The amount of Ca2+ released from the sarcoplasmic reticulum (SR) is a principal determinant of cardiac contractility. Normally, the SR Ca2+ stores are mobilized through the mechanism of Ca2+-induced Ca2+ release (CICR). In this process, Ca2+ enters the cell through plasmalemmal voltage-dependent Ca2+ channels to activate the Ca2+ release channels in the SR membrane. Consequently, the control of Ca2+ release by cytosolic Ca2+ has traditionally been the main focus of cardiac excitation-contraction (EC) coupling research. Evidence obtained recently suggests that SR Ca release is controlled not only by cytosolic Ca2+, but also by Ca2+ in the lumen of the SR. The presence of a luminal Ca2+ sensor regulating release of SR luminal Ca2+ potentially has profound implications for our understanding of EC coupling and intracellular Ca2+ cycling. Here we review evidence, obtained using in situ and in vitro approaches, in support of such a luminal Ca2+ sensor in cardiac muscle. We also discuss the role of control of Ca2+ release channels by luminal Ca2+ in termination and stabilization of CICR, as well as in shaping the response of cardiac myocytes to various inotropic influences and diseased states such as Ca2+ overload and heart failure.

The materials used for preliminary graphitizing treatment of cast iron melt (pre-modification), of which silicon carbide has the greatest technical and economic advantage, are considered. The features of the graphitizing effect of silicon carbide during the preparation of a gray cast iron melt on its structure and properties in standard cylindrical samples and clutch plate castings are analyzed. It is shown that its graphitizing effect on the cast iron melt begins to partially manifest itself already at the stage of introduction into the furnace and enhances the action of the main graphitizing modifier during subsequent ladle treatment as a result of a decrease in the content of interdendritic graphite in the microstructure.

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The article presents the investigation of the thickness of lubricating film between contacting surfaces in heavy loaded friction units, taking into account oil absorption of rough layers. Oil absorption index depends on the kind of mechanical treatment of the surfaces and makes it possible to determine necessary characteristics of the used lubricant at the design stage of a friction unit.