Interactions of divalent cations with single calcium channels from rat brain synaptosomes

Voltage-dependent calcium channels from a rat brain membrane preparation ("synaptosomes") were incorporated into planar lipid bilayers. The effects of calcium, barium, strontium, manganese, and cadmium ions on the amplitudes and kinetics of single channel currents were examined. The order of single channel conductances was gBa greater than gSr greater than gMn, which was the inverse of the order of the mean channel open times: TMn greater than TCa = TSr greater than TBa. In contrast, the identity of the charge carrier had little or no effect on the mean closed times of the channel. Manganese, in the absence of other permeant ions, can pass through single channels (gMn = 4 pS). However, when added to a solution that contained another type of permeant divalent cation, manganese reduced the single channel current in a voltage-dependent manner. Cadmium, a potent blocker of macroscopic "ensemble" calcium currents in many preparations, reduced the current through an open channel in a manner consistent with Cd ions both not being measurably permeant and interacting with a single site. The permeant ions competed with cadmium for this site with the following order: Mn greater than Sr = Ca greater than Ba. These results are consistent with the existence of no less than one divalent cation binding site in the channel that regulates ion permeation.     

Isocitrate Lyase from Germinating Soybean Cotyledons: Purification and Characterization

Ruchti, M. and Widmer, F. 1986. Isocitrate lyase from germinatingsoybean cotyledons: purification and characterization.—J.exp. Bot. 37: 1685–1690. Isocitrate lyase (E.C. 4.1.3.1 [EC] ) was purified from the cotyledonsof 7-d-old soybean seedlings. Three molecular forms were detectedwith pi values of 6·46, 6·25 and 6·0. Themain form (pl = 6·46) had an approximate Mr of 130000,a pH optimum of 8·0, a K_m (isocitrate) close to 2·0mol m^–3 and a molecular activity of 615 min ^–1 at25 °C. The purified enzyme is not a glycoprotein and isheat labile. Key words: Isocitrate lyase, soybean     

Pandinus imperator scorpion venom blocks voltage-gated potassium channels in GH3 cells

We examined the effects of Pandinus imperator scorpion venom on voltage-gated potassium channels in cultured clonal rat anterior pituitary cells (GH3 cells) using the gigohm-seal voltage-clamp method in the whole-cell configuration. We found that Pandinus venom blocks the voltage-gated potassium channels of GH3 cells in a voltage-dependent and dose-dependent manner. Crude venom in concentrations of 50-500 micrograms/ml produced 50-70% block of potassium currents measured at -20 mV, compared with 25-60% block measured at +50 mV. The venom both decreased the peak potassium current and shifted the voltage dependence of potassium current activation to more positive potentials. Pandinus venom affected potassium channel kinetics by slowing channel opening, speeding deactivation slightly, and increasing inactivation rates. Potassium currents in cells exposed to Pandinus venom did not recover control amplitudes or kinetics even after 20-40 min of washing with venom-free solution. The concentration dependence of crude venom block indicates that the toxins it contains are effective in the nanomolar range of concentrations. The effects of Pandinus venom were mimicked by zinc at concentrations less than or equal to 0.2 mM. Block of potassium current by zinc was voltage dependent and resembled Pandinus venom block, except that block by zinc was rapidly reversible. Since zinc is found in crude Pandinus venom, it could be important in the interaction of the venom with the potassium channel. We conclude that Pandinus venom contains toxins that bind tightly to voltage-dependent potassium channels in GH3 cells. Because of its high affinity for voltage-gated potassium channels and its irreversibility, Pandinus venom may be useful in the isolation, mapping, and characterization of voltage-gated potassium channels.     

Effects of Increasing Water Stress on Simulated Swards of Festuca arundinacea Schreb under Wind Tunnel Conditions

The effects of increasing water stress on water relations, leafconductance, leaf extension and leaf rolling of Festuca arundinaceain sward (I m²) were investigated under wind tunnel conditions.The plants were grown in a container 60 cm deep and the experimentwas conducted over a 36 d period. Upon cessation of watering(day 11), leaf extension and conductance were affected. Within8 d, the onset of leaf rolling helped to reduce transpirationand to maintain leaf water potential. Nocturnal recovery of turgor potential helped in maintainingleaf extension at a moderate level and in the final 5 d waterand osmotic potentials dropped sharply as leaf rolling becamemore acute and leaf extension stopped. The grass combines various morphological and physiological mechanismsto prevent water losses and maintain growth. Festuca arundinacea, tall fescue, wind tunnel, water stress, water potential, osmotic potential, conductance, leaf rolling, leaf extension     

Cerebellar neurones: Differentiation and modulation of sensitivity to excitotoxic treatment

The neurite outgrowth and adhesion complex (NOAC), isolated from rabbit sera has been dissociated in its major components by reverse-phase chromatography in HPLC by using a C₁₈ column. SDS-PAGE analisys of the active fractions revealed the presence of three major bands of approximately 100, 70 and 50 kDa. Studies on the biological activity of NOAC were carried out on rat cerebellar granule cells. NOAC-cultured cells exhibit a marked resistance to excitotoxic stimuli carried by glutamate.     

Organisation spatiale des fibres de collagène de la plaque basale des écailles des Téléostéens

Spatial organization of collagenous fibrils in the basal plate of elasmoid scales has been studied in 36 species among 24 teleost families which include the whole order. Angle measurements of the various fibrillary directions were performed on fracture surfaces in frozen scales observed with the scanning electron microscope. The organization of the basal plate is arrayed in three basic patterns. The most remarkable one, found in the more "primitive" families, is a double twisted plywood with a left-handed rotation of the fibrillary directions. The remaining two are an orthogonal plywood, more or less regular, and an "intermediate" plywood, both found among the more "advanced" families. However, an orthogonal plywood is also observed in some "primitive" families, for example in Clupeidae and Salmonidae. We tentatively interpret the left-handed double twisted plywood of the lower teleosteans and of Amiidae as a synapomorphy in relation to the primitive condition of an actinopterygian lineage. On the other hand, within the teleosts, we would consider that the double twisted plywood is a plesiomorphic condition and that the orthogonal plywood is an apomorphy among the "advanced" teleosts families.     

Molecular evolution of chloroplast DNA sequences

Comparative data on the evolution of chloroplast genes are reviewed. The chloroplast genome has maintained a similar structural organization over most plant taxa so far examined. Comparisons of nucleotide sequence divergence among chloroplast genes reveals marked similarity across the plant kingdom and beyond to the cyanobacteria (blue-green algae). Estimates of rates of nucleotide substitution indicate a synonymous rate of 1.1 x 10(-9) substitutions per site per year. Noncoding regions also appear to be constrained in their evolution, although addition/deletion events are common. There have also been evolutionary changes in the distribution of introns in chloroplast encoded genes. Relative to mammalian mitochondrial DNA, the chloroplast genome evolves at a conservative rate.      

High nucleotide sequence variation in a region of low recombination in Drosophila simulans is consistent with the background selection model

We surveyed nucleotide sequence variation at glucose dehydrogenase (Gld), in a region of low recombination on chromosome 3R, from a population sample of Drosophila simulans. The levels of nucleotide variation were surprisingly high. There was no departure from the expectation of a neutral model for the level of polymorphism, indicating no evidence of a selective sweep in this region. There was a significant deficiency of singleton polymorphisms according to the Fu and Li test, although Tajima and Hudson, Kreitman, and Aguade (HKA) tests do not provide evidence of a significant elevation of variation due to balancing selection. Genetic map data for the D. simulans third chromosome were used to calculate expected values of pi for Gld under a current model of background selection, varying the values for the parameter sh (selection coefficient against deleterious mutations). We show that the recombinational landscape of D. simulans is sufficiently different from that of D. melanogaster that we expect higher variation under the background selection model, even when effective population sizes are assumed to be equal. The data for Gld were tested against the predictions using computer simulations of the distribution of the number of segregating sites conditioned on pi. Background selection alone can explain our observations as long as sh is larger than 0.005 and species-level effective population size is assumed to be several- fold larger than in D. melanogaster. Alternatively, the deleterious mutation rate may be smaller in D. simulans, or balancing selection may be acting nearby, thereby reducing the effect of background selection.      

Comparative evolutionary analysis of rDNA ITS regions in Drosophila

The internal transcribed spacer (ITS) of the ribosomal DNA is generally considered to be under low functional constraint, and it is therefore often treated as a typical nonfunctional spacer sequence. We have analyzed the ITS regions of five species from the Drosophila melanogaster subgroup, two Drosophila species from outside this group (D. pseudoobscura and D. virilis), as well as from the more distantly related dipteran fly Musca domestica. The sequence comparisons show a distinctive conservation/divergence pattern, indicating that some regions are more conserved than others. Moreover, secondary-structure calculations indicate several conserved structural elements within the ITS regions. On the other hand, a statistical test that allows us to estimate the fraction of sites that are not under selective constraint suggests that more than half of the spacer is apparently free to diverge and evolves with a rate that is close to the neutral rate of sequence evolution in Drosophila. The ITS sequences can be used to derive a molecular phylogeny for the species under study. We find that the ITS tree is largely in line with the so-far-known phylogeny of this group of species, with one difference. The species most distant within the D. melanogaster subgroup is D. yakuba, rather than D. orena, as is normally assumed.