Nucleoside diphosphate kinase and GTP-binding proteins. Possible mechanisms of coupling

The results of numerous investigations during the last 20 years show that nucleoside diphosphate kinase (NDP kinase) is a multifunctional protein. In this paper, the current data are analyzed indicating that one of the possible mechanisms by which NDP kinase manifests its multifunctional role is its participation in the activation (or regulation) of heterotrimeric GTP-binding proteins (G proteins). We demonstrate that one of the NDP kinase isoforms dynamically interacts with the retinal rod G protein transducin (Gt) and phosphorylates its β-subunit at histidine residue (His 266). It is also shown that it leads to the consecutive transfer of the phosphate group to GDP in the active center of G protein α-subunit and G protein activation. The advantages of this mechanism are considered as compared to the classic G protein activation mechanism, GDP/GTP exchange.     

The mechanisms of ion transport activation with a change in cell volume]

The review deals with literature and our own experimental data on the possible mechanisms of activation of the ion transport in cells during the change of their volume. The involvement in this process of calcium, cyclic mononucleotides, metabolites of polyphosphoinositides and arachidonic acid, as well as the membrane carcass and cytoskeleton are discussed.     

Effect of melittin on ion currents in heart cell membranes

It has been shown on auricle fibres of the frog that neurotoxin from bee poison melittin suppresses the ionic currents entering the cell through calcium and sodium channels of the membrane, increases the background potassium current, suppresses phasic and tonic contraction of the fibres. Toxin modifies the kinetics of calcium channels, but does not affect activation and desensitization of beta adrenoreceptors. Effects of melittin are not decreased when adding the inhibitor of phospholipase A2 indomethacin. The results show that melittin directly affects the protein components of the membrane-ionic channels, probably binding with them.     

Rheological properties of the blood and erythrocyte suspension after exposure to zootoxins

The rheological properties of blood (viscosity, suspension stability and deformation of red blood cells) have been studied under the influence of zootoxins. It has been shown that the toxins Apis mellifera, Mesobuthus eupeus, Agkistrodon blomhoffii in vitro exert essential effect on haemorheological indexes.     

Estradiol receptors in the rat uterus under long-term hormone administration at different doses

Multiple administration of estrogens in doses of 1 and 10 micrograms reduces specific binding of 3H-estradiol by subcellular fractions of rat uterus tissues. The cytoreceptor apparatus of the uterus of androgen-sterile rats is marked by the decreased response to a prolonged (7-8 days) hormone administration as compared to responses seen in normal and ovariectomized animals. The depletion of estrogen receptors is not linked with a rise of the endogenous steroid level in blood plasma and cytosol from uterine tissues.     

Effect of the neurotoxin apamin on ion currents in membranes of heart fibers

It has been shown on auricle fibres of the frog that neurotoxin apamin in extremely low concentrations (10(-10)-10(-9) M) suppresses the current entering in the cell through calcium channels of the membrane, but it increases tonic contraction related to Na/Ca exchange. No significant effects on fast sodium and potassium channels were observed. The results show that the mechanism of apamin effect on the heart is to a large extent conditioned by specific influence on Ca transport through the cell membranes.     

Osmotic regulation of the sodium pump in rat brain synaptosomes]

Effect of medium osmolarity on 3H-ouabain binding and the rate of ouabain-sensitive 86Rb+ transport in the rat brain synaptosomes was studied. A decrease in tonicity to 230 mOsm increases both parameters indicating the activation of the sodium pump upon synaptosome swelling. The effect is retained in the absence of inside-oriented Na+ gradient, i. e. a rise in Na(in) is not responsible for hypoosmotic activation. Colchicine (5mM) decreased and cytochalasin B (40 microM) increased the ouabain binding. In the presence of cytochalasin B the inhibition of binding observed under hypotonic conditions was shifted to higher osmolarity values. It is suggested that volume regulation of the sodium pump is controlled by the cytoskeleton elements.