Tag Archives: myocytes

Seeing is believing! Live confocal imaging of microvascular networks in situ: morphology, Ca(2+) signalling and tone

T. Burdyga, L. Borysova

Department of Cellular and Molecular Physiology,
Institute of Translational Medicine,
University of Liverpool, Crown Street, Liverpool, L69 3BX, UK

2- and 3-dimensional confocal imaging of Fluo-4 loaded ureteric microvesells in situ allowed us to demonstrate distinct morphology, Ca2+ signalling and contractility in myocytes of arcade arterioles and pericytes of arcade venules. In myocytes and pericytes, Ca2+ signals arise exclusively from Ca2+ release from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate receptors. Са2+ transients in pericytes are less oscillatory, slower and longer-lasting than those in myocytes. The data obtained suggest differences in the mechanisms controlling local blood flow in precapillary arterioles and postcapillary venules.

ATP-sensitive K(+)-channels in muscle cells: features and physiological role

O. B. Vadzyuk

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: vadzyuk@biochem.kiev.ua

ATP-sensitive K+-channels of plasma membranes belong to the inward rectifier potassium channels type. They are involved in coupling of electrical activity of muscle cell with its metabolic­ state. These channels are heterooctameric and consist of two types of subunits: four poreforming (Kir 6.х) and four regulatory (SUR, sulfonylurea receptor). The Kir subunits contain highly selective K+ filter and provide for high-velocity K+ currents. The SUR subunits contain binding sites for activators and blockers and have metabolic sensor, which enables channel activation under conditions of metabolic stress. ATP blocks K+ currents through the ATP-sensitive K+-channels in the most types of muscle cells. However, functional activity of these channels does not depend on absolute concentration of ATP but on the АТР/ADP ratio and presence of Mg2+. Physiologically active substances, such as phosphatidylinositol bisphosphate and fatty acid esters can regulate the activity of these structures in muscle cells. Activation of these channels under ischemic conditions underlies their cytoprotective action, which results in prevention of Ca2+ overload in cytosol. In contrast to ATP-sensitive K+-channels of plasma membranes, the data regarding the structure and function of ATP-sensitive K+-channels of mitochondrial membrane are contradictory. Pore-forming subunits of this channel have not been firmly identified yet. ATP-sensitive K+ transport through the mitochondrial­ membrane is easily tested by different methods, which are briefly reviewed in this paper.  Interaction of mitoKATP with physiological and pharmacological ligands is discussed as well.