Mitochondrial morphology and function varies across diaphragm muscle fiber types

High-voltage electron microscopy at 1,500 kV was used to examine mitochondrial morphology in three skeletal muscles of the rat. The soleus, deep portion of the vastus lateralis, and superficial portion of the vastus lateralis muscles were examined to represent slow-twitch oxidative, fast-twitch oxidative, glycolytic, and fast-twitch glycolytic skeletal muscle fiber types, respectively. Muscle samples were removed from six female Wistar rats. The tissues were fixed using standard electron microscopic techniques and were sectioned transversely with respect to muscle fiber orientation to approximately 0.5-micron thickness. The sections were stained on grids with uranyl acetate and Reynolds' lead citrate. Results revealed a mitochondrial reticulum in all three skeletal muscle fiber types. Stereological analyses of the electron micrographs were performed to measure volume densities and surface-to-volume ratios of mitochondria in the muscle samples. Cross-sectional volume densities of mitochondria in the soleus (15.5 +/- 1%) and deep portion of the vastus lateralis (16.1 +/- 2%) were significantly greater (P less than 0.05) than in the superficial portion of the vastus lateralis (8.7 +/- 1%). Surface-to-volume ratios of mitochondria were not significantly different between fiber types. It was concluded that the mitochondria in mammalian limb skeletal muscle are a reticulum, or network.

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Muscle fiber types and function

Current Opinion in Rheumatology ◽

10.1097/00002281-199305060-00002 ◽

1993 ◽

Vol 5 (6) ◽

pp. 695-705 ◽

Cited By ~ 32

Author(s):

Robert J. Talmadge ◽

Roland R. Roy ◽

Reggie V. Edgerton

Keyword(s):

Muscle Fiber ◽

Muscle Fiber Types ◽

Fiber Types ◽

And Function

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Differential susceptibility of diaphragm muscle fibers to neuromuscular transmission failure

Journal of Applied Physiology ◽

10.1152/jappl.1993.75.1.341 ◽

1993 ◽

Vol 75 (1) ◽

pp. 341-348 ◽

Cited By ~ 49

Author(s):

B. D. Johnson ◽

G. C. Sieck

Keyword(s):

Muscle Fiber ◽

Nerve Stimulation ◽

Neuromuscular Transmission ◽

Rank Order ◽

Diaphragm Muscle ◽

Muscle Fiber Types ◽

Fiber Types ◽

Glycogen Depletion ◽

Stimulation Rate ◽

Transmission Failure

The pattern of glycogen utilization was used to determine whether various muscle fiber types in the rat diaphragm are differentially susceptible to neuromuscular transmission failure. Muscle segments from the midcostal region were repetitively stimulated directly or via the phrenic nerve at 10 or 75 Hz. Muscle fiber types were classified histochemically as type I, IIa, or IIb. The amount of muscle fiber glycogen depletion with direct stimulation depended on stimulation rate (75 Hz > 10 Hz) and fiber type (IIb > IIa > I). However, with nerve stimulation, muscle fiber glycogen depletion did not display the same dependency on stimulation rate (10 Hz > 75 Hz), although with stimulation at 10 Hz, the same rank order of fiber depletion was observed (IIb > IIa > I). This rank order of depletion was reversed (I > IIa > IIb) during repetitive stimulation of the nerve at 75 Hz. By intermittently stimulating the muscle directly during continuous nerve stimulation, we determined that neuromuscular transmission failure contributed significantly to the force decline after 2 min of stimulation at 75 Hz but relatively little to the force decline after 2 min of stimulation at 10 Hz. A significantly greater fraction of the force decline could be attributed to neuromuscular transmission failure with repetitive bouts of stimulation at 10 Hz. We conclude that neuromuscular transmission failure causes a significant portion of the force decline after 8 min of stimulation at 10 and 75 Hz, that all diaphragm fiber types are susceptible to neuromuscular transmission failure, but that type IIb fibers are particularly susceptible at higher frequencies of stimulation.

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Long-term effects of clenbuterol on diaphragm morphology and contractile properties in emphysematous hamsters

Journal of Applied Physiology ◽

10.1152/jappl.1998.85.1.215 ◽

1998 ◽

Vol 85 (1) ◽

pp. 215-222 ◽

Cited By ~ 19

Author(s):

H. F. M. Van Der Heijden ◽

P. N. R Dekhuijzen ◽

H. Folgering ◽

L. A. Ginsel ◽

C. L. A. Van Herwaarden

Keyword(s):

Muscle Fiber ◽

Contractile Properties ◽

Diaphragm Muscle ◽

Muscle Fiber Types ◽

Type I ◽

Fiber Types ◽

Force Frequency ◽

Long Term Effects ◽

Muscle Weight

The aim of the present study was to investigate the effect of chronic long-term clenbuterol treatment (1 mg/kg subcutaneously twice a day for 12 wk) on diaphragm morphology and function in emphysematous (EH) and normal hamsters (NH). Clenbuterol increased body weight, diaphragm weight, and skeletal muscle weight in both EH and NH to a similar extent. In the diaphragm, clenbuterol significantly increased myosin heavy chain type I, IIa, and IIx muscle fiber cross-sectional areas by ∼35–55% in both EH and NH. This response to clenbuterol treatment was not significantly different between EH and NH diaphragm. In EH, twitch force (Pt), maximal tetanic force, and force-frequency curve were significantly reduced compared with NH. In EH, clenbuterol increased Pt by ∼10%, restoring Pt to NH level. A similar improvement was observed in the force-frequency characteristics. Clenbuterol did not alter contractile properties in NH. In conclusion, long-term clenbuterol treatment resulted in an increased size of all diaphragm muscle fiber types in both NH and EH. Clenbuterol completely abolished the reduced force generation induced by emphysema.

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Length-tension relationship of mammalian diaphragm muscles

Journal of Applied Physiology ◽

10.1152/jappl.1983.54.6.1681 ◽

1983 ◽

Vol 54 (6) ◽

pp. 1681-1686 ◽

Cited By ~ 72

Author(s):

K. K. McCully ◽

J. A. Faulkner

Keyword(s):

Muscle Fiber ◽

Relaxation Times ◽

Isometric Tension ◽

Diaphragm Muscle ◽

Muscle Fiber Types ◽

Fiber Types ◽

Active Tension ◽

Tension Curves ◽

Relationship Of

We tested the hypothesis that the length-tension relationship of diaphragm muscle is different from that of other skeletal muscle. Isometric contractile properties of small bundles of diaphragm muscle from rats, cats, rhesus monkeys, dogs, and pigs were measured in vitro at 37 degrees C. For diaphragm muscles from all species, twitch contraction and relaxation times and histochemical myofibrillar ATPase indicated a mixture of fast and slow muscle fiber types. By use of tetanic stimulations of 400-ms duration, isometric tension was recorded from bundles of diaphragm muscle at lengths between 50 and 130% of the muscle fiber length at which active tension was maximal (Lo). At lengths below 60–70% of Lo, tetanic tension did not reach a plateau within 400 ms. With longer stimulation durations, active tension could be recorded between 30 and 40% of Lo. The length-tension curves for bundles of fibers from the diaphragm muscle were not different among species and were consistent with results reported for intact limb muscles.

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