CROSS-BRIDGE-DEPENDENT CHANGES IN THE INTRACELLULAR CA2+ CONCENTRATION IN MAMMALIAN CARDIAC MUSCLES

A change in muscle length significantly alters the developed tension i n mammalian cardiac muscle compared to that in skeletal muscle fibers. The intracellular mechanisms related to the length-dependent change i n developed tension have been studied using Ca2+ indicators in intact preparations; a cross-bridge-dependent change in the affinity of tropo nin-C for Ca2+ is a possible mechanism. This hypothesis is further sup ported by the measurement of Ca2+ bound to troponin-C in skinned prepa rations. The molecular mechanism of the cross-bridge-dependent change in the affinity of troponin-C for Ca2+ is not fully understood althoug h the studies which employ the substitution of troponin-C in skinned p reparations, transgenic animals and in an animal model with heart dise ase have been performed. We reviewed the current studies by analyzing the intracellular mechanism responsible for the length-dependent chang e in tension development in mammalian cardiac muscle.