On the mechanism of shrinkage-induced potassium influx in rat and human erythrocytes.

The rates of 86Rb influx into human and rat erythrocytes were studied in media of various tonicity. At sucrose concentrations below 0.3 mol/l, the ouabain-insensitive, furosemide-inhibited component of influx increased in rat but not in human erythrocytes; this may be explained by a rise in the rate of Na+, K+, Cl-- and/or K+, Cl-cotransport. An increase in osmolarity resulted in a reduction of this as well as of the ouabain and furosemide-insensitive component in rat erythrocytes. At the same conditions a drastic inhibition of Na+, K(+)-pump occurred both in rat and human erythrocytes. We failed to observe a lag-phase in the activation of the cotransport in rat erythrocytes; i. e. the process of activation parallels the shrinkage of cells. In rat erythrocyte ghosts, the shrinkage-induced stimulation of the cotransport was lost, and the direction of their osmotic reaction (inhibition of transport pathways) was similar to that in human erythrocyte ghosts. It is suggested that the mechanism of volume regulation of ion transport in intact cells involves a step of physical amplification via a change in interactions between the protein carcass and the lipid bilayer.     

Kinetic characteristics of 22Na transport in human and rat erythrocytes during cytoplasm acidification and cell compression

Under normal conditions (pH0 = 7.4, pHi = 7.1-7.2) amiloride, a Na+/H+ exchange inhibitor, does not influence Na+ intake by human and rat erythrocytes. Acidification of the cytoplasm (pHi approximately 6.4) is accompanied by the acceleration of 22Na intake, which is decreased after addition of 1 mM amiloride (by 50 and 80%, respectively). The Ki value of amiloride for human and rat erythrocytes is 30 and 250 microM, respectively. In rat erythrocytes the dependence of the rate of the delta pH-induced incorporation of 22Na on Na+ concentration is described by a saturation curve (K0.5 for Na0+ is approximately 40 mM), whereas in human erythrocytes it obeys the diffusion kinetics. These results suggest that the Na+/H+ exchange takes place in rat erythrocytes, but is absent in human erythrocytes. In rat erythrocytes the Na+/H+ exchange can be induced by cell compression which can be caused either by decreasing the KCl content (after addition of valinomycin) or by increasing the osmolarity of the medium (in the presence of sucrose). The rate of Na+/H+ exchange induced by cell compression is increased by 60-70% after addition of protein kinases A and C activators. No effect of intracellular Ca2+ on the rate of the Na+/H+ exchange in rat erythrocytes is observed.     

Mathematical model of cooperative work of ion pump,symport and antiport in epithelial cells

Transcellular transport in epithelial cells plays an important role in providing such physiological functions as excretion of cytotoxic substances or reabsorption of metabolites useful for the body life activity. These functions have been shown to be performed by the mechanisms—symport, antiport, ion pumps, and channels—that often function cooperatively. Models for kinetic peculiarities of the substrate transport with the aid of the above mechanisms are widely described in the literature. Much less attention is paid to modeling of cooperative activity of transporters that have different transport mechanisms. In this work we propose a mathematical model for flux coupling of three transporters—the ion pump, symporter, and antiporter as well as of two substrates, one of which (A) can be transported simultaneously by the symport and antiport mechanisms, while the other (B)—only by the latter mechanism. Analysis of the model has shown that for the pair of substrates (A and B) the flux coupling becomes possible if the following conditions are met: (1) the substrate A flux into the internal cell volume using the symport mechanism is to exceed its antiporter-realized flux in the opposite direction; (2) probability of reorientation from one side of membrane to the other side for the antiporter loaded with the substrate is to be essentially higher than that for empty transporter. The proposed model can be used for comparing efficiency both of excretion and of reabsorption of cell metabolites in representatives of different taxa.     

Cytophotometric study of the AChE-containing nerve cells and fibers of the rabbit heart after electrostimulation of the area hypothalamica posterior

By means of cytophotometry and a computer in the cardiac intramural neural plexus of 17 experimental and 17 control rabbits acetilcholine esterase (AChE) activity (revealed by Karnovsky--Roots' method) was investigated. It was stated that a prolonged electrostimulation of the area hypothalamica posterior (AHP) produced statistically significant 2-fold decrease of AChE activity in the cardiac neural cells and fibres. When the stimulation of AHP was stopped, the decreased enzymatic activity was observed for the first two weeks, then by the end of the 4th week it again reached its control level. The results of the work were discussed in view of possible disorders of regulating vegetative-trophic effects of the posterior hypothalamus on innervative and executive tissue elements of the heart.     

Synthesis of GnRH analogues and their application in targeted gene delivery systems

A set of GnRH analogues containing the nuclear localization signal (NLS) of the SV-40 virus was synthesized using solid phase peptide synthesis and chemical ligation techniques. Selective chemical ligation was achieved through hydrazone formation upon the interaction of NLS hydrazide and GnRH analogue modified with pyruvic acid. The efficiency of the synthesized compounds was demonstrated in experiments on transfection of various human cancer cell lines with reporter luciferase and β-galactosidase genes, as well as suicide thymidine kinase gene of HSV-1. Selectivity of the peptide-DNA complex effect on cancer cells is achieved as a result of its penetration through the cell membrane via GnRH receptor-mediated endocytosis pathway.     

Theoretical and experimental studies of the radiative properties of matter at high energy densities and their application to the problems of inertial confinement fusion

The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition, are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and (C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial confinement fusion experiments with the use of laser radiation and heavy-ion beams.