The role of Ca ions in restoration of the structure of interphase and mitotic chromosomes in PK living cells after hypotonic stress.

The dynamics of mitotic chromosome and interphase chromatin recondensation in living PK cells during their adaptation to hypotonic medium was studied. The recondensation process was found to be slowed down by the modification of plasma membrane with low concentrations of glutaraldehyde, while osmotic reactions of glutaraldehyde-treated cells remain unchanged. The effect of glutaraldehyde can be rapidly reversed by the addition of Ca(2+)-ionophore A23187. Intracellular Ca(2+)measurements show that the adaptation to hypotonic shock is accompanied by restoration of free Ca concentration, whereas the delay of chromatin condensation in glutaraldehyde-treated cells is paralleled by the decrease of Ca level. The mechanisms implying the role of low concentration of Ca(2+)in chromatin compactization in vivo are discussed.

Glucose strongly stimulates rate of the rRNA synthesis in Ehrlich ascites carcinoma cells.

A change in glucose concentration in an Ehrlich ascites carcinoma cell suspension from 0.1 mM to 20 mM causes a more than 50-fold stimulation of the rate of ribosomal RNA synthesis. Such an effect occurs without any dramatic effect on the rate of protein synthesis in cells. This process parallels a decrease in intracellular pH which may be a reason of Na+/H(+)-antiport activation.

[Dependence of the nature of the action of metabolic inhibitors on ribosomal RNA synthesis in Ehrlich ascites carcinoma cells on cell integrity]. / Zavisimost' kharaktera deistviia metabolicheskikh ingibitorov na sintez ribosomnoi RNK v kletkakh astsitnoi kartsinomy Erlikha ot tselostnosti kletok.

Ribosomal RNA (rRNA) synthesis in the intact Ehrlich ascite carcinoma cells is selectively inhibited by papaverin (ED50 = 0.01 mM), 2,4-dinitrophenol (DPN; ED50 = 5 microM), and actinomycin D (ED50 = 0.1 microgram/ml). The inhibition of rRNA synthesis is not connected with a direct action of these agents on the rRNA synthesis apparatus, and they had no effect on isolated cell nuclei. The rRNA synthesis in cells permeabilized with triton X-100 (0.05%) becomes insensible to the action of papaverine and DPN, but is inhibited by actinomycin D in low doses. In cells permeabilized with digitonin (0.01%) the rRNA synthesis shows no sensibility to the action of low doses of actinomycin D. The results suggest that the action of these agents on the rRNA synthesis may depend on cell integrity and on the permeabilization method employed.

[Inhibitor interaction in the suppression of ribosomal RNA synthesis in Ehrlich ascites carcinoma cells]. / Vzaimodeistvie ingibitorov pri podavlenii sinteza ribosomnoi RNK v kletkakh astsitnoi kartsinomy Erlikha.

Kinetic analysis of inhibitory action of papaverine, 2,4-dinitrophenol (DNP) and actinomycin D on RNA synthesis in the intact Ehrlich ascites carcinoma cells has shown that the action of these agents is mediated by their effect on the same step of rRNA synthesis.

[Effect of 2,4-dinitrophenol on the synthesis of ribosomal RNA in the cells of Ehrlich ascitic carcinoma under anaerobic conditions]. / Vliianie 2,4-dinitrofenola na sintez ribosomnoi RNK v kletkakh astsitnoi kartsinomy Erlikha v anaérobnykh usloviiakh.

It is shown that 2,4-DNP (20 mkM to 1 mM) selectively inhibited RNA synthesis in Ehrlich ascite carcinoma cells both in aerobic and in anaerobic conditions in equal extent. It is supposed that the inhibitory action of DNP is not associated with its influence on oxidative phosphorylation and intracellular ATP concentration, but may be accounted for cell reaction to non-specific actions.

[Effect of cycloheximide, 2,4-dinitrophenol and papaverine on ribosomal RNA synthesis in Ehrlich ascitic carcinoma cells]. / Vliianie tsiklogeksimida, 2,4-dinitrofenola i papaverina na sintez ribosomal'noi RNK v kletkakh astsitnoi kartsinomy Erlikha.

The influence of 2,4-dinitrophenol (DNP), papaverine and cycloheximide on RNA synthesis in Ehrlich ascites tumour cells has been investigated. All above mentioned agents inhibit selectively synthesis of high-molecular rRNA precursor, when the cell population density is 3.10(7)--5.10(7) per 1 ml of suspension. When the density of cells decreases as far as 1.10(6) cells per 1 ml. the rRNA synthesis loses the sensitivity to all these agents. The effects of both cycloheximide on the protein synthesis and DNP on ATP level do not depend on the cell population density in suspension. It is suggested that either with a decrease of cell population density the protein synthesis and ATP level cease playing the role of a rate-limiting factor in the rRNA synthesis, or the influence of agents studied is realized by means of their interaction with other cell system.

[Effect of a number of metabolic inhibitors and other biologically active substances on the development of sea urchin embryos]. / Vliianie riada metabolicheskikh ingibitorov i drugikh biologicheski aktivnykh veshchestv na razvitie zarodyshei morskogo ezha.

Benzo(a)pyrene, hydrocortisone, corticosterone, ethidium bromide, actinomycin D and papaverin arrested the development of sea urchin embryos at the stage of early gastrula when the synthesis of rRNA increases. The fertilization membrane did not prevent the penetration of hydrocortisone and benzo(a)pyrene in the embryo cells. These drugs did not affect RNA synthesis at the early stages of development and markedly suppressed it at the early gastrula stage. A suggestion is put forward to the effect that the developmental arrest at the early gastrula stage is connected with the suppression of rRNA synthesis. The mechanism of selective sensitivity of rRNA synthesis to a wide range of biologically active substances is discussed.