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Structural responses to the photolytic release of ATP in frog muscle fibres, observed by time‐resolved X‐ray diffraction
Author(s) -
Tsaturyan Andrey K.,
Bershitsky Sergey Y.,
Burns Ronald,
He ZhenHe,
Ferenczi Michael A.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00681.x
Subject(s) - isometric exercise , biophysics , crossbridge , myosin , chemistry , actin , myosin head , crystallography , myosin light chain kinase , biochemistry , biology , physiology
1 Structural changes following the photolytic release of ATP were observed in single, permeabilised fibres of frog skeletal muscle at 5–6 °C, using time‐resolved, low‐angle X‐ray diffraction. The structural order in the fibres and their isometric function were preserved by cross‐linking 10–20 % of the myosin cross‐bridges to the thin filaments. 2 The time courses of the change in force, stiffness and in intensity of the main equatorial reflections (1,0) and (1,1), of the third myosin layer line (M3) at a reciprocal spacing of (14.5 nm) −1 on the meridian and of the first myosin‐actin layer line (LL1) were measured with 1 ms time resolution. 3 In the absence of Ca 2+ , photolytic release of ATP in muscle fibres initially in the rigor state caused the force and stiffness to decrease monotonically towards their values in relaxed muscle fibres. 4 In the presence of Ca 2+ , photolytic release of ATP resulted in an initial rapid decrease in force, followed by a slower increase to the isometric plateau. Muscle fibre stiffness decreased rapidly to ≈65 % of its value in rigor. 5 In the absence of Ca 2+ , changes on the equator, in LL1 and in M3 occurred with a time scale comparable to that of the changes in tension and stiffness. 6 In the presence of Ca 2+ , the changes on the equator and LL1 occurred simultaneously with the early phase of tension decrease. The changes in the intensity of M3 ( I M3 ) occurred on the time scale of the subsequent increase in force. The time courses of the changes in tension and I M3 were similar following the photolytic release of 0.33 or 1.1 mM ATP. However the gradual return towards the rigor state began earlier when only 0.33 mM ATP was released. 7 In the presence of Ca 2+ , the time course of changes in I M3 closely mimicked that of force development following photolytic release of ATP. This is consistent with models that propose that force development results from a change in the average orientation of cross‐bridges, although other factors, such as their redistribution, may also be involved.