Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Study of the effect of microconcentrations of glucose on the biosynthesis of penicillin]

A method of "acute" experiments with significant dilution of the fermentation broth is proposed for studying the effect of easily assimilable substrates on growth of the culture and production of the antibiotic by it. The effect of microconcentrations of glucose on the parameters of the process kinetics was studied with respect to penicillin. The specific effect of microconcentrations of glucose on the specific rate of the culture growth and productivity was noted.     

Intra- and interspecies differences in the ISSR-PCR patterns of bumble bee (Hymenoptera: Bombinae)

Variation in the ISSR patterns was studied in queens of five species of bumble bee habitating on the territory of Ukraine and Belarus. Species-specific characteristics were obtained for B. sylvarum, B. lapidarius, B. pascuorum, B. terrestris, and B. hortorum with using (GTG)7A and (AGC)6G as primers. Some ISSR markers were common for the groups of species. From 73 to 100% ISSR markers were invariant within the species. Individual characteristics of B. terrestris from geographically distant populations from Kiev and Minsk Oblasts were similar. The level of intraspecific variation was different among the species. Taking into account intraspecific constancy of the major ISSR-PCR patterns and in the same time their susceptibility to individual differences we proposed these markers could be used to elucidate some complicated questions of bumble bee taxonomy.     

Characters of amino acid substitution in LDH-A and LDH-B in the evolutionary line of vertebrates

Structure of lactate dehydrogenase LDH-A (muscle) and LDH-B (heart) subunits is compared in the evolutionary line of vertebrates from Chondrosteous fishes to Mammals. It is revealed persistent differences between them in the amino acid set determining the physical and chemical characteristics of macromolecules. The polypeptide chain of LDH-A is shorter then that of LDH-B but it contains amino acids with higher molecular weight. In LDH-A polarized amino acids are less in number but charged amino acids are more numerous, positive charged amino acids prevail over negative charged ones. The features of polypeptide structure are discussed in connection with differences in the level of intraspecific variability of allozymes in the evolutionary line of vertebrates.     

Assessment of genetic polymorphism in Colorado potato beetle Leptinotarsa decemlineata 8Say) by RAPD markers

Four decanucleotide primers were chosen to detect polymorphism for randomly amplified polymorphic DNA (RAPD) in the populations of Colorado potato beetle. The variability of RAPD patterns was studied in three oblasts (Kiev, Moscow and Kurgan) that are geographically distant and considerably differ in ecological and climatic conditions affecting the development of this beetle: Kiev, Moscow, and Kurgan oblasts. A high level of intrapopulation polymorphism exceeding interpopulation differences was revealed. RAPD-marker subsets differing in the frequency and distribution throughout the studied populations were revealed.     

Individual polymorphism by RAPD markers in spring generation of the Colorado beetle Leptinotarsa decemlineata (Say)]

Genetic diversity of Colorado potato beetle in a natural population from Fastovskii rayon, Kiev oblast was estimated using RAPD. The level of polymorphism for RAPD markers was far higher in the spring generation than in the sample obtained from the same locality in summer of the preceding year. The frequency of individual RAPD markers was found to differ in males and females of potato beetle.     

Ester derivatives of nucleoside inhibitors of reverse transcriptase: I. Molecular transport systems for 3'-azido-3'-deoxythymidine and 2',3'-didehydro-3'-deoxythymidine

The methods of synthesis of the derivatives of nucleoside analogues esterified with various aliphatic, aromatic, and heteroaromatic acids and the construction from them of molecular transport systems that involve lipids, carbohydrates, peptides, and amino acids are discussed. The characteristics of the biological activity of a number of such systems are described.     

Ester derivatives of nucleoside inhibitors of reverse transcriptase: II. Molecular systems for combined therapy with 3'-azido-3'-deoxythymidine and 2',3'-didehydro-3'-deoxythymidine

The methods of synthesis of conjugates of anti-HIV nucleosides with various compounds, such as protease inhibitors, peptides, polysaccharides, and bicyclames, are considered; they are designated for the combined therapy of HIV.     

Evolution of rotifer population dynamics in a heterogeneous habitat: mathematical modeling

We present the results of mathematical modeling of a rotifer species inhabiting two coupled habitats with different environmental conditions. We use the modified Consensus model and show that the exchange between the habitats can lead to chaotization of originally regular plankton dynamics and synchronization of plankton biomass oscillations. As a result, the invasion of a chaotic regime takes place.