Parallel measurements of bound calcium and force in glycerinated rabbit psoas muscle fibers

A simple double-isotope procedure has been developed for making simultaneous measurements of bound Ca²⁺ and relative force in glycerinated rabbit psoas bundles containing two fibers. With this preparation it is possible to study Ca²⁺-troponin interactions coincident with MgATP-induced force development. Over the free [Ca²⁺] range 6 · 10^?8–1.2 · 10^?5 M the bound Ca²⁺ varied from 0.25 to 1.65 μmol/g protein. The free [Ca²⁺] at half-maximal Ca²⁺ saturation was 2 · 10^?7 M while that a half-maximal force was 5 · 10^?7 M. Half-maximal Ca²⁺ saturation was associated with 20% maximal force. The force-[Ca²⁺] saturation curve showed a steep rise in slope at greater than half saturation. The observed relationship was consistent with a model in which multiple occupancy of troponin Ca²⁺-binding sites is essential for initiation of cross-bridge cycling.     

Relationship of Heliothis zea predators, parasitoids and entomopathogens to canopy development in soybean as affected by Heterodera glycines and weeds

The influence of canopy development in soybean on the survival of corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), egg and larval stages and population dynamics of arthropod fauna were evaluated in field trials during 1986–88 in eastern North Carolina. Soybean canopy size decreased as soybean cyst nematode, Heterodera glycines Ichinohe (Nematoda: Heteroderidae), initial population densities increased. Plant species composition of the soybean canopy was affected by weed population densities. Mortality of H. zea larvae due to parasitism and infection with entomopathogens was greater in closed canopy and (or) weedy soybeans than in very open and (or) weed free soybeans. Predation and parasitism of corn earworm eggs were similar across nematode and weed density treatments. Natural enemy populations increased to highest levels during July in closed canopy and (or) weedy soybeans, coinciding with availability of largest prey population reservoirs. A delay in colonization of very open and (or) weed free soybeans by beneficial arthropods until mid to late August allowed greater H. zea larval survival than in closed canopy and (or) weedy soybeans. Arthropod species richness was generally greatest in closed canopy and (or) weedy soybeans during mid to late July, with differences becoming nonsignificant in August and early September. Mean and maximum ambient temperatures were higher and relative humidities lower in open canopy than in closed canopy plots. These conditions were less favorable for development of pathogens and natural enemies.     

Changes in Vertical Distribution of Pratylenchus scribneri under Potato and Corn

The vertical distribution of Pratylenchus scribneri populations was monitored under irrigated corn and potato grown in loamy sand soil. population estimates were based on the number of nematodes recovered from 100-cm³ soil samples and the roots contained therein. Reproduction was assessed by counting the number of second-stage juveniles. An index of population maturity was computed to evaluate the age structure of populations. At no time were nematodes distributed uniformly among five soil depths from 0 to 37.5 cm deep. During the summer (June-September), changes in the total number of P. scribneri and the number of second-stage juveniles recovered were not consistent among the depths sampled. Early (April-June) and late (September-November) in the season, changes in the abundance, reproduction, and maturity of populations were similar among depths. The timing and pattern of increases in numbers of nematodes suggests that variation in the abundance of P. scribneri in the soil profile beneath potato and corn was caused primarily by reproduction rather than the movement of nematodes.     

Differences in the In Vitro and In Vivo 5-Hydroxytryptamine Extraction Performance Among Three Common Microdialysis Membranes

The present study summarizes the results of an in vitro and in vivo comparison of the apparent 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid, and 3,4-dihydroxyphenylacetic acid dialysis performance of three types of membrane frequently used in intracerebral microdialysis experiments. The dialysis fiber types examined were a regenerated cellulose Cuprophan (GF), a proprietary polycarbonate ether (CMA), and a polyacrylonitrile/sodium methallylsulfonate copolymer (HOSPAL). The experiments unexpectedly revealed that the HOSPAL membrane-equipped probes displayed clearly aberrant 5-HT diffusion dynamics compared with GF and CMA probes, demonstrable not only in vitro, but also in in vivo experiments. In vitro, the GF and CMA membrane-equipped probes exhibited maximum relative recovery for 5-HT already in the first 20-min sample, whereas the 5-HT recovery of HOSPAL probes increased in a very slow and protracted manner over a period of a little less than 2 h. The GF and CMA probes further displayed an immediate washout of 5-HT when the probes were subsequently transferred to artificial CSF only-containing medium (no 5-HT), whereas approximately 2 h was required to yield near-total extinction of dialysate 5-HT with the standard HOSPAL probes. In vivo, the rat ventral hippocampal dialysate 5-HT output responses to K+ (100 mM) infusion, to Ca2+ omission, and to systemic 8-hydroxy-2-(di-n-propylamino)tetralin injection were all markedly retarded and blunted when HOSPAL instead of GF membrane-equipped probes were used. However, the 5-hydroxyindoleacetic acid and 3,4-dihydroxyphenylacetic acid extraction in vitro and in vivo were comparable using either of the membrane types.(ABSTRACT TRUNCATED AT 250 WORDS)     

High oxygen transfer rate in a new aeration system using hollow fiber membrane

A new type of bubble aeration column called a hollow fiber membrane (HFM) aeration column was proposed, which was featured in the use of hollow fiber membranes and gave a high bubble density in the column. The value of k(L)a was increased by modifying the membrane surface for making the pore size smaller. The Sauter mean diameter of bubbles (D(vs)) was 2.0 +/- 0.1 mm in the range of the superficial gas velocity from 0.02 m s(-1) to 0.065 m s(-1), while that obtained for the bubbles near the membrane was 811 mum at the superficial gas velocity of 4.0 x 10(-4) m s(-1). The difference was ascribed to the effect of coalescence of bubbles. The value of K(L)a increased in proportion to the superficial gas velocity up to 0.02 m s(-1), and was almost constant above 0.03 m s(-1). The maximum value of k(L)a, 2.5 s(-1), was higher than those of the other aeration columns reported previously. The pneumatic power consumption per unit liquid volume (P(v)) for obtaining the same k(L)a was the smallest in the HFM aeration columns. P(v), for obtaining the same interfacial area of bubbles per liquid volume, was also lower than those for other types of aeration columns. It was suggested from the measurement of bubble diameter that the larger interfacial area generated in the HFM aeration column ascribes to the larger gas holdup than the smaller D(vs). (c) 1992 John Wiley & Sons, Inc.     

Hydrolysis of butteroil by immobilized lipase using a hollow-fiber reactor: part I. lipase adsorption studies

Adsorption of proteins from a crude preparation containing a lipase from Aspergillus niger on microporous polypropylene hollow fibers was studied at six different temperatures. Langmuir isotherms accurately describe the overall adsorption equilibria. Lipase is selectively adsorbed relative to the other proteins in the crude preparation. Hence, immobilization also provides further purification of the lipase. The predictions of the Langmuir model for the change in the specific activity of lipase upon adsorption are consistent with experimental results. The loading capacity of the hollow fibers decreases and the adsorption constant increases as temperature is increased. This effect is more significant in the case of lipolytic activity than it is for the total amount of adsorbed protein. Small, positive enthalpy changes are associated with the adsorption of lipase on these hydrophobic membranes.     

A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve

A novel potassium-selective channel which is active at membrane potentials between -100 mV and +40 mV has been identified in peripheral myelinated axons of Xenopus laevis using the patch-clamp technique. At negative potentials with 105 mM-K on both sides of the membrane, the channel at 1 kHz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. Measurements with resolution up to 10 kHz revealed a single-channel conductance of 49 pS with 105 mM-K and 17 pS with 2.5 mM-K on the outer side of the membrane. The channel was selective for K ions over Na ions (PNa/PK = 0.033). The probability of being within a burst in outside-out patches varied from patch to patch (> 0.2, but often > 0.9), and was independent of membrane potential. Open-time histograms were satisfactorily described with a single exponential (tau o = 0.09 msec), closed times with the sum of three exponentials (tau c = 0.13, 5.9, and 36.6 msec). Sensitivity to external tetraethylammonium was comparatively low (IC50 = 19.0 mM). External Cs ions reduced the apparent unitary conductance for inward currents at Em = -90 mV (IC50 = 1.1 mM). Ba and, more potently, Zn ions lowered not only the apparent single-channel conductance but also open probability. The local anesthetic bupivacaine with high potency reduced probability of being within a burst (IC50 = 165 nM). The flickering K channel is clearly different from the other five types of K channels identified so far in the same preparation. We suggest that this channel may form the molecular basis of the resting potential in vertebrate myelinated axons.     

Depolymerization of cortical microtubules is not a primary cause of chilling injury in corn (Zea mays L. cv Black Mexican Sweet) suspension culture cells

Cold-induced depolymerization of cortical microtubules were examined in suspension culture cells of corn (Zea mays L. cv Black Mexican Sweet) at various stages of chilling. In an attempt to determine whether microtubule depolymerization contributes to chilling injury, experiments were carried out with and without abscisic acid (ABA) pretreatment, since ABA reduces the severity of chilling injury in these cells. Microtubule depolymerization was detectable after 1 h at 4°C and became more extensive as the chilling was prolonged. There was little chilling injury after 1 d at 4°C in either ABA-treated or non-ABA-treated cells. After 3 d at 4°C, there was about 26% injury for ABA-treated and 40% injury for non-ABA-treated cells, as evaluated by 2,3,5-triphenyl-tetrazolium chloride reduction and by regrowth. After 1d at 4°C, less than 10% of cells retained full arrays of microtubules in both ABA-treated and non-ABA-treated cells, the remainder having either partial arrays or no microtubules. After 3d at 4°C, about 90% of cells showed complete or almost complete depolymerization of microtubules in both ABA-treated and non-ABA-treated cells. ABA did not stabilize the cortical microtubules against cold-induced depolymerization. In about 66% of ABA-treated cells and 57% of non-ABA-treated cells that had been held at 4°C for 3d, repolymerization of cortical microtubules occurred after 3h at 28°C. These results argue against the hypothesis that depolymerization of cortical microtubules is a primary cause of chilling injury.     

Influence of corn planting date on the life stage development and phenology of Diabrotica virgifera virgifera

Under field conditions in eastern South Dakota, USA three different planting dates of corn and three times of egg infestation were used to imposed synchronous and asynchronous timing of corn growth and Diabrotica virgifera virgifera LeConte egg hatch and subsequent development. Median occurrence of each of the three larval stages and of the adult stage for each of the infestation-planting treatments was determined by relating occurrence to thermal units and to days after infestation. No significant differences were found among the treatments for median occurrence of each life stage when the thermal unit approach was used. However, significant differences were found among treatments for median occurrence when the day after infestation approach was used. Consistent parameters are needed for prediction of the occurrence of life stages of this insect. Despite the various imposed conditions, this study indicates that the least variable method of predicting life stage occurrence and adult emergence of D. v. virgifera was the use of thermal unit accumulations (base 11°C).

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Résumé Dans les conditions de l'est du Sud Dakota (USA), 3 dates de semailles de maïs et 3 dates de contamination avec des ufs de D. virgifera virgifera LeConte ont servi à imposer ou à empêcher la synchronisation des éclosions des ufs et par conséquent des développements ultérieurs. Les dates médianes d'apparition de chacun des 3 stades larvaires et des imagos ont été déterminées en relation avec les unités de température et le nombre de jours depuis la contamination. Aucune différence significative entre les dates médianes d'apparition n'a été mise en évidence par utilisation des unités de température; par contre, ces différences deviennent significatives lorsque l'on utilise le nombre de jours depuis la contamination. Des paramètres fiables sont nécessaires pour prédire la présence des différentes stades de cet insecte. En dépit des différentes conditions imposées pour cette étude, la méthode la moins capricieuse pour prédire l'apparition d'un stade larvaire et l'émergence des adultes est la somme de températures avec une base de 11°C.

     

Structural Characteristics of the Short-Tail Fibers of T4 Bacteriophage

The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure.