The Time Course of the Active State in Relation to Sarcomere Length and Movement Studied in Single Skeletal Muscle Fibres of the Frog

1. Intact synaptic acetylcholine receptors on freshly isolated rat skeletal-muscle fibres were characterized by their interaction with di-iodinated 125I-labelled alpha-bungarotoxin, acetylcholine and other cholinergic ligands at room temperature (22 deggrees C). 2. The time course and concentration dependence of 125I-labelled alpha-bungarotoxin association conformed to a bimolecular mechanism. In time-course experiments with different concentrations of 125I-labelled alpha-bungarotoxin (1.4–200 nM) the bimolecular-association rate constant, k + 1, was (2.27 +/- 0.49) × 10(4)M-1.S-1 (mean +/- S.D., N = 10). In concentration-dependence experiments, k + 1 was 2.10 × 10(4)M-1.S-1 and 1.74 × 10(4) M-1.S-1 with 10 and 135 min incubations respectively. In association experiments the first-order rate constant was proportional to the 125I-labelled alpha-bungarotoxin concentration. 125I-Labelled alpha-bungarotoxin dissociation was first order with a dissociation constant, k-1, less than or equal to 3 × 10(-6)S(-1) (half-life greater than or equal to 60 h.) The results indicated a single class of high-affinity toxin-binding sites at the end-plate with an equilibrium dissociation constant, Kd, equal to or less than 100 pM. The number of toxin-binding sites was (3.62 +/- 0.46) × 10(7) (mean +/- S.D., n = 22) per rat end-plate. 3. The apparent inhibitor dissociation constants, Ki, for reversible cholinergic ligands were determined by studying their effect at equilibrium on the rate of 125I-labelled alpha-bungarotoxin binding. There was heterogeneity of binding sites for cholinergic ligands, which were independent and non-interacting with antagonists. In contrast agonist affinity decreased with increasing receptor occupancy. Cholinergic ligands in excess inhibited over 90% of 125I-labelled alpha-bungarotoxin binding. 4. Cholinergic ligand binding was accompanied by an increase in entropy, which was greater for the agonist carbachol (delta So = +0.46 kJ.mol-1.K-1) than the antagonist tubocurarine (delta So = +0.26 kJ.mol-1.K-1). 5. The entropy and affinity changes that accompanied agonist binding suggested that agonists induced significant conformational changes in intact acetylcholine receptors. 6. The affinity and specificity of 125I-labelled alpha-bungarotoxin and tubocurarine binding to synaptic acetylcholine receptors from slow and fast muscle fibres were the same. 7. The study of binding only requires milligram amounts of tissue and may have application to other neurobiological studies and to the study of human neuromuscular disorders.

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Modulation of passive force in single skeletal muscle fibres

Biology Letters ◽

10.1098/rsbl.2005.0337 ◽

2005 ◽

Vol 1 (3) ◽

pp. 342-345 ◽

Cited By ~ 28

Author(s):

Dilson E Rassier ◽

Eun-Jeong Lee ◽

Walter Herzog

Keyword(s):

Skeletal Muscle ◽

Sarcomere Length ◽

Fibre Length ◽

Muscle Fibres ◽

Isometric Contractions ◽

Passive Force ◽

Length Relationship ◽

Lumbrical Muscle ◽

Single Fibres ◽

Skeletal Muscle Fibres

In this study, we investigated the effects of activation and stretch on the passive force–sarcomere length relationship in skeletal muscle. Single fibres from the lumbrical muscle of frogs were placed at varying sarcomere lengths on the descending limb of the force–sarcomere length relationship, and tetanic contractions, active stretches and passive stretches (amplitudes of ca 10% of fibre length at a speed of 40% fibre length/s) were performed. The passive forces following stretch of an activated fibre were higher than the forces measured after isometric contractions or after stretches of a passive fibre at the corresponding sarcomere length. This effect was more pronounced at increased sarcomere lengths, and the passive force–sarcomere length relationship following active stretch was shifted upwards on the force axis compared with the corresponding relationship obtained following isometric contractions or passive stretches. These results provide strong evidence for an increase in passive force that is mediated by a length-dependent combination of stretch and activation, while activation or stretch alone does not produce this effect. Based on these results and recently published findings of the effects of Ca 2+ on titin stiffness, we propose that the observed increase in passive force is caused by the molecular spring titin.

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Sarcomere length non-uniformity in relation to tetanic responses of stretched skeletal muscle fibres

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1978.0009 ◽

1978 ◽

Vol 200 (1138) ◽

pp. 109-116 ◽

Cited By ~ 20

Keyword(s):

Skeletal Muscle ◽

Thin Filament ◽

Sarcomere Length ◽

Muscle Fibres ◽

Plateau Region ◽

Constant Length ◽

Tension Response ◽

Force Velocity ◽

Skeletal Muscle Fibres ◽

Tetanic Tension

At sarcomere lengths above the plateau region of the length-tension diagram, it has been found that isometric tetanic tension is proportional to the amount of thick and thin filament overlap. This finding has been questioned recently and is reinvestigated here. Central segments of single frog skeletal muscle fibres were held at constant length during contractions at various sarcomere lengths above those associated with the plateau region. Tension records showed little or no creep, and the tetanic tensions measured at 0 and 20°C were inversely proportional to sarcomere length. These results extend and substantiate earlier findings. In contrast, when a stretched fibre had only its ends fixed during a tetanus, a different tension response was observed. The tension rise was initially very rapid but soon slowed to a gradual upward creep as stimulation was continued. This was followed by a tension decline. These tension phases were correlated with large decreases in sarcomere length at the fibre ends, while sarcomeres in the middle were extended a small amount. This tetanic tension response can be explained using the sarcomere length-tension relation and the force-velocity properties of muscle. These results strongly support the sliding filament, cross-bridge theory of muscle contraction.

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Sarcomere length dependence of the rate of tension redevelopment and submaximal tension in rat and rabbit skinned skeletal muscle fibres

The Journal of Physiology ◽

10.1111/j.1469-7793.1997.607bm.x ◽

1997 ◽

Vol 501 (3) ◽

pp. 607-621 ◽

Cited By ~ 65

Author(s):

Kerry S. McDonald ◽

Matthew R. Wolff ◽

Richard L. Moss

Keyword(s):

Skeletal Muscle ◽

Sarcomere Length ◽

Muscle Fibres ◽

Length Dependence ◽

Skeletal Muscle Fibres

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Protein Synthesis in Isolated Human Skeletal Muscle Tissue: Evaluation of an Experimental Model

Clinical Science ◽

10.1042/cs0570221 ◽

1979 ◽

Vol 57 (2) ◽

pp. 221-223 ◽

Cited By ~ 5

Author(s):

K. Lundholm ◽

T. Scherstén

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Experimental Model ◽

Muscle Tissue ◽

Time Course ◽

Human Skeletal Muscle ◽

Skeletal Muscle Tissue ◽

Muscle Fibres ◽

Skeletal Muscle Fibres

Amino acids were incorporated into soluble proteins, myosin and myoglobin at constant rates for at least 4 h on incubation of isolated human skeletal muscle fibres. The time course of incorporation of leucine into proteins not attached to ribosomes was approximately constant, suggesting a continuous termination of proteins. A comparison between estimated pool size of ribosomes and incorporation rate of leucine into proteins indicated that initiation of peptides occurred even in the absence of insulin.

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