[Interactions of vanadate with the contractile system of the rabbit psoas muscle in active, relaxed and rigor states].

Interaction between 0.1-0.3 mM vanadate (Vi) and muscle fibres was studied by measuring their force and stiffness. Only interaction with the fibres having cycling cross-bridges caused a strong decrease of these parameters. There was no vanadate effect on the rigor fibres and its complexes with Mg.AdP or Mg.beta-gamma-imido-ATP. Judging by the following transient tension in Vi-containing solutions Vi was slowly incorporated into relaxed fibres, Vi complex with muscle was stable under relaxation conditions, but it was splitted when actomyosin was formed. Formation of M.ADP.Vi+, the stable biochemical analogue of M.ADP.Pi ( Goodno C. C., Taylor E. W. Proc. Natl. Ac. Sci. USA, 1982, 79, p. 21) is assumed to be formed in muscle. On the basis of the difference between rigor contraction of ATP- and Vi-relaxed fibres a conclusion can be drawn that the Vi complex in muscle is not a mechanochemical analogue of the myosin intermediate developing force when interacting with actin.