Effect of Ca2+ gradient on the structure of sarcoplasmic reticulum membranes.

The structure of sarcoplasmic reticulum membranes was studied in the presence of modeled transmembrane Ca2+ gradient corresponding to the status of Ca2+ depot at different stages of the muscle contraction-relaxation cycle in health and disease. Various sites of the membrane were characterized using spectral analysis of tryptophan, pyrene, and merocyanine-540 fluorescence without evaluating specific changes in the molecules of membrane components (Ca2+ -ATPase, ryanodine receptor, and lipids). The transmembrane Ca2+ gradient modulates the protein-lipid interactions and structural characteristics of the membrane. The proposed model can be used for studies of the effects of pharmacologically active substances and endogenous regulators.

Changes in the structure and functions of membranes in erythrocytes and Ehrlich ascites carcinoma cells under the influence of a new generation hybrid antioxidant IKhFAN-10.

We studied the effect of a new generation hybrid antioxidant IKhFAN-10 on the structure and function of cell membranes (organization of the lipid bilayer and proteins and activity of ion channels). The test preparation proposed for the therapy of neurodegenerative diseases modified properties of membranes in erythrocytes and Ehrlich ascites carcinoma cells and affected functional activity of cells. We determined the doses of this antioxidant, which did not cause side effects.

Fusion and endocytosis of anionic liposomes with Ehrlich ascitic carcinoma cells.

Polyethylene glycol 300 and low pH of the incubation medium initiate fusion of anionic lipid liposome membranes with Ehrlich ascitic carcinoma cell membranes. Some liposomes are endocytosed in cells and are distributed near the inner surface of the membrane. Liposome membranes spontaneously fuse with the cells under certain conditions.

[Comparison of the catalytic and structural properties of Ca2+-ATPase in longitudinal tubules and terminal cisternae of the sarcoplasmic reticulum]. / Sravnenie kataliticheskikh i strukturnykh svoistv Ca2+-ATPase v prodolgovatykh trubochkakh i terminalnykh tsisternakh sarkoplazmaticheskogo retikuluma.

The catalytic behavior and structural features of Ca2+-ATPase in the vesicles of longitudinal tubules and terminal cisternae of the sarcoplasmic reticulum isolated from rabbit skeletal muscles was analysed. pH measurements have shown under optimal conditions Ca2+-ATPase has similar catalytic behavior both in the fractions of longitudinal tubules and terminal cisternae. Under non-optimal conditions, the behavior similarity was not observed. The specific activity of the ATPase enzyme under optimal conditions was shown to be much higher in the fraction of longitudinal tubules than in the fraction of terminal cisternae. Caffeine added to both fractions had no effect on the catalytic behavior of Ca2+-ATPase. As judged from fluorescence analysis, the structure of Ca2+-ATPase of longitudinal tubules differs from that structure of terminal cisternae. In sarcoplasmic reticulum membrane, at least half of the tryptophan residues of Ca2+-ATPase was shown to be buried in the lipid bilayer. Our findings suggest that in terminal cisternae some of the Ca2+-ATPase molecules exist as an oligomeric protein and do not participate in ATP hydrolysis (named "silent" Ca2+-ATPase).

[Activation of the caffeine center of the sarcoplasmic reticulum at a reduced concentration of magnesium ions]. / Aktivatsiia kofeinovogo tsentra sarkoplazmaticheskogo retikuluma pri snizhenii kontsetratsii ionov magniia.

The action of caffeine and Mg2+ on the efficacy of Ca2+ transport by terminal cisterns and longitudinal tubules of rabbit skeletal muscle sarcoplasmic reticulum (SR) was studied and compared. Addition of 5 to 10 mM caffeine to the incubation medium or a decrease in Mg2+ concentration from 4 to 0.1 mM led to a 3-fold diminution of the Ca/ATP ratio for the terminal cistern fraction. In longitudinal tubules, that effect was far less pronounced. The effects of caffeine and decreases in Mg2+ concentration were blocked by ruthenium red, tetracaine and dimethylsulfoxide. It is assumed that the decrease in Mg2+ concentration is accompanied by activation of the caffeine site of the SR, induced by the intravesicular caffeine-like factor.

[Intracellular localization of the caffeine-sensitive form of Ca-dependent ATPase in the sarcoplasmic reticulum]. / Vnutrikletochnaia lokalizatsiia kofeinchuvstvitel'noi formy Ca-zavisimoi ATFazy sarkoplazmaticheskogo retikuluma.

A Ca-selective electrode was used to study the effect of caffeine on different fractions of sarcoplasmic reticulum membranes of rabbit skeletal muscles. Caffeine was found to uncouple Ca2+ transport and ATP hydrolysis in a fraction, which is enriched with fragments of terminal cisterns according to the electron microscopy data. Caffeine does not produce any effect on the light fraction containing no fragments of terminal cisterns. It is concluded that caffeine-sensitive Ca2+-dependent ATPase is localized in terminal cisterns of the sarcoplasmic reticulum.

[Mechanisms of the damaging effect of fluorescent dyes on the retina]. / Mekhanizmy povrezhdaiushchego deistviia fliuorestsentnykh krasitelei na setchatku glaza.

Mechanisms of the photo-damage of a fluorescent dye (methylene blue) and of the protective action of antioxidants and quenchers of singlet oxygen on the outer retinal rod segments (ORRS) and retinal function in situ and in vivo were studied. The methylene blue-induced formation of singlet oxygen in the ORRS resulted in accumulation of lipid peroxidation products, oligomerization of rhodopsin, and in a decrease in rhodopsin thermal resistance. Modification of the lipid and protein components of the visual cells by singlet oxygen inhibited the electrical activity of both isolated frog retina in situ and rabbit retina in vivo (waves a and b on the electroretinogram). The antioxidants (alpha-naphthol, alpha-tocopherol, 4-methyl-2,6-di-tert-butylphenol) and singlet oxygen quenchers, [1,4-diazabicyclo (2,2,2)octane] and alpha-tocopherol prevented the damaging effects of the fluorescent dye induced by singlet oxygen formation.