Functional types of single muscle fibers from the depressor mandibulae muscle of R. japonica and their mechanism of excitation-contraction (E-C) coupling. I. Isolation, properties and electron microscopy of a single muscle fiber from the depressor mandibulae muscle.

An apparatus is described which collects the effluent from the center 0.7 cm of a single muscle fiber or bundle of muscle fibers. It was used to study the efflux of 45Ca from twitch muscle fibers. The efflux can be described by three time constants 18 ± 2 min, 300 ± 40 min, and 882 ± 172 min. These kinetics have been interpreted as those of a three-compartment system. The fastest is thought to be on the surface membrane of the muscle and of the T system. It contains 0.07 ± 0.03 mM Ca/liter of fiber and the Ca efflux is 0.11 ± 0.04 pM Ca/cm2. sec. The intermediate rate compartment is thought to represent the Ca in the longitudinal reticulum. It contains approximately 0.77 mM Ca/liter. Only the efflux from this compartment increases during stimulation. The most slowly exchanging compartment is poorly defined. Neither Ca-free nor Ni-Ringer solutions alter the rate of loss from the fastest exchanging compartment. Ni apparently alters the rate of loss from the slowest compartment.

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Preserved single muscle fiber specific force in facioscapulohumeral muscular dystrophy

Neurology ◽

10.1212/wnl.0000000000008977 ◽

2020 ◽

Vol 94 (11) ◽

pp. e1157-e1170 ◽

Cited By ~ 2

Author(s):

Saskia Lassche ◽

Nicol C. Voermans ◽

Robbert van der Pijl ◽

Marloes van den Berg ◽

Arend Heerschap ◽

...

Keyword(s):

Muscle Fiber ◽

Vastus Lateralis ◽

Muscle Fibers ◽

Fatty Infiltration ◽

Facioscapulohumeral Muscular Dystrophy ◽

Single Muscle ◽

Healthy Controls ◽

Specific Force ◽

Single Muscle Fiber ◽

Muscle Biopsies

ObjectiveTo investigate single muscle fiber contractile performance in muscle biopsies from patients with facioscapulohumeral muscular dystrophy (FSHD), one of the most common hereditary muscle disorders.MethodsWe collected 50 muscle biopsies (26 vastus lateralis, 24 tibialis anterior) from 14 patients with genetically confirmed FSHD and 12 healthy controls. Single muscle fibers (n = 547) were isolated for contractile measurements. Titin content and titin phosphorylation were examined in vastus lateralis muscle biopsies.ResultsSingle muscle fiber specific force was intact at saturating and physiologic calcium concentrations in all FSHD biopsies, with (FSHDFAT) and without (FSHDNORMAL) fatty infiltration, compared to healthy controls. Myofilament calcium sensitivity of force is increased in single muscle fibers obtained from FSHD muscle biopsies with increased fatty infiltration, but not in FSHD muscle biopsies without fatty infiltration (pCa50: 5.77–5.80 in healthy controls, 5.74–5.83 in FSHDNORMAL, and 5.86–5.90 in FSHDFAT single muscle fibers). Cross-bridge cycling kinetics at saturating calcium concentrations and myofilament cooperativity did not differ from healthy controls. Development of single muscle fiber passive tension was changed in all FSHD vastus lateralis and in FSHDFAT tibialis anterior, resulting in increased fiber stiffness. Titin content was increased in FSHD vastus lateralis biopsies; however, titin phosphorylation did not differ from healthy controls.ConclusionMuscle weakness in patients with FSHD is not caused by reduced specific force of individual muscle fibers, even in severely affected tissue with marked fatty infiltration of muscle tissue.

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Fiber Type and Size as Sources of Variation in Human Single Muscle Fiber Passive Elasticity

Journal of Biomechanical Engineering ◽

10.1115/1.4047423 ◽

2020 ◽

Vol 142 (8) ◽

Cited By ~ 2

Author(s):

Alex M. Noonan ◽

Derek P. Zwambag ◽

Nicole Mazara ◽

Erin Weersink ◽

Geoffrey A. Power ◽

...

Keyword(s):

Composite Materials ◽

Muscle Fiber ◽

Fiber Diameter ◽

Fiber Type ◽

Muscle Fibers ◽

Cross Sectional Area ◽

Single Muscle ◽

Sectional Area ◽

Cross Sectional ◽

Single Muscle Fiber

Abstract Studies on single muscle fiber passive material properties often report relatively large variation in elastic modulus (or normalized stiffness), and it is not clear where this variation arises. This study was designed to determine if the stiffness, normalized to both fiber cross-sectional area and length, is inherently different between types 1 and 2 muscle fibers. Vastus lateralis fibers (n = 93), from ten young men, were mechanically tested using a cumulative stretch-relaxation protocol. SDS-PAGE classified fibers as types 1 or 2. While there was a difference in normalized stiffness between fiber types (p = 0.0019), an unexpected inverse relationship was found between fiber diameter and normalized stiffness (r = −0.64; p < 0.001). As fiber type and diameter are not independent, a one-way analysis of covariance (ANCOVA) including fiber diameter as a covariate was run; this eliminated the effect of fiber type on normalized stiffness (p = 0.1935). To further explore the relationship between fiber size and elastic properties, we tested whether stiffness was linearly related to fiber cross-sectional area, as would be expected for a homogenous material. Passive stiffness was not linearly related to fiber area (p < 0.001), which can occur if single muscle fibers are better represented as composite materials. The rule of mixtures for composite materials was used to explore whether the presence of a stiff perimeter-based fiber component could explain the observed results. The model (R2 = 0.38) predicted a perimeter-based normalized stiffness of 8800 ± 2600 kPa/μm, which is within the range of basement membrane moduli reported in the literature.

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Improved single muscle fiber quality in the oldest-old

Journal of Applied Physiology ◽

10.1152/japplphysiol.00479.2016 ◽

2016 ◽

Vol 121 (4) ◽

pp. 878-884 ◽

Cited By ~ 22

Author(s):

Greg J. Grosicki ◽

Robert A. Standley ◽

Kevin A. Murach ◽

Ulrika Raue ◽

Kiril Minchev ◽

...

Keyword(s):

Muscle Fiber ◽

Fiber Quality ◽

Oldest Old ◽

Muscle Fibers ◽

Muscle Quality ◽

Vastus Lateralis Muscle ◽

Single Muscle ◽

Mhc I ◽

Single Muscle Fiber ◽

Mhc Iia

We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 yr old) enrolled in The Health, Aging, and Body Composition Study (The Health ABC Study). Vastus lateralis muscle biopsies were obtained and single muscle fiber function was determined ( n = 105) prior to myosin heavy chain (MHC) isoform identification with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-sectional area of MHC I muscle fibers (5,576 ± 333 μm2; n = 58) was 21% larger ( P < 0.05) than MHC IIa fibers (4,518 ± 386 μm2; n = 47). Normalized power (an indicator of muscle fiber quality incorporating size, strength, and speed) of MHC I and IIa muscle fibers was 2.3 ± 0.1 and 17.4 ± 0.8 W/l, respectively. Compared with previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 yr olds and similar to younger octogenarians (∼80 yr old). Normalized power of MHC IIa fibers was 63% greater than 20 yr olds and 39% greater than younger octogenarians. These comparative data suggest that power output per unit size (i.e., muscle quality) of remaining muscle fibers improves with age, a phenomenon more pronounced in MHC IIa fibers. Age-related single muscle fiber quality improvements may be a compensatory mechanism to help offset decrements in whole muscle function.

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