Kinetic basis for insensitivity to tetrodotoxin and saxitoxin in sodium channels of canine heart and denervated rat skeletal muscle

The single-channel blocking kinetics of tetrodotoxin (TTX), saxitoxin (STX), and several STX derivatives were measured for various Na-channel subtypes incorporated into planar lipid bilayers in the presence of batrachotoxin. The subtypes studied include Na channels from rat skeletal muscle and rat brain, which have high affinity for TTX/STX, and Na channels from denervated rat skeletal muscle and canine heart, which have about 20-60-fold lower affinity for these toxins at 22 degrees C. The equilibrium dissociation constant of toxin binding is an exponential function of voltage (e-fold per 40 mV) in the range of -60 to +60 mV. This voltage dependence is similar for all channel subtypes and toxins, indicating that this property is a conserved feature of channel function for batrachotoxin-activated channels. The decrease in binding affinity for TTX and STX in low-affinity subtypes is due to a 3-9-fold decrease in the association rate constant and a 4-8-fold increase in the dissociation rate constant. For a series of STX derivatives, the association rate constant for toxin binding is approximately an exponential function of net toxin charge in membranes of neutral lipids, implying that there is a negative surface potential due to fixed negative charges in the vicinity of the toxin receptor. The magnitude of this surface potential (-35 to -43 mV at 0.2 M NaCl) is similar for both high- and low-affinity subtypes, suggesting that the lower association rate of toxin binding to toxin-insensitive subtypes is not due to decreased surface charge but rather to a slower protein conformational step. The increased rates of toxin dissociation from insensitive subtypes can be attributed to the loss of a few specific bonding interactions in the binding site such as loss of a hydrogen bond with the N-1 hydroxyl group of neosaxitoxin, which contributes about 1 kcal/mol of intrinsic binding energy.     

Acute and chronic effects of insulin on lactate dehydrogenase (LDH) activity in tissues of albino rat (Wistar strain)

Male albino rats were treated with insulin for one week (acute) and four weeks (chronic). The lactate dehydrogenase (LDH) activity, lactate and pyruvate levels were estimated in the tissues of experimental and control animals. LDH activity decreased in all the tissues of acute- and chronic treated animals whereas the lactate content is elevated. Pyruvate content also showed increment except in heart and pancreas with reference to acute treatment where it is decreased. The hyperinsulinaemia effect in relation to lacticacidaemia and its influence on energy demand and ammonia secretion is discussed.     

Attenuation of visible light by phytoplankton in a vertically structured ocean: solutions and applications

To find the solution to problems in applied marine optics, wedo not always need to compute the submarine irradiance at alldepths; in many cases, it is sufficient to know the averageattenuation of light for finite layers of arbitrary thickness.If multiple scattering can be neglected, the average attenuationof light in a finite layer of the water column depends onlyon the vertical distribution of the attenuating substances;in open-ocean waters, the most important of these is phytoplankton.It is shown how the average attenuation of monochromatic lightin an arbitrary layer can be determined when the vertical pigmentprofile takes one of two standardized forms: a shifted Gaussianor a triangle. The choice of efficient algorithms to computethe attenuation in a layer using these models is discussed.The extension to polychromatic light involves the selectionof a function to represent the spectral distribution of thespecific absorption coefficient for phytoplankton, as determinedby observation. Chebyshev polynomial representation is shownto be convenient for applications which require the calculationof a weighted wavelength integral. An efficient procedure forthe evaluation of these integrals, Gauss-Chebyshev quadrature,is presented and evaluated. The extension to the computationof bulk properties for discrete layers is straightforward.     

Occurrence of a Lysogenic Streptomyces sp. on the Nodule Surface of Black Gram (Vigna mungo (L.) Hepper)

A lysogenic Streptomyces sp., strain NS.A4, which was isolated from the nodule surface of black gram (Vigna mungo (L.) Hepper), was found to inhibit rhizobia of fast-and slow-growing strains of cowpeas and soybeans. It exhibited plaques when there was a change in cultural conditions. Repeated culturing of the organism in nutrient agar and broth confirmed the infection of Streptomyces sp. strain NS.A4 by an actinophage. Addition of the culture filtrate of Streptomyces sp. strain NS.A4 to shaken broth cultures of three other Streptomyces spp. resulted in phage infection.     

Divalent cation selectivity for external block of voltage-dependent Na+ channels prolonged by batrachotoxin. Zn2+ induces discrete substates in cardiac Na+ channels

The mechanism of block of voltage-dependent Na+ channels by extracellular divalent cations was investigated in a quantitative comparison of two distinct Na+ channel subtypes incorporated into planar bilayers in the presence of batrachotoxin. External Ca2+ and other divalent cations induced a fast voltage-dependent block observed as a reduction in unitary current for tetrodotoxin-sensitive Na+ channels of rat skeletal muscle and tetrodotoxin-insensitive Na+ channels of canine heart ventricular muscle. Using a simple model of voltage-dependent binding to a single site, these two distinct Na+ channel subtypes exhibited virtually the same affinity and voltage dependence for fast block by Ca2+ and a number of other divalent cations. This group of divalent cations exhibited an affinity sequence of Co congruent to Ni greater than Mn greater than Ca greater than Mg greater than Sr greater than Ba, following an inverse correlation between binding affinity and ionic radius. The voltage dependence of fast Ca2+ block was essentially independent of CaCl2 concentration; however, at constant voltage the Ca2+ concentration dependence of fast block deviated from a Langmuir isotherm in the manner expected for an effect of negative surface charge. Titration curves for fast Ca2+ block were fit to a simplified model based on a single Ca2+ binding site and the Gouy-Chapman theory of surface charge. This model gave similar estimates of negative surface charge density in the vicinity of the Ca2+ blocking site for muscle and heart Na+ channels. In contrast to other divalent cations listed above, Cd2+ and Zn2+ are more potent blockers of heart Na+ channels than muscle Na+ channels. Cd2+ induced a fast, voltage-dependent block in both Na+ channel subtypes with a 46-fold higher affinity at 0 mV for heart (KB = 0.37 mM) vs. muscle (KB = 17 mM). Zn2+ induced a fast, voltage-dependent block of muscle Na+ channels with low affinity (KB = 7.5 mM at 0 mV). In contrast, micromolar Zn2+ induced brief closures of heart Na+ channels that were resolved as discrete substate events at the single-channel level with an apparent blocking affinity of KB = 0.067 mM at 0 mV, or 110-fold higher affinity for Zn2+ compared with the muscle channel. High-affinity block of the heart channel by Cd2+ and Zn2+ exhibited approximately the same voltage dependence (e-fold per 60 mV) as low affinity block of the muscle subtype (e-fold per 54 mV), suggesting that the block occurs at structurally analogous sites in the two Na+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Influence of Nutrient Availability and Quorum Sensing on the Formation of Metabolically Inactive Microcolonies Within Structurally Heterogeneous Bacterial Biofilms: An Individual-Based 3D Cellular Automata Model

The resistance of bacterial biofilms to antibiotic treatment has been attributed to the emergence of structurally heterogeneous microenvironments containing metabolically inactive cell populations. In this study, we use a three-dimensional individual-based cellular automata model to investigate the influence of nutrient availability and quorum sensing on microbial heterogeneity in growing biofilms. Mature biofilms exhibited at least three structurally distinct strata: a high-volume, homogeneous region sandwiched between two compact sections of high heterogeneity. Cell death occurred preferentially in layers in close proximity to the substratum, resulting in increased heterogeneity in this section of the biofilm; the thickness and heterogeneity of this lowermost layer increased with time, ultimately leading to sloughing. The model predicted the formation of metabolically dormant cellular microniches embedded within faster-growing cell clusters. Biofilms utilizing quorum sensing were more heterogeneous compared to their non-quorum sensing counterparts, and resisted sloughing, featuring a cell-devoid layer of EPS atop the substratum upon which the remainder of the biofilm developed. Overall, our study provides a computational framework to analyze metabolic diversity and heterogeneity of biofilm-associated microorganisms and may pave the way toward gaining further insights into the biophysical mechanisms of antibiotic resistance.     

Mapping QTLs for 15 morpho-metric traits in Arabidopsis thaliana using Col-0 × Don-0 population

Genome wide quantitative trait loci (QTL) mapping was conducted in Arabidopsis thaliana using F2 mapping population (Col-0 × Don-0) and SNPs markers. A total of five linkage groups were obtained with number of SNPs varying from 45 to 59 per linkage group. The composite interval mapping detected a total of 36 QTLs for 15 traits and the number of QTLs ranged from one (root length, root dry biomass, cauline leaf width, number of internodes and internode distance) to seven (for bolting days). The range of phenotypic variance explained (PVE) and logarithm of the odds ratio of these 36 QTLs was found be 0.19–38.17% and 3.0–6.26 respectively. Further, the epistatic interaction detected one main effect QTL and four epistatic QTLs. Five major QTLs viz. Qbd.nbri.4.3, Qfd.nbri.4.2, Qrdm.nbri.5.1, Qncl.nbri.2.2, Qtd.nbri.4.1 with PVE > 15.0% might be useful for fine mapping to identify genes associated with respective traits, and also for development of specialized population through marker assisted selection. The identification of additive and dominant effect QTLs and desirable alleles of each of above mentioned traits would also be important for future research.     

Role of Arabidopsis BBX proteins in light signaling

Journal of Plant Biochemistry and Biotechnology - Light regulates numerous aspects of plant growth and development like seed germination, seedling de-etiolation, pigment accumulation, cotyledon...