Calibration of measured center of pressure of a new stairway design for kinetic analysis of stair climbing

A stairway that allows the collection of kinetic data is essential for biomechanical studies on stair climbing. There is a need to validate the measured center of pressure (COP) on the surface of a stair in order to verify the accuracy of the calculation of joint kinetics. The purpose of this study was to validate a new stairway design for kinetic analysis of stair climbing through a calibration and error analysis of the COP obtained from this system. The new stairway design allows the collection of kinetic data for multiple steps without any constraint to foot placement. Known vertical forces were applied to known locations on the surface of each stair and each force plate. Multiple regression analyses were conduced to determine the distribution pattern of the error in the measured COP. It was found that the error in the COP was a function of location on the stair or force plate. The magnitude of the vertical force had no significant effect on the error in the measured COP. The distribution pattern of the error in the measured COP on the force plates used in this study matched the results in the literature. A healthy female subject was used as the subject in a stair climbing test. The error in the measured COP had a significant effect on the calculated joint resultant moments, especially the abduction-adduction and internal-external rotation moments. The correction of these errors should make the kinetic calculation in stair climbing more accurate.     

Metapopulations of moths on islands: a test of two contrasting models

1. We describe a generalized mainland-island metapopulation model which includes migration among the island populations. We test model predictions with quantitative data on more than 200 species of moths in two contrasting networks of small islands. The data include a direct measure of migration rate, based on trapping of moths on rocky skerries with no local populations of the vast majority of species.
2. We predicted that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, because the latter 'compete' for immigrants from the mainland. In contrast, we predicted that weakly flying species with potentially large local populations on the islands occur more frequently on islands in a group due to enhanced colonization rate.
3. Both predicted patterns were observed. Island occupancy increased significantly with the number of individuals caught on the rocky skerries, which is our measure of migration rate from the mainland, supporting the basic assumption that the species occur on the islands in a balance between colonizations and extinctions.
4. These results demonstrate that the moth metapopulations on islands represent a mixture of Levins's and mainland-island metapopulations, and that the mixture is different for different species in the same landscape.     

Statistical fluctuations in processes of gene expression regulation: consideration of the problem from point of view of statistical mechanics

The regulation of gene expression is a basic problem of biology. In some cases, the gene activity is regulated by specific binding of regulatory proteins to DNA. In terms of statistical mechanics, this binding is described as the process of adsorption of ligands on the one-dimensional lattice and has a probability nature. As a random physical process, the adsorption of regulatory proteins on DNA introduces a noise to the regulation of gene activity. We derived equations, which make it possible to estimate this noise in the case of the binding of the lac repressor to the operator and showed that these estimates correspond to experimental data. Many ligands are able to bind nonspecifically to DNA. Nonspecific binding is characterized by a lesser equilibrium constant but a greater number of binding sites on the DNA, as compared with specific binding. Relations are presented, which enable one to estimate the probability of the binding of a ligand on a specific site and on nonspecific sites on DNA. The competition between specific and nonspecific binding of regulatory proteins plays a great role in the regulation of gene activity. Similar to the one-dimensional "lattice gas" of particles, ligands adsorbed on DNA produce "one-dimensional" pressure on proteins located at the termini of free regions of DNA. This pressure, an analog of osmotic pressure, may be of importance in processes leading to changes in chromatin structure and activation of gene expression.     

Calculation of half-lives of proteins in vivo. Heterogeneity in the rate of degradation of yeast proteins

Summary A method is given for the calculation of half-lives of proteins in vivo from the measurement of the decrease of radioactivity in pulse-labelled proteins with time. This method could be particularly useful for the study of the degradation of proteins in cells that have a low growth rate.The method applied to growing yeast indicates that there are two major classes of protein. The class with low turnover constitutes the bulk of yeast protein and has a half-life of 160 h in a medium with glucose or galactose and of 50 h in a medium with ethanol. The class of proteins with high turnover (half-life between 0.8 and 2.4 hours) represents from 1% of total protein in yeast growing on glucose to 7% in yeast growing on ethanol.It is shown that some proteins which are derepressed during growth on ethanol or induced during growth on galactose are particularly susceptible to degradation in a medium which contains glucose.It is proposed that protein degradation is regulated by a coarse control at the level of protease activity and a fine control on the susceptibility of individual proteins to proteases.     

A Mechanism of Action of Neurotransmitters on the Regeneration of the Planarian Worm Dugesia tigrina. Role of Acetylcholine as a Negative Feed-back

By means of histochemical and pharmacological analysis it is shown that acetylcholine has an inhibitive effect on regeneration in the planaria Dugesia tigrina. It seems that serotonin and adrenaline on the one hand, and acetylcholine on the other hand, play a role in a mechanism of regulation in which the latter plays a role in a negative feed-back process.     

Reciprocal modulation of regulatory action of prolactin and somatotropin on DNA synthesis in granulosa cells of cows

A comparative analysis of the individual and joint influence of bovine prolactin (BPRL) and bovine somatotropin (BST) on DNA synthesis in cultured bovine granulosa cells from follicles of 3-5 mm in diameter was conducted, and a possibility for regulation of BPRL binding to receptors on the cells by BST was examined. Despite a unidirectional growth-promoting action of BPRL and BST on granulosa cells, their joint mitogenic effect on the cells was not additive at low concentrations of BPRL. The addition of BST to the culture medium did not alter the biphasic character of dependence of DNA synthesis in the cells on BPRL concentration, but increased the maximum effective concentration of the latter. When culturing granulosa cells with BST, the absence of its influence on the level of BPRL specific binding to the cells was shown. This fact suggests that BST modulating action on the mitogenic effect of BPRL is not a result of a change in the number of free receptors for PRL on granulosa cells. The results obtained are discussed in relation to the notion of similarity of receptor functional properties and intracellular signal ways for PRL and ST.     

Integration of the effects of estradiol and progesterone in the modulation of gonadotropin secretion

Estradiol secreted by the maturing follicle is the primary trigger for the surge of gonadotropins leading to ovulation. Progesterone has stimulatory or inhibitory actions on this estrogen-induced gonadotropin surge depending upon the time and dose of administration. The administration of progesterone to immature ovariectomized rats primed with a low dose of estradiol induced a well-defined LH surge and prolonged FSH release, a pattern similar to the proestrus surge of gonadotropins. A physiological role of progesterone is indicated in the normal ovulatory process because a single injection of the progesterone antagonist RU 486 on the day of proestrus in the adult cycling rat and on the day of the gonadotropin surge in the pregnant mare's serum gonadotropin stimulated immature rat resulted in an attenuated gonadotropin surge and reduced the number of ova per ovulating rat. Progesterone administration brought about a rapid LHRH release and an decrease in nuclear accumulation of estrogen receptors in the anterior pituitary but not the hypothalamus. The progesterone effect was demonstrated in vitro in the uterus and anterior pituitary and appears to be confined to occupied estradiol nuclear receptors. In in vivo experiments the progesterone effect on estradiol nuclear receptors appeared to be of approximately 2-h duration, which coincided with the time period of progesterone nuclear receptor accumulation after a single injection of progesterone. During the period of progesterone effects on nuclear estrogen receptors, the ability of estrogens to induce progesterone receptors was impaired. Based on the above results, a model is proposed for the stimulatory and inhibitory effects of progesterone on gonadotropin secretion.     

Effect of carbon sources upon the mycelial growth of Phytophthora citrophthora

In order to study the effect of carbon originating from different sources on the growth ofP. citrophthora, a modified Christie's formula was used as the basic nutrient medium. Carbon in various forms was then substituted for glucose in equivalent amounts. The fungus grew to a limited extent on glucose as the carbon source, but grew quite well on a maltose medium and less extensively on a sucrose medium. Fungus growth was most profuse on soluble starch, even more so than on potato dextrose and oatmeal medium. No sporangia were found in any of the media.     

Kinetic study of seita-fitting

We have already presented two studies of the traditional carrier frame, the seita. In our first study, we reported on seita users supporting loads not on the lumbar vertebrae but on the sacrum. In the second study, we showed that carrying a load on the sacrum was efficient in terms of metabolic rate, muscle activity, cadence and subjective responses. The purpose of this study was to verify the effect of carrying a load on the sacrum in terms of gait pattern. We compared the kinetic parameters produced while carrying a load on the sacrum (LOS) with those produced while carrying a load on the lumbar vertebrae (LOLV). Maximum propulsive force and medial impulse were significantly larger in LOS than in LOLV. These results suggested that a normal gait pattern was maintained more in LOS conditions than in LOLV conditions. This indicated that seita-fitting was efficient for carrying and transporting loads.     

Calculation of the number of samples needed to estimate the species richness of a taxocene

A formula to calculate the area of samples that would provide the necessary level of completeness for a species richness survey of a cenosis has been deduced. The model is based on a stochastic differential equation that describes random fluctuations in species abundance and on the assumption that a Poisson distribution of individuals in space occurs. The calculations are illustrated based on the example of the littoral polychaete taxocene in Vityaz Bay of Possiet Bay of the Sea of Japan.     

An iron-dependent mutant of Listeria monocytogenes of attenuated virulence

Abstract A bank of Tn 917 -insertional mutants from the facultative intracellular pathogen Listeria monocytogenes was screened by an original method based on bacterial growth on synthetic medium under iron-limiting conditions. One mutant, whose in vitro growth in synthetic medium was specifically dependent upon the availability of iron in its environment, was isolated and characterized. The insertional event occurred in a non-coding region, upstream of a rrn operon and located within a 1100-kb Not I fragment of the physical map, where the virulence genes already identified in L. monocytogenes were also present. Protein analysis by SDS-PAGE revealed a pleiotropic effect of the insertional event on cell-associated proteins, suggesting a polar effect of the transposon on adjacent unknown gene(s). The virulence in the mouse of this mutant was strongly impaired, although it was capable in vitro of growing intracellularly and of spreading from cell to cell, as shown by the production of lytic plaques on cell culture.     

Effect of histamine on duration of phases of the respiration cycle

Histamine produced either a bronchodilation or a bronchoconstriction in rats. In a 0.01-1.0 mcg/ml concentration histamine augmented the contractions amplitude in electrical stimulation of the trachea, in a 10-100 mcg/ml concentration histamine enhances the muscle tone thus decreasing the induced contractions. The histamine effects seems to be connected with its prevailing influence on different structures of the airways depending on the concentration. Its high concentrations act directly on the smooth muscle whereas its lower concentration affects receptors signaling the functional modules of the metasympathetic nervous system within the intramural ganglia of the trachea.     

Estimation of age and rate of increase of rare variants.

The problem considered is that of estimating the age or rate of increase of a variant on the basis of the present number of replicates observed in a population. In place of previous diffusion equation analyses of age probability distributions, the likelihood for the age is studied on the basis of a discrete branching process model. It is shown that variations inherent in the process of gene evolution in natural populations make it impossible to provide a reliable point estimate of the age of a specified variant, although the likelihood analysis provides a confidence interval which may place useful bounds on the period in which a variant originated. The observed distribution of numbers of several variants may also provide useful information. The problems of estimation are discussed with reference to rare variants arising in American Indian populations.     

The effect of electromagnetic waves of very high frequency of molecular spectra of radiation and absorption of nitric oxide on the functional activity of platelets

A study was made of the effect of electromagnetic EMI MMD-fluctuation on the frequencies of molecular spectra of radiation, and nitric oxide absorption under in vitro conditions on the functional activity of platelets in patients with unstable angina pectoris, with the help of a specially created generator. At amplitude-modulated and continuous modes of EMI MMD-irradiation of platelet-rich plasma for 5, 15 and 30 min the platelet functional activity decreases, which was shown up in reduction of their activation and fall of aggregative ability. The degree, to which platelet functional activity was inhibited, depended on the mode of irradiation and on duration of EMI MMD effect. The most obvious changes in platelet activation and in their readiness to aggregative response were observed at a continuous mode of irradiation within a 15 min interval.     

The spreading of monolayers of myosin

The spreading of the muscle proteins myosin and actomyosin depends both on the salt solution in which the proteins are dissolved and on the solution on which they are spread. The spreading is more complete the lower the concentration of the salt solution in which the proteins are dissolved and the higher the salt concentration of the solutions on which the proteins are spread. This effect seems to be due partially to the difference in density allowing the spread droplets a longer life on the surface, and partially to the effect of salt on the charge of the protein. A change in the pH of the substrate has a smaller effect than a change in the salt concentration. Heavy metals like Cu⁺⁺ or Zn⁺⁺, inhibit spreading almost completely. The dependence of spreading on these salts and on time was investigated in detail.The effect of the different salts was also compared with the effect of different phosphate compounds. It was noted that the above substances, including the different salts, phosphate compounds, and heavy metals, affect the mechanism of spreading but not films already spread. The viscosity of these fibrillar proteins was compared with other proteins in the monomolecular film state and in myosin an unusually high viscosity was found.     

In vitro movement of actin filaments on gizzard smooth muscle myosin: requirement of phosphorylation of myosin light chain and effects of tropomyosin and caldesmon

ATP-dependent movement of actin filaments on smooth muscle myosin was investigated by using the in vitro motility assay method in which myosin was fixed on the surface of a coverslip in a phosphorylated or an unphosphorylated state. Actin filaments slid on gizzard myosin phosphorylated with myosin light chain kinase (MLCK) at a rate of 0.35 micron/s, but did not slide at all on unphosphorylated myosin. The movement of actin filaments on phosphorylated myosin was stopped by perfusion of phosphatase. Subsequent perfusion with a solution containing MLCK, calmodulin, and Ca2+ enabled actin filaments to move again. The sliding velocities on monophosphorylated and diphosphorylated myosin by MLCK were not different. Actin filaments did not move on myosin phosphorylated with protein kinase C (PKC). The sliding velocity on myosin phosphorylated with both MLCK and PKC was identical to that on myosin phosphorylated only with MLCK. Gizzard tropomyosin enhanced the sliding velocity to 0.76 micron/s. Gizzard caldesmon decreased the sliding velocity with increase in its concentration. At a 5-fold molar ratio of caldesmon to actin, the movement stopped completely. This inhibitory effect of caldesmon was relieved upon addition of excess calmodulin and Ca2+.     

Characterization of a glycerol kinase mutant of Aspergillus niger

A glycerol-kinase-deficient mutant of Aspergillus niger was isolated. Genetic analysis revealed that the mutation is located on linkage group VI. The phenotype of this mutant differed from that of a glycerol kinase mutant of Aspergillus nidulans in its ability to utilize dihydroxyacetone (DHA). The weak growth on glycerol of the A. niger glycerol kinase mutant showed that glycerol phosphorylation is an important step in glycerol catabolism. The mutant could still grow normally on DHA because of the presence of a DHA kinase. This enzyme, probably in combination with an NAD(+)-dependent glycerol dehydrogenase, present only in the mutant, is responsible for the weak growth of the mutant on glycerol. Enzymic analysis of both the mutant and the parental strain showed that at least three different glycerol dehydrogenases were formed under different physiological conditions: the NAD(+)-dependent enzyme described above, a constitutive NADP(+)-dependent enzyme and a D-glyceraldehyde-specific enzyme induced on D-galacturonate. The glycerol kinase mutant showed impaired growth on D-galacturonate.     

Effects of laminin glycopeptides on metastasis—related behaviors of cancer cells

Our previous reports have shown that lamininglycopeptides (LN-GPs),the total glycopeptides prepared from laminin (LN),can prevent the experimental lung metastasis and liver metastasis of mouse cancer cells.In order to explore the anti-metastatic mechanism of LN-GPs,we studied the effects of LN-GPs on metastasisrelated behaviors of cancer cells in vitro.LN-GPs did not affect cell survival.However,LN-GPs inhibited cell attachment and spreading of S180 cells on LN-and Matrigelsubstrate in dose-dependent and time-dependent manners.Moreover,inhibition of cell attachment and spreading on Matrigel substrates were much greater on Matrigel substrate than on LN substrate.In the gresence of LN-GPs,S180 cells on LN substrate changed from a flattened polygonal shape to a round one,the migration of S180 cells on LN substrate decreased,and the number of a highly invasive human pulmonary giant carcinoma PG cells invading Matrigel filter in a Boyden chamber was reduced.LN-GPs thus have multiple inhibitory effects on cancer metastasisrelated behaviors.