[The comparative efficacy and differences in the molecular mechanism of the inotropic action of cardiac glycosides and nonglycoside cardiotropic agents on the contractile protein system of the myocardium]. / Sravnitel'naia éffektivnost' i razlichiia v molekuliarnom mekhanizme inotropnogo deistviia nekotorykh serdechnykh glikozidov i neglikozidnykh kardiotropnykh sredstv na sistemu kontraktil'nykh belkov miokarda.

The in vitro study on an isolated system of myocardial contractile proteins determined optimal concentrations of the positive inotropic action and biological activity ranges of beta-methyldigoxin (beta-MD), strophanthin K, K-strophantozide, beta-acetyldigoxin (beta-AD), milrinone, and amrinone. Optimal concentrations of the beta-MD and strophanthin K (10(-2) and 10(-6) M, respectively) significantly increased qualitatively and quantitatively the economy and thermodynamic efficiency, altered the energy transformation in the contractile protein system under the isometric contraction, whereas the beta-AD produced only the quantitative effect. However, the beta-MD and strophanthin K at concentrations exceeding the optimal one by one order lost the ability to produce the qualitative effect, retaining only the quantitative one in the actomyosin ensemble. The strophanthin K significantly increased the economy of a single actomyosin ensemble in the force generation phase and the beta-MD in the tension maintenance phase. Unlike the strophanthin K, the beta-MD did not slow down (did not worsen) the relaxation process. This provides grounds to conclude that the beta-MD produces most favorable effect on the energy transformation by myocardial contractile proteins.