S100A1 modulates skeletal muscle contraction by desensitizing calcium activation of isometric tension, stiffness and ATPase

S100, a subfamily of the EF-hand type calcium sensing proteins, is implicat ed in many cellular functions including muscle contractility. Two isoforms, S100A1 and S100B, at 2-10 muM significantly inhibit active tension, stiffn ess and ATPase of skinned single rabbit psoas muscle fibers at submaximal ( pCa similar to 6.1-5.6), but not at maximal levels of activation (pCa 4.0). S100A1 is a more potent inhibitor than S100B. Hill analysis of the ATPase- pCa and tension-pCa curves indicates that these proteins reduce calcium sen sitivity and enhance the cooperativity toward calcium. We propose S100A1, a nd perhaps S100B, are viable candidates as physiological modulators of musc le contraction. (C) 2001 Published by Elsevier Science B.V. on behalf of th e Federation of European Biochemical Societies.