[Calcium regulation by troponin and its genetic disorder in striated muscle contraction]

Contraction of skeletal and cardiac muscles is regulated by Ca2+ through specific Ca(2+)-regulatory proteins, troponin and tropomyosin, located in the thin filament. Troponin is a Ca2+ receptive protein consisting of three differet components, troponins C, I, and T. The essential mechanisms of Ca(2+)-regulation are the inhibition of contractile interaction between myosin and actin by the inhibitory action of troponin I and the reversal of the inhibition by troponin I through the Ca(2+)-binding to troponin C. All three components of troponin are required for the Ca(2+)-regulation of contraction. This article reviews following aspects of troponin researches: 1) early studies on the structure and function of troponin, 2) molecular mechanisms of Ca(2+)-regulation, 3) principles of troponin-exchange in skinned fibers and properties of troponin isoforms thereafter clarified under physiological conditions, 4) recent studies on the functional consequences of the mutations in human cardiac troponins T and I that cause genetic disorders, familial hypertrophic cardiomyopathy (HCM), and familial dilated cardiomyopathy (DCM).