[COMPARATIVE STUDY OF Y³âº EFFECT ON CALCIUM-DEPENDENT PROCESSES IN FROG CARDIAC MUSCLE AND IN MITOCHONDRIA OF RAT CARDIOMYOCYTES].

Inotropic effects of yttrium acetate (Y³âº) on contractions of myocardium preparations of the frog Ra- na ridibunda as well as on respiration and the inner membrane potential (Δψmito) of isolated rat heart mi- tochondria were studied. It was found that 2 mM yttrium in Ringer solution significantly reduced the am- plitude of myocardium contractions evoked by electric stimulation and increased the half-relaxation time (n = 5). In experiments with Ca²âº, Y³âº decreased Ca²âº-dependent oxygen consumption rate of rat heart mitochondria, energized by glutamate and malate, impeded the reduction in respiration of these mito- chondria in state 3 or uncoupled by 2,4-dinitrophenol, and inhibited Ca²âº-induced decrease in their inner membrane potential. These data are important to better understand the mechanisms of Y³âº effects on myocardial calcium-dependent processes. Possible mechanisms of negative inotropic effect of Y³âº on the myocardium and its influence on the Ca²âº-dependent processes in rat mitochondria are discussed.

[Inotropic effect of a new probiotic product on myocardial contractility. Comparison with diazoxide].

The inotropic effect of a new probiotic product on myocardial contractility of the frog Rana ridibunda and the effect of probiotic product on the rat cardiac mitochondria swelling were studied. In both cases, the comparison with known cardioprotector diazoxide was done. Probiotic product and diazoxide were shown to cause a dual effect on the maximum force induced by the muscle sample during spontaneous atrial contraction. Addition of agents caused a negative impact, while washing out exerted a positive inotropic effect. At the same time probiotic product has virtually no effect on the amplitude of contraction induced by electrical stimulation of the ventricle fragments. Probiotic product decreases both proton passive permeability in the inner mitochondrial membrane, and potassium active transport in mitochondria caused by activation of K(+)-uniporter of cardiomyocytes. A possible mechanism of action of probiotic product is discussed.

[Slow calcium waves in cultured postnatal rat skeletal myocytes].

A variety of active agents increasing [Ca2+]i in cultivated skeletal myocytes have been investigated. It was shown that, out of the agents such as noradrenaline, carbacholine, caffeine, cyclopiazonic acid, and potassium solution, only the last caused the formation of slow calcium waves in skeletal myocytes. These waves propagated not only near the location of the cell nucleus but also along the whole length of myocytes. It is supposed that this wave process can be related to the modulation of excitation-relaxation processes in skeletal muscles.

[A decrease in the damaging action of gamma irradiation on human lymphocytes by postradiation treatment with the preparation MDI]. / Snizhenie povrezhdaiushchego deistviia gamma-oblucheniia na limfotsity cheloveka pri postluchevoi obrabotke preparatom MDI.

The effect of MDI, the agent of plant origin, on the cell cycle and the number of micronuclei in human lymphocytes after gamma-irradiation has been studied. It has been found that the treatment of lymphocytes with MDI stimulates DNA synthesis and reduces the delay of irradiated cells in (G2 + M) phase. Moreover post-irradiation cell treatment with MDI reduces the number of damaged cells.

[The contractile properties of the frog muscle fiber in the intact and the skinned states]. / Sokratitel'nye svoistva myshechnogo volokna liagushki v intaktnom i v skinirovannom sostoianiiakh.

The comparison of force-velocity (p-V) relation was made for live and chemically skinned frog skeletal muscle fibers. The latter fibers revealed steeper p-V curves. Maximal isometric tension in these fibers was 27 per cent less. The maximal velocity of unloaded shortening was 15 per cent greater.