Random walk analysis of restricted metabolite diffusion in skeletal myofibril systems

The purpose of this work was the development of a basal mathematical model for the diffusion of low-molecular metabolites in a skeletal muscle cell. A three-dimension diffusion of low-molecular particles was simulated by a Monte-Carlo method (random walks of diffusing molecules). The model takes into account the following structural elements: (i) a regular lattice of actin and myosin filaments inside a myofibril; (ii) the membranes of sarcoplasmic reticulum and mitochondria surrounding the myofibrils; (iii) a set of myofibrils inside a skeletal muscle cell. We simulated diffusion of particles in the bulk of intracellular water phase and their reflections from the rigid surfaces of intracellular structures. The model allowed to calculate the apparent coefficients of particle diffusion in the axial and radial directions, Dparallel(app) and Dperpendicular(app), respectively. In accordance with experimental data from literature, the coefficient Dparallel(app) was independent of time. The coefficient of radial diffusion Dperpendicular(app) decreased with time to steady state values similar to that determined by the NMR diffusion spectroscopy methods. The interactions of diffusing particles with thin and thick filaments of myofibrils could explain the decrease in the Dperpendicular(app) value by a factor of 20%. The collisions of particles with myofilaments began to reveal themselves as a gradual decrease in the Dperpendicular(app) value at early stages of diffusion (t1/2 approximately equal to 0.05 microsec). The contribution of particle reflections from the membranes of sarcoplasmic reticulum and mitochondria to the retardation of the radial diffusion was about of 20-30%, depending on porosity of a membranous shield around the myofibril. For conventional sizes of a membranous shield (diameter 2 microm), the interactions of particles with the shield caused a decrease in the Dperpendicular(app) value with a half-time t1/2 approximately equal to 0.5 msec. This time is essentially lower by a factor about of 100 than that found in published NMR measurements. When we considered diffusion of particles inside a cell compartment confined to impermeable membranous shield, the reflection of particles from this shield led the drastic decrease in the radial diffusion coefficient (Dperpendicular(app) --> porportional to when t --> porportional to). This pattern of the Dperpendicular(app)(t) time-course might be expected in the NMR measurements on skeletal muscle tissue where a sarcolemma represents an impermeable shield for ATP and PCr molecules.     

Out of Africa and back again: nested cladistic analysis of human Y chromosome variation

We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544 individuals from Africa, Asia, Europe, Oceania, and the New World. Phylogenetic analyses of these nine sites resulted in a tree for 10 distinct Y haplotypes with a coalescence time of approximately 150,000 years. The 10 haplotypes were unevenly distributed among human populations: 5 were restricted to a particular continent, 2 were shared between Africa and Europe, 1 was present only in the Old World, and 2 were found in all geographic regions surveyed. The ancestral haplotype was limited to African populations. Random permutation procedures revealed statistically significant patterns of geographical structuring of this paternal genetic variation. The results of a nested cladistic analysis indicated that these geographical associations arose through a combination of processes, including restricted, recurrent gene flow (isolation by distance) and range expansions. We inferred that one of the oldest events in the nested cladistic analysis was a range expansion out of Africa which resulted in the complete replacement of Y chromosomes throughout the Old World, a finding consistent with many versions of the Out of Africa Replacement Model. A second and more recent range expansion brought Asian Y chromosomes back to Africa without replacing the indigenous African male gene pool. Thus, the previously observed high levels of Y chromosomal genetic diversity in Africa may be due in part to bidirectional population movements. Finally, a comparison of our results with those from nested cladistic analyses of human mtDNA and beta-globin data revealed different patterns of inferences for males and females concerning the relative roles of population history (range expansions) and population structure (recurrent gene flow), thereby adding a new sex-specific component to models of human evolution.      

In vivo and in vitro assessment of brain bioenergetics in aging rats

Brain energy disorders can be present in aged men and animals. To this respect, the mitochondrial and free radical theory of aging postulates that age‐associated brain energy disorders are caused by an imbalance between pro‐ and anti‐oxidants that can result in oxidative stress. Our study was designed to investigate brain energy metabolism and the activity of endogenous antioxidants during their lifespan in male Wistar rats. In vivo brain bioenergetics were measured using ³¹P nuclear magnetic resonance (NMR) spectroscopy and in vitro by polarographic analysis of mitochondrial oxidative phosphorylation. When compared to the young controls, a significant decrease of age‐dependent mitochondrial respiration and adenosine‐3‐phosphate (ATP) production measured in vitro correlated with significant reduction of forward creatine kinase reaction (kfor) and with an increase in phosphocreatine (PCr)/ATP, PCr/Pi and PME/ATP ratio measured in vivo. The levels of enzymatic antioxidants catalase, GPx and GST significantly decreased in the brain tissue as well as in the peripheral blood of aged rats. We suppose that mitochondrial dysfunction and oxidative inactivation of endogenous enzymes may participate in age‐related disorders of brain energy metabolism.     

Aerobic training increases the expression of adiponectin receptor genes in the peripheral blood mononuclear cells of young men

Little is known about the effect of exercise training on the expression of adiponectin receptor genes in peripheral blood mononuclear cells (PBMCs). In this study, we investigated the effects of aerobic training on the expression of AdipoR1 and AidpoR2 mRNAs in PBMCs, whole body insulin sensitivity, and circulating adiponectins in men. Thirty young men were randomly assigned to either a control (n=15) or an exercise (n=15) group. Subjects assigned to the exercise group underwent a 12-week jogging and/or running programme on a motor-driven treadmill at an intensity of 60%-75% of the age-based maximum heart rate with duration of 40 minutes per session and a frequency of 5 days per week. Two-way mixed ANOVA with repeated measures was used to test any significant time-by-group interaction effects for the measured variables at p=0.05. We found significant time-by-group interaction effects for waist circumference (p=0.001), VO_2max (p<0.001), fasting insulin (p=0.016), homeostasis model assessment for insulin resistance (HOMA-IR) (p=0.010), area under the curve (AUC) for insulin response during the 75-g oral glucose tolerance test (p=0.002), high-molecular weight (HMW) adiponectin (p=0.016), and the PBMC mRNA levels of AdipoR1 (p<0.001) and AdipoR2 (p=0.001). The exercise group had significantly increased mRNA levels of AdipoR1 and AdipoR2 in PBMCs, along with increased whole body insulin sensitivity and HMW adiponectin, decreased waist circumference, and increased VO_2max compared with the control group. In summary, the current findings suggest that exercise training modulates the expression of AdipoR1 and AdipoR2 mRNAs in PBMCs, implying that manipulation of the expression of these genes could be a potential surrogate for lifestyle intervention-mediated improvements of whole body insulin sensitivity and glucose homeostasis.     

Biochip detection of KRAS,BRAF, and PIK3CA somatic mutations in colorectal cancer patients

Molecular Biology - Somatic mutations of KRAS, PIK3CA, and BRAF cause insensitivity of colorectal tumors to therapy with anti-EGFR monoclonal antibodies, necessitating a genetic testing prior to...     

Respiratory responses to microinjections of gastrin-releasing peptide into the solitary tract nucleus

In acute experiments on urethane-anesthetized rats, the respiratory effects ofmicroinjections of 10(-5), 10(-8) and 10(-10) M gastrin-releasing peptide (GRP) into the solitary tract nucleus were investigated. It was found that microinjections of the neuropeptide induced an increase in tidal volume, amplitude of diaphragm and external intercostal muscles firing activity and in expiratory duration. The most obvious respiratory responses observed when 10(-8) M GRP was used, while 10(-10) M GRP appeared to be sub-threshold and didn't alter the breathing pattern and activity of inspiratory muscles. In some experiments, where the blood pressure and the heart rate was monitored alone with breathing pattern, these parameters did not change after GRP microinjections into the solitary tract nucleus. The obtained data together with particularities of the distribution of GRP receptors in the brainstem suggest the possibility of GRP involvement into the respiratory control mechanisms at the level of solitary tract nucleus.