Mathematical modeling of transmembrane calcium transport kinetics in smooth muscle cells

A mathematical model, which describes kinetics of transmembrane calcium transport in a smooth muscular cell, has been elaborated and investigated taking into account that the change of calcium cations concentration within a cell is determined by two mutually opposite processes: an increase of a carrying capacity of calcium channels of plasma membrane under signal substance action and calcium removal from the intracellular space by Mg2+, ATP-dependent calcium pump localized on the plasma membrane. The fundamental difference of the proposed model against the models analyzed in literature before is that the cellular system returns to the initial stationary state after enzyme-catalysed transformation of the signal substance. The results of calculations showed that this model really described the experimental kinetics of the transmembrane calcium transport. In this paper the influence of different parameters (Michaelis constant and ultimate rate of calcium pump, initial concentrations of signal substance and enzyme decomposing it, rate constants) on kinetics of calcium transport through the plasma membrane has been investigated in detail.     

Influence of direct electric current on hydrodynamic diameter of human serum albumin

The effect of the weak electric current (2 mA/cm2) on structural characteristics (hydrodynamic diameter and molecular weight) of the human serum albumin (HSA) was studied using photon correlation spectroscopy (PCS). The average diameter of initial HSA globule is approximately 7 nm (66.8 kDa). After electric current treatment during 2-5 min the diameter of HSA monomer increases to 7.5 nm. The duration of electric current treatment being increased to 20 min the size of HSA monomers decreases to 6.4 nm. The behaviour of HSA oligomers is close to that of monomers. Consequently, changes in the sizes of monomers and oligomers of HSA under the electric current treatment are caused by the change in the charge density stimulating change of tertiary structure of molecules and possible addition of ions from the buffer solution to them.     

Na+,K(+)-ATPase activity in human colorectal carcinoma

Na+,K(+)-ATPase activities in macroscopically unchanged mucosa (conditionally normal tissue) and human colorectal carcinoma (mainly low-grade and moderately differentiated adenocarcinomas) have been investigated. Microsomal fractions are similar by dimensions of the membrane fragments detected by photon correlation spectroscopy analysis. The activation optima under digitonin pretreatment of the membrane fractions differ significantly for Na+,K(+)-ATPase and concomitant Mg(2+)-ATPase activity, but are the same in conditionally normal and cancerous tissues. This allows to detect correctly total levels of the Na+,K(+)-ATPase activity in the detergent-pretreated preparations. The moderate decrease of the Na+,K(+)-ATPase activity is revealed in carcinomas. It is concluded that a decrease of activity of the ouabain-sensitive human Na+,K(+)-ATPase is characteristic of colorectal carcinoma.     

Docking and fusion of synaptic vesicles in cell-free model system of exocytosis

The present study involves the testing and characterization of synaptic vesicle (SV) docking and fusion as the steps of exocytosis using two different approaches in vitro.The interaction of SVs was determined by the changing of particles size in suspensions by the method of dynamic light scattering (DLS). Fluorescence assay is represented for studying the mechanism of SV membrane fusion. The sizes of membrane particles were shown to increase in the medium containing cytoplasmic proteins of synaptosomes. Therefore, the cytosolic proteins are suggested to promote the SVs into close proximity where they may become stably bound or docked. The specific effect of synaptosomal cytosolic proteins on the interaction of SVs in the cell-free system was demonstrated. The incubation of SVs with liver cytosol proteins or in the bovine serum albumin solution did not lead to the enlargement of the particles size. The fusion reaction of the SVs membranes occurred within the micromolar range of Ca²⁺ concentrations. Our studies have shown that in vitro process of exocytosis can be divided into Ca²⁺-independent step, termed docking and followed by fusion step that is triggered by Ca²⁺. The role of cytosolic proteins of synaptosomes in docking and fusion of SVs in cell-free system was further confirmed.     

Antimicrobial activity of stable silver nanoparticles of a certain size

Conditions for obtaining stable silver nanoparticles smaller than 10 nm were developed using a binary stabilizer polyvinylpyrrolidone/sodium dodecylsulphate in optimal ratio. Optical spectra, morphology and dependence of size of the nanoparticles on the amount of reducing agent were studied. Colloidal solutions of nanosilver showed a high bactericidal activity against strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, and fungicidal activity against Candida albicans. The mechanism of action of nanosized silver on microbial cell was examined by laser scanning confocal microscope using fluorescent label. First step of antimicrobial effect on microorganisms was membrane damage and penetration of silver nanoparticles into the cell. Prolonged stability of nanoparticles and their antimicrobial activity over the past two years were showed.     

Kinetic modeling of enzyme-catalysed reactions with participation of activators applied to ATP hydrolysis by Mg2+- ATPase

Theoretical investigation of the model of reaction of ATP hydrolysis by "basal" Mg2+-ATPase has been carried out. It has been assumed that during the reaction each of three reacting substances (Mg2+, ATP, enzyme) can combine into complexes in couples with other participants of this process. Then the third component can associate with formed complexes producing the ternary complex of enzyme-activator-substrate. Such approach allowed to take into account all possible interactions in the chosen system, to investigate overall process in detail avoiding any simplifications and to find such peculiar properties of the process which will allow to understand the reaction mechanism and to explain observed experimental data. All possible pathways of the ATP hydrolysis process have been examined separately and as a whole. It is shown that if the reaction proceeds via two or three possible pathways then maximums are observed on plots of initial reaction rate on concentration ATP or magnesium. In addition maximums are also observed when enzyme concentration is increased. It is qualitatively new result that does not follow from the existing theories. The obtained results permit to explain some experimental data of ATP hydrolysis, active ion transport and some other reactions in a new fashion. The studied model and obtained results may be applied to another enzyme-catalysed reactions which proceed in the activator presence.     

Comparative investigation by spectrofluorimetry and flow cytometry of plasma and inner mitochondrial membranes polarisation in smooth muscle cell using potential-sensitive probe DiOC6(3)

Possibility of the use of flow cytometry and spectrofluorimetry analysis for investigation mitochondria and plasma membrane polarization in myometrium cell suspension using potential-sensitive probe 3,3'-dihexyloxacarbocyanine [DiOC6(3)] has been demonstrated. The obtained results confirm the use of DiOC6(3) for studying the influence of effectors on transmembrane potentials of intact cell compartments.