Tag Archives: potassium ions

The effect of potassium different concentrations on mRNA expression of protein StAR and cytochrome P-450(scc) in human adrenocortical tissue

O. I. Kovzun, N. N. Kostuchenko, V. M. Pushkariov, O. S. Lukashenia, А. S. Mikosha

SI  V. P. Komisarenko Institute of Endocrinology and Metabolism, Academy of Medical Sciences of Ukraine, Kyiv;
e-mail: kovzun@newmail.ru

The effect of different potassium concentrations on changes in steroidogenic acute regulatory protein (StAR) and cytochrome P-450scc in human adrenal cortex tissue was studied. A rise in K+ concentration in incubation medium to 8.5 mM caused an increase in StAR and cytochrome P 450scc mRNA level in adrenocorticocytes by 70 and 76%, respectively, compared with control.  Thus, potassium ions caused an enhancement of minerocorticoid synthesis in the adrenal cortex, which is associated with mechanisms that regulate the intensity of expression of StAR and cytochrome P-450scc on a transcriptional level.

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.