Contractile proteins: possible targets for the cardiotonic action of MCI-154, a novel cardiotonic agent?

The effect on the contractile protein system of MCI-154, a novel and potent cardiotonic agent, was examined by using thin bundles of chemically skinned fibers from the guinea-pig papillary muscles. MCI-154 increased the Ca2+ sensitivity of the contractile protein system of the cardiac skinned fibers. Moreover, MCI-154 enhanced the maximum tension developed at pCa 4.4. These results suggest that an increase in responses of the contractile protein system to Ca2+ ion is, at least in part, responsible for the positive inotropic action of MCI-154.