Premium
Myosin light chain 2 modulates MgADP‐induced contraction in rabbit skeletal and bovine cardiac skinned muscle
Author(s) -
Fujita Hideaki,
Sasaki Daisuke,
Fukuda Kenji,
Ishiwata Shin'ichi
Publication year - 2002
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 - 10.1113/jphysiol.2002.017111
Subject(s) - isometric exercise , myosin , skeletal muscle , chemistry , cardiac muscle , muscle contraction , biophysics , myofilament , biochemistry , anatomy , biology , medicine
Skinned skeletal and cardiac muscle fibres can be activated by MgADP in the presence of MgATP without Ca 2+ ; the isometric tension is developed in a sigmoidal manner with the addition of MgADP under relaxing conditions. The critical concentrations of MgADP for this MgADP‐induced contraction are about 7.5 and 2.6 m m for skeletal and cardiac muscle fibres, respectively. To investigate whether muscle regulatory proteins, myosin light chain 2 (LC 2 ) and troponin C (TnC), play a part in the MgADP‐induced contraction, these proteins were partly extracted by treatment with trans ‐1,2‐cyclohexanediamine‐ N,N,N ' ,N '‐tetraacetic acid (CDTA), a chelater of divalent cations, and the MgADP‐tension relationship was examined in rabbit psoas and bovine cardiac skinned fibres. We found that the sigmoidal MgADP‐tension relationship became hyperbolic after a partial extraction of LC 2 (about 30 %) and TnC (about 70 %). Reconstitution with LC 2 restored the sigmoidal MgADP‐tension relationship of control fibres almost fully in both skeletal and cardiac fibres, whereas reconstitution with TnC alone had no effect. Furthermore, cardiac fibres reconstituted with skeletal LC 2 exhibited an MgADP‐tension relationship intermediate between skeletal and cardiac fibres. The partial extraction of LC 2 and TnC resulted in a reduction of the inhibitory effect of inorganic phosphate (P i ) on the MgADP‐activated tension. Reconstitution with LC 2 restored the original P i ‐tension relationship, whereas reconstitution with TnC had no effect. In other words, extraction of LC 2 apparently increased the affinity of myosin for MgADP but decreased the affinity for P i . These results demonstrate that LC 2 modulates MgADP‐induced activation of actomyosin interaction.