Study of the interaction between rabbit cardiac contractile and regulatory proteins. An <Emphasis Type="Italic">in vitro</Emphasis> motility assay

A series of experiments was performed in an in vitro motility assay with reconstructed thin filaments to obtain pCa-force relationships for cardiac isomyosins V1 and V3. Two concentrations of each isomyosin (200 and 300 microg/ml) on the surface of a flow cell were tested. Isometric force was estimated as the amount of actin-binding protein, alpha-actinin, stopping thin filament movement. It was found that the amount of alpha-actinin stopping the movement at saturating calcium concentration for V3 was twice higher than for V1 at both concentrations of isoforms. Hill coefficients of cooperativity (h) were determined for pCa-force relationships. The value of h did not differ significantly for isoforms at 300 microg/ml of protein (h was 1.56 for V1 and 1.54 for V3). However, the Hill coefficient was higher for V3 isoform at 200 microg/ml (h = 2.00 and 1.76 for V3 and V1, respectively). Importantly, the Hill coefficient increased for both isoenzymes when their concentrations were decreased. The connection between Hill coefficient and cooperative interactions between cardiac contractile and regulatory proteins is analyzed in detail.     

Biometric variations and oxidative stress responses in juvenile Clarias gariepinus exposed to Termex®

The current study investigated the effects of termite insecticide, Termex® (imidacloprid 35.50% SC), on biometric variations and oxidative stress biomarkers in Clarias gariepinus. Fish were exposed to 4.00 and 6.00 µg l^–1 sublethal Termex® concentrations in 2017. The gill and liver tissues were sampled on days 7, 14, 21 and 28 and the results indicated that hepatosomatic index (HSI) decreased significantly when compared with the control on days 14, 21 and 28. The condition factor (CF) and viscera-somatic index (VSI) also decreased during the study period. The decrease was greater at 6.00 µg l^–1 Termex® concentration on days 21 and 28 for CF and days 14 to 28 for VSI, respectively. The lipid peroxidation (LPO) in both tissues was highest in the 6.00 µg l^?1 Termex® and increased with the duration. There was significant decrease (p < 0.05) in superoxide dismutase and glutathione peroxidase values, but significant increase in catalase activity in both tissues. The values of glutathione reductase in both tissues were comparable to the control, except on days 21 and 28 in the liver. There was negative correlation between the LPO in tissues and the HSI, CF and VSI values. The use of Termex® in the environment should be monitored to safeguard the health of aquatic organisms.     

Why Muscle is an Efficient Shock Absorber

Skeletal muscles power body movement by converting free energy of ATP hydrolysis into mechanical work. During the landing phase of running or jumping some activated skeletal muscles are subjected to stretch. Upon stretch they absorb body energy quickly and effectively thus protecting joints and bones from impact damage. This is achieved because during lengthening, skeletal muscle bears higher force and has higher instantaneous stiffness than during isometric contraction, and yet consumes very little ATP. We wish to understand how the actomyosin molecules change their structure and interaction to implement these physiologically useful mechanical and thermodynamical properties. We monitored changes in the low angle x-ray diffraction pattern of rabbit skeletal muscle fibers during ramp stretch compared to those during isometric contraction at physiological temperature using synchrotron radiation. The intensities of the off-meridional layer lines and fine interference structure of the meridional M3 myosin x-ray reflection were resolved. Mechanical and structural data show that upon stretch the fraction of actin-bound myosin heads is higher than during isometric contraction. On the other hand, the intensities of the actin layer lines are lower than during isometric contraction. Taken together, these results suggest that during stretch, a significant fraction of actin-bound heads is bound non-stereo-specifically, i.e. they are disordered azimuthally although stiff axially. As the strong or stereo-specific myosin binding to actin is necessary for actin activation of the myosin ATPase, this finding explains the low metabolic cost of energy absorption by muscle during the landing phase of locomotion.     

Study of reciprocal effects of cardiac myosin and tropomyosin isoforms on actin-myosin interaction with in vitro motility assay

Interaction of myosin with actin in striated muscle is controlled by Ca²⁺ via thin filament associated proteins: troponin and tropomyosin. In cardiac muscle there is a whole pattern of myosin and tropomyosin isoforms. The aim of the current work is to study regulatory effect of tropomyosin on sliding velocity of actin filaments in the in vitro motility assay over cardiac isomyosins. It was found that tropomyosins of different content of α- and β-chains being added to actin filament effects the sliding velocity of filaments in different ways. On the other hand the velocity of filaments with the same tropomyosins depends on both heavy and light chains isoforms of cardiac myosin.     

Characterization of chaotic dynamics in the human menstrual cycle

Background  

The human menstrual cycle is known to exhibit a significant amount of unexplained variability. This variation is typically dismissed as random fluctuations in an otherwise periodic and predictable system. Given the many delayed nonlinear feedbacks in the multiple levels of the reproductive endocrine system, however, the menstrual cycle can properly be construed as the output of a nonlinear dynamical system, and such a system has the possibility of being in a chaotic trajectory. We hypothesize that this is in fact the case and that it accounts for the observed variability.     

Application of Fractal Analysis to Evaluate the Rat Brain Arterial System

Biophysics - Vascular networks possess properties of self-similarity, which allows one to consider them as stochastic fractals. The box-counting method based on calculations along the vessel...     

The effect of glyprolines on stressogenic disorders in the rat behaviour

Protective and antistress effects of three glyprolines--PGP, PG and GP, were studied. Stress influences produced typical changes of behavioural activity of rats in the elevated pluz-maze and the hole-board tests. These changes suggest a significant enhancement of anxiety and a drop of the level of orientation-investigative activity. A preliminary (15 minutes before stress agent) intraperitoneal administration of PGP or GP in doses of 3.7 microm/kg significantly decreased stress disturbances of behaviour. Analysis of these data shows to the possibility of PGP and GP influences on the CNS structures, which take part in the organism reciprocal reactions to stress factor. The peptide GP at equimolar dose didn't possess pronounced protective properties and just slightly decreased stress disturbance of behavioural activity of rats.     

Sequence analysis of the ribosomal DNA internal transcribed spacer 2 from populations of Anopheles nuneztovari (Diptera: Culicidae)

Sequence variation of the ribosomal DNA internal transcribed spacer 2 (ITS2) was examined for populations of the malaria vector Anopheles nuneztovari collected in Colombia, Venezuela, Bolivia, Suriname, and Brazil. Mosquitoes from Colombia and Venezuela had identical ITS2 sequences and were distinguished from sequences in other populations by three insertion/deletion events (indels) and by one transversion. The length of the ITS2 was 363-369 bp, and it had a G+C content of 55.3%- 55.7%. Variation in the length of the ITS2 between and within populations was due to indels in simple repeats. ITS2 consensus sequences were similar or identical for samples from the following three groups: (1) Colombia, Bolivia, and Venezuela; (2) Suriname and northern Brazil; and (3) eastern and central Brazil. The presence of two different consensus sequences from a single location near Manaus, Brazil, suggests that populations from eastern Brazil and those from Suriname converge in this region of the Amazon Basin. These data show that putative cryptic species of An. nuneztovari are distinguished by very minor differences in DNA sequence of the ITS2 region.