Molecular forces involved in force generation during skeletal muscle contraction.

1996 ◽  
Vol 199 (12) ◽  
pp. 2565-2571
Author(s):  
K P Murphy ◽  
Y Zhao ◽  
M Kawai
Keyword(s):  
Skeletal Muscle ◽  
Hydrophobic Interactions ◽  
Force Generation ◽  
Muscle Fibres ◽  
Protein Chemistry ◽  
Actomyosin Interaction ◽  
Polar Interactions ◽  
Molecular Forces ◽  
Cross Bridges ◽  
Tension Transients

Recent advances in protein chemistry and the kinetic analysis of tension transients in skeletal muscle fibres have enabled us to elucidate the molecular forces involved in force generation by cross-bridges. On the basis of the temperature effect, we conclude that the elementary step that generates force is an endothermic reaction (the enthalpy change delta H degree = 124 kJ mol-1 at 15 degrees C), which accompanies a large entropy increase (delta S degree = 430JK-1 mol-1) and a reduction in the heat capacity (delta C p = -6.4kJ K-1 mol-1). Thus, it can be concluded that the force-generating step is an entropy-driven reaction. The above results suggest that hydrophobic interactions are the primary cause of force generation, and that polar interactions (hydrogen bonding and charge interactions) are involved to a lesser degree. On the basis of the thermodynamic data, we estimate that during force generation approximately 50 nm2 of surface area is involved for hydrophobic interactions and another 30 nm2 for polar interactions. These data suggest that both the actomyosin interaction and the cleft closure of the myosin head are essential for force generation.

Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfishEptatretus burgeriGirard

2002 ◽  
Vol 205 (22) ◽  
pp. 3535-3541
Author(s):  
Isao Inoue ◽  
Izuo Tsutsui ◽  
Quentin Bone
Keyword(s):  
Skeletal Muscle ◽  
Heart Muscle ◽  
Force Generation ◽  
Muscle Fibres ◽  
Fast Skeletal Muscle ◽  
K Concentration ◽  
Electrical Stimuli ◽  
Skeletal Muscle Fibres ◽  
Coupling Mechanisms ◽  
External K

SUMMARYHagfishes are regarded as the most primitive living craniates. Excitation—contraction (E—C) coupling mechanisms were studied in skeletal and caudal heart muscle fibres of the hagfish Eptatretus burgeri. In white (fast) skeletal muscle fibres from the musculus tubulatus, force generation in response to electrical stimulation was maintained in nominally Ca2+ free artificial seawater (ASW)(0Ca2+-ASW) containing 10 mmol l-1 Co2+ (a blocker of Ca2+ currents). Similarly, in red (slow) fibres from parietal muscle bathed in 0Ca2+-ASW containing 10 mmol l-1 Co2+, force generation occurred in association with K+ depolarisation when the external K+ concentration was increased to 100 mmol l-1. Therefore, external Ca2+ is not required for muscle contraction. Hence, both white and red fibres possess the function of depolarisation-induced Ca2+-release from intracellular Ca2+ stores. This function is the same as in the skeletal muscle of all other vertebrates. In caudal heart muscle fibres,twitches in response to electrical stimuli were maintained in 0Ca2+-ASW containing 30 mmol l-1 Co2+. In fibres loaded with fluo-3 bathed in 0Ca2+-ASW containing 30 mmol l-1 Co2+, an increase in the intracellular free Ca2+ level associated with K+ depolarisation was observed after the external K+ concentration was increased to 100 mmol l-1. Thus E—C coupling in the caudal heart muscle is also of the vertebrate skeletal muscle type.

Force, length, and Ca(2+)-troponin C affinity in skeletal muscle

1991 ◽  
Vol 261 (5) ◽  
pp. C787-C792 ◽  
Author(s):  
F. Fuchs ◽  
Y. P. Wang
Keyword(s):  
Skeletal Muscle ◽  
Protein Interactions ◽  
Muscle Fibers ◽  
Psoas Muscle ◽  
Troponin C ◽  
Force Generation ◽  
Fluorescence Probes ◽  
Protein Protein Interactions ◽  
Rabbit Psoas ◽  
Cross Bridges

On the basis of isotopic methods it has been found that force generation promotes increased Ca2+ binding to troponin C in cardiac muscle [P. Hofmann and F. Fuchs. Am. J. Physiol. 253 (Cell Physiol. 22): C541-C546, 1987] but not in skeletal muscle (J. Muscle Res. Cell Motil. 6: 477, 1985). However, studies with skinned rabbit psoas muscle fibers containing substituted fluorescent troponin C analogues indicate that force-generating cross bridges do promote increased Ca2+ binding in skeletal muscle (K. Guth and J. D. Potter. J. Biol. Chem. 262: 13627-13635, 1987). We have reexamined this question using a modified contraction-relaxation protocol in which Ca2+ binding to detergent-treated rabbit psoas fibers was measured either during steady-state force development or after relaxation was induced by one of two myosin ATPase inhibitors, vanadate or 2,3-butanedione monoxime. A standard double-isotope technique was used to measure Ca2+ binding. Another set of experiments was done in which force was reduced by releasing muscle fibers from sarcomere lengths of 2.4-2.6 microns to 1.5-1.7 microns, and bound Ca2+ was determined either before or after the release. No statistically significant effect of force generation or sarcomere length on Ca(2+)-troponin C affinity was observed. Thus the discrepancy remains between results obtained with isotopic and fluorescence methods. It is possible that in skinned fibers emission from fluorescence probes is more closely related to protein-protein interactions than to the amount of Ca2+ bound to troponin C.

Sign in / Sign up

Export Citation Format

Share Document