[The role of changes in the cytoplasmic concentration of Ca2+ in dexamethasone-induced thymocyte death].

The putative role of changes in cytosolic Ca2+ concentration ([Ca2+]i) in the dexamethasone (DM) induced thymocyte death was investigated. Incubation of rat thymocytes with 10(-7) M DM for different time intervals from 0.1 to 8 h did not change the basal [Ca2+]i level ca 100 nM as measured with Ca(2+)-fluorescent probe Quin-2.

[Effect of bacterial toxins on the mitogen-induced increase of the Ca2+ concentration in the cytoplasm of rat thymocytes. The role of N proteins].

The effect of bacterial toxins, modifying the activity of regulatory N proteins of adenylate cyclase and probably other systems, on the mitogen-induced changes of cytosolic free Ca2+ concentration ([Ca2+]i) has been studied using Ca2+ fluorescent probe quin-2. It is shown that treatment of thymocytes with cholera toxin, E. coli heat-labile (HL) toxin or pertussis toxin abolishes the concanavalin A (con A)-induced rise of [Ca2+]i.

[Changes in pH in the cytoplasm of rat thymocytes after treatment with the mitogen concanavalin A and protein kinase C activator phorbol ester].

The intracellular pH (pHi) of rat thymocytes has been measured with the fluorescent probe 2', 7'-bis(carboxyethyl)-5,6-carboxyfluorescein, both in the resting cells and under mitogenic stimulation. Concanavalin A (Con A) has been found to increase pHi from 7.16 +/- 0.

[Effect of SH-reagents on Ca2+ level in lymphocyte cytoplasm].

The effect of SH-reagents on cytoplasmic free Ca2+ concentration [( Ca2+]i) in rat thymocytes and B lymphoma Raji cells has been studied by means of fluorescent Ca2+ indicator quin-2. N-ethylmaleimide and ethylmercurythiosalicylate have been found to induce a dose-dependent increase of Ca2+ concentration from about 100 nM in the control cells up to 1000 nM. The effect is weakened with a decrease of the external Ca2+ concentration and is not observed already with Ca2+ concentration in the medium less than 0.

[Effect of quinine, a blocker of Ca2+-activated K+-channels, on lymphocyte activation by mitogens].

Quinine inhibits mitogenesis at the same concentration (10(-4) M) as that which blocks Ca++-dependent potassium transport in lymphocytes. Lower quinine concentrations (10(-8)-10(-6) M) induce a comitogenic effect which is most pronounced when Ca++-ionophore A23187 is used as a mitogen. Thus, activation of Ca++-dependent K+-channels is not necessary to trigger mitogenesis, but is important for further stages of the process.

[Effect of Ca2+-ionophore and concanavalin A on potassium permeability and membrane potential of thymocytes].

The existence of Ca2+-dependent K+ channels in rat thymocytes, their activation by Ca2+-ionophore A23187 and concanavalin A, and inhibition by EGTA and quinine have been demonstrated using K+-electrode and fluorescent potential probe diS-C3-(5). The results indicate that Ca2+-dependent K+ channels take part in the increase of potassium permeability, one of the early events in mitogenic stimulation of lymphocytes.

[Effect of calmodulin blockers on membrane potential, potassium permeability and lymphocyte mitogenesis].

The effects of calmodulin antagonists--trifluoperazine and chlorpromazine--on the membrane potential, K+ efflux and mitogenic response of rat thymocytes and human peripheral blood lymphocytes were investigated. Phenothiazines were found to produce depolarization in both types of lymphocytes even when taken at micromolar concentrations. This effect was not caused by the inhibition of the Na+,K+-pump or by a decrease in K+ permeability of the lymphocyte membrane.

[Effect of adenosine protonation on its interaction with polyuridylic acid].

The effect of adenosine protonation on complex formation between poly(U) and adenosine has been studied by UV spectroscopy, titration and equilibrium dialysis techniques. A method has been developed to estimate the "misincorporation" of ionized monomer molecules into a polynucleotide--monomer complex. The method is based on combining the titration and binding data.

[Effect of ionization of system components on the interaction of polyuridylic acid with adenosine. Deprotonation of the polynucleotide].

The interdependence of complex formation and poly(U) deprotonation in the poly(U)-adenosine system has been studied by UV spectroscopy, titration and equilibrium dialysis techniques. Evidence is presented on the formation of an intermediate, probably double helical, structure in the course of A-2 poly(U) dissociation at alkaline pH.

[Polycytidylic matrix complex formation with complementary and noncomplementary purine nucleoside triphosphates].

Misincorportion into I poly(C) : I GTP complex, alpha = (formula: see text), has been determined by using H3-ATP. At ATP total concentration increasing from 6X10(-6) M to 4.5X10(-3) M the alpha value increases going asymptotically onto a plateau.

[Reaction between polycytidylic acid and guanosine-5'-triphosphate at neural pH].

The effect of changing the solution acidity in the interval of pH 7--8 on complex formation between polycytidilyc acid (polyC) and guanosine-5'-triphosphate (GTP) has been studied by the equilibrium dialysis and hydrogen ion titration methods. It is shown that in 1 M NaCl at 3 degrees C the complex stoichiometry undergoes changes in a narrow pH interval being equal to 2 poly C: 1 GTP at pH 7,0--7,3 and to 1 poly C:1 GTP at pH 7,6--8,0. In the presence of GTP the apparent pK of poly C protonation increases by 1,4 PK units and becomes equal to 7,1 in 1 M NaCl at 3 degrees C.