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Mechanism of action of endothelin in rat cardiac muscle: cross‐bridge kinetics and myosin light chain phosphorylation
Author(s) -
Rossmanith Gunther H.,
Hoh Joseph F. Y.,
Turnbull Lynne,
Ludowyke Russell I.
Publication year - 1997
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.1469-7793.1997.217bc.x
Subject(s) - isometric exercise , chemistry , myosin light chain kinase , myosin , medicine , contracture , biophysics , endocrinology , kinetics , skeletal muscle , endothelin receptor , muscle contraction , myofilament , contractility , biochemistry , biology , receptor , surgery , physics , quantum mechanics
1 The molecular mechanism of inotropic action of endothelin was investigated in rat ventricular muscle by studying its effects on characteristics of isometric twitch, barium‐induced steady contracture and the level of incorporation of 32 P i into myosin light chain 2. 2 Exposure of rat papillary muscle to endothelin caused an increase in isometric twitch force but did not alter the twitch‐time parameters. 3 Endothelin did not significantly change the maximum contracture tension but did cause an increase in contracture tension at submaximal levels of activation, without changes in the tension‐to‐stiffness ratio and kinetics of attached cross‐bridges. Kinetics of attached cross‐bridges were deduced during steady contracture from complex‐stiffness values, and in particular from the frequency at which muscle stiffness assumes a minimum value, f min . Endothelin did not alter f min . 4 Endothelin caused an increase in the level of incorporation of 32 P i into myosin light chain 2 without a concurrent change in the level of incorporation of 32 P i into troponin I. 5 We conclude that the inotropic action of endothelin is not due to an increase in the kinetics of attached cross‐bridges, nor due to a change in the force per unit cross‐bridge, but may result from an increased divalent cation sensitivity caused by elevated myosin light chain 2 phosphorylation, resembling post‐tetanic potentiation in fast skeletal muscle fibres.