[Calcium regulation of muscle contraction: the molecular regulation mechanisms of contracility].

The role of calcium in muscle activation is described with particular emphasis on interactions occurring between the regulatory proteins troponin-C, troponin-I, actin and myosin. These interactions depend on calcium, but in turn they also influence the calcium binding to troponin-C. They may be affected by short "competitive" peptides whose sequences are similar to the amino-acid sequences on the protein-interaction sites. They may be also affected by certain drugs (cardiotonic calcium sensitizers) that influence the calcium sensitivity of myofilaments.