B). Scale bars, 40 µm.
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Fig. 3. Histochemistry and immunohistochemistry on longissimus dorsi muscle.
Consecutive sections were stained for mATPase after acid (a) or alkali (d)
preincubation and with four monoclonal antibodies specific for MHC isoforms
(b,c,e,f). The typical organization of islets of slow fibres surrounded by
fast fibres is visible. Among fast fibres, hybrid fibres 2A/X and 2X/B are
very abundant, while only few pure 2A and 2X are present. In the deep portion
of the muscle, next to multifidus lomborum muscle, some pure 2B fibres are
detectable (indicated as B). Scale bars, 40 µm.
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Fig. 4. Electrophoretic separation of MHC isoforms in muscle samples and single
fibres. (A) Two bands (MHC-1 and MHC-2A) can be seen in masseter (M), three
bands (MHC-1 MHC-2A and MHC-2X) in diaphragm (D) and (MHC-1 MHC-2B and MHC-2X)
in red semitendinosus (Sr), white semitendinosus (Sw) and longissimus dorsi
(LD). (B) Two hybrid single fibres (2X-2B and 2X-2A) are compared with
masseter (M), diaphragm (D) and longissimus (L). (C) Five bands (three fast
MHC-2B, -2X and -2A, extraocular (Eo) and MHC-1, barely detectable) are
separated in the extraocular rectus lateralis (RL) and two bands (MHC-2X and
MHC-2B) in rectractor bulbi (RB). Three single fibres (pure 2B and hybrid
2X-2B and 2X-2A) are also shown.
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Fig. 5. Mean values of cross sectional area (CSA) (A), isometric tension
Po (B) and maximum shortening velocity
Vo (C) of the six fibre types identified in pig muscles.
Values are means ± S.E.M. ANOVA showed that (i) CSA values
of slow fibres (type 1) were significantly different from those of 2A and 2B
fibres, values of 2A fibres were significantly different from those of all
other fibre types, values of 2B fibres were significantly different from those
of all other fibre types; (ii) Po values of slow fibres
(type 1) were significantly different from those of all other fibre types
except 2B fibres and Po values of 2B fibres were
significantly different from those of all fibre types except slow fibres;
(iii) Vo values of slow fibres (type 1) were significantly
different from those of all other fibre types, Vo values
of 2A fibres were significantly different from those of all other fibre types,
Vo values of 2B fibres were significantly different from
those of all other fibre types.
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Fig. 6. Interspecies variations of Vo and
Po. (A) Relationship between maximum shortening velocity
Vo (expressed in µm h-1 s-1 for
correct comparison among species) and body size. A regression line for slow
fibres was obtained by fitting the experimental data with the scaling equation
y=ax-b; the parameters were a=3.309±0.614
and b=0.192±0.013. (B) Values of isometric tension
Po measured in various fibre types in five animal species.
Statistically significant differences were found for slow fibres (mouse and
pig different from all other species) and for 2B fibres (pig different from
all other species). Data for mouse, rat, rabbit and man from Pellegrino et al.
(2003 ).
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© The Company of Biologists Ltd 2004
