Alfalfa (Medicago sativa L.) pho2 mutant plants hyperaccumulate phosphate

In this article, we describe a set of novel alfalfa (Medicago sativa L.) plants that hyper-accumulate Phosphate ion (Pi) at levels 3- to 6-fold higher than wild-type. This alfalfa germplasm will have practical applications reclaiming Pi from contaminated or enriched soil or be used in conservation buffer strips to protect waterways from Pi run-off. Hyper-accumulating alfalfa plants were generated by targeted mutagenesis of PHOSPHATE2 (PHO2) using newly created CRISPR/Cas9 reagents and an improved mutant screening strategy. PHO2 encodes a ubiquitin conjugating E2 enzyme (UBC24) previously characterized in Arabidopsis thaliana, Medicago truncatula, and Oryza sativa. Mutations of PHO2 disrupt Pi homeostasis resulting in Pi hyper-accumulation. Successful CRISPR/Cas9 editing of PHO2 demonstrates that this is an efficient mutagenesis tool in alfalfa despite its complex autotetraploid genome structure. Arabidopsis and M. truncatula ortholog genes were used to identify PHO2 haplotypes in outcrossing tetraploid M. sativa with the aim of generating heritable mutations in both PHO2-like genes (PHO2-B and PHO2-C). After delivery of the reagent and regeneration from transformed leaf explants, plants with mutations in all haplotypes of PHO2-B and PHO2-C were identified. These plants were evaluated for morphology, Pi accumulation, heritable transmission of targeted mutations, segregation of mutant haplotypes and removal of T-DNA(s). The Agrobacterium-mediated transformation assay and gene editing reagents reported here were also evaluated for further optimization for future alfalfa functional genomic studies.

Seed Rot and Damping-off of Alfalfa in Minnesota Caused by Pythium and Fusarium Species

Globally, 15 Pythium species have been found to cause damping-off and seed rot of alfalfa, although surveys of species causing disease on alfalfa in the midwestern United States are lacking. Pathogens were isolated by a seedling baiting technique from soil samples of five alfalfa fields in Minnesota with high levels of damping-off. Of the 149 organisms isolated, 93 (62%) were identified as Pythium spp. and 43 (29%) were identified as Fusarium species. Pythium sylvaticum, P. irregulare, and P. ultimum var. ultimum were aggressive pathogens on germinating alfalfa seedlings. Strains of seven Pythium spp. pathogenic on soybean and corn were also pathogenic on alfalfa. The majority of the Fusarium isolates were identified as F. solani and F. oxysporum with a low number of F. redolens and F. incarnatum-equiseti. The F. oxysporum and F. incarnatum-equiseti strains were the most aggressive in causing seed and root rot. Pythium strains were sensitive to Apron XL (mefenoxam) and pyraclostrobin in vitro but efficacy varied when the fungicides were applied as a seed treatment. Seed treatments with Apron XL were more effective than treatments with Stamina against Pythium. The presence of aggressive, broad-host-range pathogens causing seed rot and damping-off suggests that new strategies are needed for managing this disease in alfalfa production systems.

Treatment of potato farm wastewater with sand filtration

This study examined sand filtration as a component of a potato farm wastewater treatment system. Two different sand filter designs, saturated flow and unsaturated flow, were evaluated at three different loading rates: 34, 68, and 136 L m(-2) d(-1). Filter design had a significant effect, with unsaturated flow sand filters having significantly (p < .05) better total suspended solids (TSS) removal (89%) than saturated flow sand filters did (79%). Loading rate also had a significant (p < .05) effect, given that the lowest loading rate had higher mass removal for TSS than the higher loading rates did. Overall, all sand filters removed TSS, 5-d biochemical oxygen demand, and total phosphorus well (62-99%). Total nitrogen removal was twice as high in unsaturated flow filters (53%) than in saturated flow filters (27%), because of the recurring cycle of aerobic and anaerobic conditions during sand saturation and drying in unsaturated flow sand filters.

Transgene silencing of sucrose synthase in alfalfa (Medicago sativa L.) stem vascular tissue suggests a role for invertase in cell wall cellulose synthesis

BACKGROUND

Alfalfa (Medicago sativa L.) is a widely adapted perennial forage crop that has high biomass production potential. Enhanced cellulose content in alfalfa stems would increase the value of the crop as a bioenergy feedstock. We examined if increased expression of sucrose synthase (SUS; EC 2.4.1.13) would increase cellulose in stem cell walls.

RESULTS

Alfalfa plants were transformed with a truncated alfalfa phosphoenolpyruvate carboxylase gene promoter (PEPC7-P4) fused to an alfalfa nodule-enhanced SUS cDNA (MsSUS1) or the β-glucuronidase (GUS) gene. Strong GUS expression was detected in xylem and phloem indicating that the PEPC7-P4 promoter was active in stem vascular tissue. In contrast to expectations, MsSUS1 transcript accumulation was reduced 75-90 % in alfalfa plants containing the PEPC7-P4::MsSUS1 transgene compared to controls. Enzyme assays indicated that SUS activity in stems of selected down-regulated transformants was reduced by greater than 95 % compared to the controls. Although SUS activity was detected in xylem and phloem of control plants by in situ enzyme assays, plants with the PEPC7-P4::MsSUS1 transgene lacked detectable SUS activity in post-elongation stem (PES) internodes and had very low SUS activity in elongating stem (ES) internodes. Loss of SUS protein in PES internodes of down-regulated lines was confirmed by immunoblots. Down-regulation of SUS expression and activity in stem tissue resulted in no obvious phenotype or significant change in cell wall sugar composition. However, alkaline/neutral (A/N) invertase activity increased in SUS down-regulated lines and high levels of acid invertase activity were observed. In situ enzyme assays of stem tissue showed localization of neutral invertase in vascular tissues of ES and PES internodes.

CONCLUSIONS

These results suggest that invertases play a primary role in providing glucose for cellulose biosynthesis or compensate for the loss of SUS1 activity in stem vascular tissue.

An RNA-Seq based gene expression atlas of the common bean

BACKGROUND

Common bean (Phaseolus vulgaris) is grown throughout the world and comprises roughly 50% of the grain legumes consumed worldwide. Despite this, genetic resources for common beans have been lacking. Next generation sequencing, has facilitated our investigation of the gene expression profiles associated with biologically important traits in common bean. An increased understanding of gene expression in common bean will improve our understanding of gene expression patterns in other legume species.

RESULTS

Combining recently developed genomic resources for Phaseolus vulgaris, including predicted gene calls, with RNA-Seq technology, we measured the gene expression patterns from 24 samples collected from seven tissues at developmentally important stages and from three nitrogen treatments. Gene expression patterns throughout the plant were analyzed to better understand changes due to nodulation, seed development, and nitrogen utilization. We have identified 11,010 genes differentially expressed with a fold change ≥ 2 and a P-value < 0.05 between different tissues at the same time point, 15,752 genes differentially expressed within a tissue due to changes in development, and 2,315 genes expressed only in a single tissue. These analyses identified 2,970 genes with expression patterns that appear to be directly dependent on the source of available nitrogen. Finally, we have assembled this data in a publicly available database, The Phaseolus vulgaris Gene Expression Atlas (Pv GEA), http://plantgrn.noble.org/PvGEA/ . Using the website, researchers can query gene expression profiles of their gene of interest, search for genes expressed in different tissues, or download the dataset in a tabular form.

CONCLUSIONS

These data provide the basis for a gene expression atlas, which will facilitate functional genomic studies in common bean. Analysis of this dataset has identified genes important in regulating seed composition and has increased our understanding of nodulation and impact of the nitrogen source on assimilation and distribution throughout the plant.

An RNA-Seq transcriptome analysis of orthophosphate-deficient white lupin reveals novel insights into phosphorus acclimation in plants

Phosphorus, in its orthophosphate form (P(i)), is one of the most limiting macronutrients in soils for plant growth and development. However, the whole-genome molecular mechanisms contributing to plant acclimation to P(i) deficiency remain largely unknown. White lupin (Lupinus albus) has evolved unique adaptations for growth in P(i)-deficient soils, including the development of cluster roots to increase root surface area. In this study, we utilized RNA-Seq technology to assess global gene expression in white lupin cluster roots, normal roots, and leaves in response to P(i) supply. We de novo assembled 277,224,180 Illumina reads from 12 complementary DNA libraries to build what is to our knowledge the first white lupin gene index (LAGI 1.0). This index contains 125,821 unique sequences with an average length of 1,155 bp. Of these sequences, 50,734 were transcriptionally active (reads per kilobase per million reads ≥ 3), representing approximately 7.8% of the white lupin genome, using the predicted genome size of Lupinus angustifolius as a reference. We identified a total of 2,128 sequences differentially expressed in response to P(i) deficiency with a 2-fold or greater change and P ≤ 0.05. Twelve sequences were consistently differentially expressed due to P(i) deficiency stress in three species, Arabidopsis (Arabidopsis thaliana), potato (Solanum tuberosum), and white lupin, making them ideal candidates to monitor the P(i) status of plants. Additionally, classic physiological experiments were coupled with RNA-Seq data to examine the role of cytokinin and gibberellic acid in P(i) deficiency-induced cluster root development. This global gene expression analysis provides new insights into the biochemical and molecular mechanisms involved in the acclimation to P(i) deficiency.

Hypothermia in very low birth weight infants: distribution, risk factors and outcomes

OBJECTIVE

The objective of this study was to study the epidemiology of neonatal hypothermia in preterm infants using World Health Organization (WHO) temperature criteria.

STUDY DESIGN

A population-based cohort of 8782 very low birth weight (VLBW) infants born in California neonatal intensive care units in 2006 and 2007. Associations between admission hypothermia and maternal and neonatal characteristics and outcomes were determined using logistic regression.

RESULT

In all, 56.2% of infants were hypothermic. Low birth weight, cesarean delivery and a low Apgar score were associated with hypothermia. Spontaneous labor, prolonged rupture of membranes and antenatal steroid administration were associated with decreased risk of hypothermia. Moderate hypothermia was associated with higher risk of intraventricular hemorrhage (IVH). Moderate and severe hypothermic conditions were associated with risk of death.

CONCLUSION

Hypothermia by WHO criteria is prevalent in VLBW infants and is associated with IVH and mortality. Use of WHO criteria could guide the need for quality improvement projects targeted toward the most vulnerable infants.

Hourglass cell development in the soybean seed coat

BACKGROUND AND AIMS

Hourglass cells (HGCs) are prominent cells in the soybean seed coat, and have potential use as 'phytofactories' to produce specific proteins of interest. Previous studies have shown that HGCs initiate differentiation at about 9 d post-anthesis (dpa), assuming their characteristic morphology by 18 dpa. This study aims to document the structural changes in HGCs during this critical period, and to relate these changes to the concurrent development of a specific soybean peroxidase (SBP) encoded by the Ep gene.

METHODS

Pods were collected from plants at specific growth stages. Fresh material was processed for analysis of Ep peroxidase activity. Tissues were processed for scanning and transmission electron microscopy, as well as extracted for western blotting. A null variety lacking expression of Ep peroxidase was grown as a control.

KEY RESULTS AND CONCLUSIONS

At 9 dpa, HGCs are typical undifferentiated plant cells, but from 12-18 dpa they undergo rapid changes in their internal and external structure. By 18 dpa, they have assumed the characteristic hourglass shape with thick cell walls, intercellular air spaces and large central vacuoles. By 45 dpa, all organelles in HGCs have been degraded. Additional observations indicate that plasmodesmata connect all cell types. SBP activity and SBP protein are detectable in the HGC before they are fully differentiated (approx. 18 dpa). In very early stages, SBP activity appears localized in a vacuole as previously predicted. These results increase our understanding of the structure and development of the HGC and will be valuable for future studies aimed at protein targeting to components of the HGC endomembrane systems.

Transcriptome analysis and molecular signature of human retinal pigment epithelium

Retinal pigment epithelium (RPE) is a polarized cell layer critical for photoreceptor function and survival. The unique physiology and relationship to the photoreceptors make the RPE a critical determinant of human vision. Therefore, we performed a global expression profiling of native and cultured human fetal and adult RPE and determined a set of highly expressed ‘signature’ genes by comparing the observed RPE gene profiles to the Novartis expression database (SymAtlas: http://wombat.gnf.org/index.html) of 78 tissues. Using stringent selection criteria of at least 10-fold higher expression in three distinct preparations, we identified 154 RPE signature genes, which were validated by qRT-PCR analysis in RPE and in an independent set of 11 tissues. Several of the highly expressed signature genes encode proteins involved in visual cycle, melanogenesis and cell adhesion and Gene ontology analysis enabled the assignment of RPE signature genes to epithelial channels and transporters (ClCN4, BEST1, SLCA20) or matrix remodeling (TIMP3, COL8A2). Fifteen RPE signature genes were associated with known ophthalmic diseases, and 25 others were mapped to regions of disease loci. An evaluation of the RPE signature genes in a recently completed AMD genomewide association (GWA) data set revealed that TIMP3, GRAMD3, PITPNA and CHRNA3 signature genes may have potential roles in AMD pathogenesis and deserve further examination. We propose that RPE signature genes are excellent candidates for retinal diseases and for physiological investigations (e.g. dopachrome tautomerase in melanogenesis). The RPE signature gene set should allow the validation of RPE-like cells derived from human embryonic or induced pluripotent stem cells for cell-based therapies of degenerative retinal diseases.

Arabidopsis UDP-sugar pyrophosphorylase: evidence for two isoforms

Arabidopsis UDP-sugar pyrophosphorylase (AtUSP, EC 2.7.7.64) is a broad substrate pyrophosphorylase that exhibits activity with GlcA-1-P, Gal-1-P and Glc-1-P. Immunoblots using polyclonal antibodies raised to recombinant AtUSP demonstrated the presence of two USP isoforms of approximately 70 kDa (USP1) and 66 kDa (USP2) in crude extracts of Arabidopsis tissues. The 66 kDa isoform was not the result of proteolytic cleavage of USP1 during extraction. Trypsin digestion of bands on SDS gels corresponding to the location of the two isoforms followed by tandem mass spectrometry confirmed that USP peptides were present in both bands. Both USP isoforms were detected in the cytosol as determined by immunoblots of cellular fractions obtained by differential centrifugation. However, some USP1 was also detected in the microsomal fraction. Immunoprecipitation assays demonstrated that AtUSP antibodies removed USP activity (UDP-GlcA-->GlcA-1-P) measured in floret extracts. These results indicate that USP is the only pyrophosphorylase that utilizes UDP-GlcA as a substrate and suggest that it serves as the terminal enzyme of the myo-inositol oxidation pathway.

Receptor tyrosine kinase inhibitors AG013764 and AG013711 reduce choroidal neovascularization in rat eye

Age-related macular degeneration (AMD) is the major cause of blindness for people over 60. In the "wet" form of AMD compounds targeting growth factor signaling pathways such as VEGF have been a major focus for therapeutic interventions. In a previously developed rat model of CNV, we utilized two receptor tyrosine kinase inhibitors (RTKi) to block VEGFR-1, VEGFR-2 and PDGFR signaling following the establishment of CNV. AAV-VEGF(165) was injected into the subretinal space of rats at postnatal days 15-17. Six weeks later, a suspension of RTK inhibitors, AG013764 or AG013711, was injected intraperitoneally (IP, twice daily) or intravitreally (every five days) over a two week period. FITC-dextran whole-mounts of RPE-choroid-sclera were prepared after the animals were sacrificed. CNV area was quantified using Neurolucida to measure the hyperfluorescence on FITC-dextran whole-mounts. Histology and immunohistochemistry were performed as described previously. VEGF expression in control and treated eyes was confirmed by immunohistochemistry and histological sections indicated recovery of retinal morphology and CNV reduction in treated eyes. In the animals IP injected with AG013764 or AG013711 the mean CNV level was reduced by 25 to 33% compared to control, but this effect did not achieve statistical significance. Intravitreal injections of AG013764 or AG013711 reduced the level of CNV by approximately 60% compared to control (p<0.005 or p<0.05, respectively). These data show that two RTK inhibitors, AG013764 or AG013711, delivered intravitreally, significantly reduce blood vessel proliferation in this AAV-VEGF(165) model of CNV.

Characterization of a novel glycine-rich protein from the cell wall of maize silk tissues

The isolation, characterization and regulation of expression of a maize silk-specific gene is described. zmgrp5 (Zea mays glycine-rich protein 5) encodes a 187 amino acid glycine-rich protein that displays developmentally regulated silk-specific expression. Northern, Western, in situ mRNA hybridization and transient gene expression analyses indicate that zmgrp5 is expressed in silk hair and in cells of the vascular bundle and pollen tube transmitting tissue elements. The protein is secreted into the extracellular matrix and is localized in the cell wall fraction mainly through interactions mediated by covalent disulphide bridges. Taken together, these results suggest that the protein may play a role in maintaining silk structure during development. This is the first documented isolation of a stigma-specific gene from maize, an important agronomic member of the Poaceae family.

Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula

Legume rhizobia symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture and in the Earth's nitrogen cycle. Signaling between rhizobia and legumes initiates development of a unique plant organ, the root nodule, where bacteria undergo endocytosis and become surrounded by a plant membrane to form a symbiosome. Between this membrane and the encased bacteria exists a matrix-filled space (the symbiosome space) that is thought to contain a mixture of plant- and bacteria-derived proteins. Maintenance of the symbiosis state requires continuous communication between the plant and bacterial partners. Here, we show in the model legume Medicago truncatula that a novel family of six calmodulin-like proteins (CaMLs), expressed specifically in root nodules, are localized within the symbiosome space. All six nodule-specific CaML genes are clustered in the M. truncatula genome, along with two other nodule-specific genes, nodulin-22 and nodulin-25. Sequence comparisons and phylogenetic analysis suggest that an unequal recombination event occurred between nodulin-25 and a nearby calmodulin, which gave rise to the first CaML, and the gene family evolved by tandem duplication and divergence. The data provide striking evidence for the recruitment of a ubiquitous Ca(2+)-binding gene for symbiotic purposes.

Preparation of soybean seed samples for FT-IR microspectroscopy

Typical preparation of seed samples for infrared (IR) microspectroscopy involves imbibition of the seed for varying time periods followed by cryosectioning. Imbibition, however, may initiate germination even at 4 degrees C with associated changes in the chemistry of the sample. We have found that it is possible to section seeds that are sufficiently hard, such as soybeans, on a standard laboratory microtome without imbibition. The use of dry sectioning of unimbibed seeds is reported here, as well as a comparison of different mounting media and modes of analysis. Glycerol, Tissue-Tek, and ethanol were used as mounting media, and the quality of the resulting spectra was assessed. Ethanol was the preferred mountant, because it dried quickly with no residue and thus did not interfere with the spectrum of interest. Analysis in transmission mode using barium fluoride windows to hold the samples was compared with transmission-reflection analysis with sections mounted on special infrared-reflecting slides. The two modes of analysis performed well in different regions of the spectrum. The mode of analysis (transmission vs. transmission-reflection) should be based on the components of greatest interest in the sample.

Experimental Bin Drenching System for Testing Biocontrol Agents to Control Postharvest Decay of Apples

A portable drencher capable of drenching a single bin of fruit was built to simulate the commercial application of chemicals to harvested apples in small orchard operations in the central and eastern United States. The drencher required as little as 125 liters of the treatment solution and permitted various bin travel speeds. Wounded apples were placed midway between the bottom and top of the bin, in the center, and near the four corners of the bin (20 fruit per location) and covered with enough unwounded apples to fill the bin. The bins were drenched with a suspension containing Penicillium expansum at 2 × 10⁴ conidia per ml in 2000, 5 × 10³ conidia per ml in 2001, and 3 × 10³ conidia per ml in 2002 and 2003. In 2000 and 2003, the additional treatments included a combination of P. expansum with the yeast Metschnikowia pulcherrima at ~;1.2 × 10⁷ CFU/ml, and in 2003 a combination with 2% sodium bicarbonate (SB) or a mixture of the yeast and SB. After 3 months of storage at ~;2°C, at all P. expansum conidial concentrations, more than 90% of wounded fruit developed decay on 'Golden Delicious', 'Delicious', and 'Rome' apples in the 2000-02 experiments. In 2003, 66 and 33.1% of the wounded fruit developed decay on 'Delicious' and 'Golden Delicious', respectively. The application of the antagonist reduced decay to 39 and 3.3% on 'Golden Delicious' in 2000 and 2003, respectively, and to 26% on 'Delicious' in 2003. The addition of SB reduced decay on both cultivars and, in combination with the yeast, was the most effective treatment on 'Golden Delicious'. This portable drencher can be very useful for evaluating different treatments applied to apples after harvest at the commercial level.

Effect of Prohexadione-Calcium Dose Level on Shoot Growth and Fire Blight in Young Apple Trees

Prohexadione-calcium suppresses both shoot growth and fire blight in apple. In young apple orchards, there are conflicting requirements to control fire blight and allow sufficient tree growth for tree establishment. Application of prohexadione-calcium to various cultivars of orchard-grown apple trees ranging in age from newly planted to fifth-leaf trees indicated that fewer high-dose (125 or 250 mg ·liter^-1) applications of prohexadione-calcium provided a better balance between fire blight control and growth in young orchards than multiple low-dose (30 or 63 mg·liter^-1) applications. The response of early-season shoot growth to prohexadione-calcium treatment dose was linear. However, trees that received high doses of prohexadione-calcium tended to grow more in the latter part of the season, resulting in little or no difference in total seasonal growth between trees that received a few high or multiple low doses of prohexadione-calcium. Enhancement of fire blight resistance by prohexadione-calcium was correlated with shoot growth suppression at the time of inoculation, and the resistance response to prohexadione-calcium treatment dose was linear. Fire blight management strategies that use prohexadione-calcium in young apple orchards are discussed.

Molecular control of acid phosphatase secretion into the rhizosphere of proteoid roots from phosphorus-stressed white lupin

White lupin (Lupinus albus) grown under P deficiency displays a suite of highly coordinated adaptive responses. Included among these is secretion of copious amounts of acid phosphatase (APase). Although numerous reports document that plants secrete APases in response to P deficiency, little is known of the biochemical and molecular events involved in this process. Here we characterize the secreted APase protein, cDNA, and gene from white lupin. The secreted APase enzyme is a glycoprotein with broad substrate specificity. It is synthesized as a preprotein with a deduced M(r) of 52,000 containing a 31-amino acid presequence. Analysis of the presequence predicts that the protein is targeted to outside the cell. The processed protein has a predicted M(r) of 49,000 but migrates as a protein with M(r) of 70,000 on sodium dodecyl sulfate gels. This is likely due to glycosylation. Enhanced expression is fairly specific to proteoid roots of P-stressed plants and involves enhanced synthesis of both enzyme protein and mRNA. Secreted APase appears to be encoded by a single gene containing seven exons interrupted by six introns. The 5'-upstream putative promoter of the white lupin-secreted APase contains a 50-base pair region having 72% identity to an Arabidopsis APase promoter that is responsive to P deficiency. The white lupin-secreted APase promoter and targeting sequence may be useful tools for genetically engineering important proteins from plant roots.

ENaC- and CFTR-dependent ion and fluid transport in mammary epithelia

Mammary epithelial 31EG4 cells (MEC) were grown as monolayers on filters to analyze the apical membrane mechanisms that help mediate ion and fluid transport across the epithelium. RT-PCR showed the presence of cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial Na(+) channel (ENaC) message, and immunomicroscopy showed apical membrane staining for both proteins. CFTR was also localized to the apical membrane of native human mammary duct epithelium. In control conditions, mean values of transepithelial potential (apical-side negative) and resistance (R(T)) are -5.9 mV and 829 Omega x cm(2), respectively. The apical membrane potential (V(A)) is -40.7 mV, and the mean ratio of apical to basolateral membrane resistance (R(A)/R(B)) is 2.8. Apical amiloride hyperpolarized V(A) by 19.7 mV and tripled R(A)/R(B). A cAMP-elevating cocktail depolarized V(A) by 17.6 mV, decreased R(A)/R(B) by 60%, increased short-circuit current by 6 microA/cm(2), decreased R(T) by 155 Omega x cm(2), and largely eliminated responses to amiloride. Whole cell patch-clamp measurements demonstrated amiloride-inhibited Na(+) currents [linear current-voltage (I-V) relation] and forskolin-stimulated Cl(-) currents (linear I-V relation). A capacitance probe method showed that in the control state, MEC monolayers either absorbed or secreted fluid (2--4 microl x cm(-2) x h(-1)). Fluid secretion was stimulated either by activating CFTR (cAMP) or blocking ENaC (amiloride). These data plus equivalent circuit analysis showed that 1) fluid absorption across MEC is mediated by Na(+) transport via apical membrane ENaC, and fluid secretion is mediated, in part, by Cl(-) transport via apical CFTR; 2) in both cases, appropriate counterions move through tight junctions to maintain electroneutrality; and 3) interactions among CFTR, ENaC, and tight junctions allow MEC to either absorb or secrete fluid and, in situ, may help control luminal [Na(+)] and [Cl(-)].

Epinephrine-induced increases in [Ca2+](in) and KCl-coupled fluid absorption in bovine RPE

PURPOSE

To define the ionic basis for the apical epinephrine-induced increase of fluid absorption (J(V)) across isolated bovine RPE-choroid.

METHODS

Epinephrine-induced changes in RPE [Ca2+](in) levels were monitored with the ratioing dye fura-2. Transepithelial potential, resistance, and unidirectional fluxes of (36)Cl, (86)Rb (K substitute), and (22)Na were simultaneously determined in paired tissues from the same eye mounted in modified Ussing flux chambers. Radioisotopes (5-7 microCi) were added to the apical bath of one tissue and the basal bath of the other, and the appearance of label in the opposite bath was measured.

RESULTS

Apical epinephrine (100 nM) transiently increased [Ca2+](in) by 153 +/- 78 nM. This increase was inhibited by the alpha(1)-adrenoreceptor antagonist prazosin (1 microM) and blocked by CPA(5 microM), an inhibitor of endoplasmic reticulum Ca2+-adenosine triphosphatases (ATPases). Apical epinephrine (100 nM) more than doubled the net Cl absorption rate, increased net K ((86)Rb) absorption by fivefold, and tripled net fluid absorption (J(V)), as predicted by isotonic coupling between ion and fluid transport. The epinephrine-induced increases in ion and fluid transport were completely inhibited by apical bumetanide (100 microM).

CONCLUSIONS

Epinephrine increased fluid absorption across bovine RPE by activating apical membrane alpha(1)-adrenergic receptors, increasing [Ca2+](in), and stimulating bumetanide-sensitive Na,K,2Cl uptake at the apical membrane and KCl efflux at the basolateral membrane.

Adrenergic receptor activated ion transport in human fetal retinal pigment epithelium

PURPOSE

To identify the apical and basolateral membrane mechanisms and intracellular signaling pathways in human fetal retinal pigment epithelium (HRPE) that mediate membrane voltage and resistance changes caused by apical membrane adrenergic receptor activation.

METHODS

Intact sheets of RPE-choroid from human fetal eyes were mounted in a modified Ussing chamber. Ringer's solution composition changes on the retina-facing and choroid-facing sides of the tissue were separately controlled. Intracellular microelectrodes recorded the membrane voltage and resistance changes after the addition of pharmacologic agents to the apical or basal baths.

RESULTS

Apical adrenergic agonists, isoproterenol and epinephrine (10(-8) M), depolarized the basolateral membrane, decreased total tissue resistance (R:(t)) and increased the ratio of apical-to-basolateral membrane resistance (R:(A)/R:(B)). Experiments using antagonists for alpha(1) and ss adrenergic receptors, prazosin and propranolol, respectively, indicated that both receptor types were present. The epinephrine responses were inhibited by apical bumetanide and basal 4,4'-diisothiocyanostilbene-2,2' disulfonic acid (DIDS). A cocktail of cyclic adenosine monophosphate (cAMP)-elevating agents produced basolateral membrane voltage and resistance changes very similar to the isoproterenol responses. The cAMP-induced electrical responses were strongly inhibited by basal 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). Ionomycin (to elevate intercellular Ca(2+), [Ca(2+)](i)) produced electrical responses similar to those caused by epinephrine. The Ca(2+) responses were unaffected by NPPB but were inhibited by 3 mM DIDS in the basal bath.

CONCLUSIONS

The results provide evidence for two apical membrane adrenergic receptors, alpha(1) and ss, activated by epinephrine and isoproterenol, respectively. The membrane voltage and resistance changes produced by these two agonists mimic those produced by elevating [Ca(2+)](i) and [cAMP](i), suggesting that these ubiquitous signaling molecules activate separate basolateral membrane Cl channels inhibited by DIDS and NPPB, respectively. These two receptors, the apical membrane NaK2Cl cotransporters and the basolateral membrane Cl channels form a complex of proteins that help mediate fluid absorption across human RPE.

The seed coat-specific expression of a subtilisin-like gene, SCS1, from soybean

A seed coat-specific gene, SCS1 (Seed Coat Subtilisin 1), from soybean, Glycine max [L.] Merill, has been identified and studied. The gene belongs to a small family of genes with sequence similarity to the subtilisins, which are serine proteases. Northern blot analysis showed that SCS1 RNA accumulates to maximal levels in seed coats at 12 days post anthesis, preceding the final stages of seed coat differentiation. The SCS1 RNA was not found in other tissues including embryos, seed pods, flowers, stems, roots or leaves. In-situ hybridization studies confirmed the temporal pattern of expression observed by Northern blot analysis and further revealed a restricted pattern of RNA accumulation in thick-walled parenchyma cells of the seed coats. These cells are important in the apoplastic translocation of nutrients en route to the embryo from the vascular tissues. The tissue-specific subtilisin-like gene may be required for regulating the differentiation of the thick-walled parenchyma cells.

Assessing capacity

Health care professionals often encounter patients who refuse a recommended treatment plan. Overriding a patient's right to autonomy has ethical, legal, and moral consequences. Incapacity is the determination by a physician that a patient lacks the ability to make informed decisions about his or her health care. The fundamentals needed for evaluating and documenting patients' capacity to make decisions regarding their personal medical care are provided.

Alendronate and estrogen effects in postmenopausal women with low bone mineral density. Alendronate/Estrogen Study Group

The bisphosphonate alendronate and conjugated equine estrogens are both widely used for the treatment of postmenopausal osteoporosis. Acting by different mechanisms, these two agents decrease bone resorption and thereby increase or preserve bone mineral density (BMD). The comparative and combined effects of these medications have not been rigorously studied. This prospective, double blind, placebo-controlled, randomized clinical trial examined the effects of oral alendronate and conjugated estrogen, in combination and separately, on BMD, biochemical markers of bone turnover, safety, and tolerability in 425 hysterectomized postmenopausal women with low bone mass. In addition, bone biopsy with histomorphometry was performed in a subset of subjects. Treatment included placebo, alendronate (10 mg daily), conjugated equine estrogen (CEE; 0.625 mg daily), or alendronate (10 mg daily) plus CEE (0.625 mg daily) for 2 yr. All of the women received a supplement of 500 mg calcium daily. At 2 yr, placebo-treated patients showed a mean 0.6% loss in lumbar spine BMD, compared with mean increases in women receiving alendronate, CEE, and alendronate plus CEE of 6.0% (P < 0.001 vs. placebo), 6.0% (P < 0.001 vs. placebo), and 8.3% (P < 0.001 vs. placebo and CEE; P = 0.022 vs. alendronate), respectively. The corresponding changes in total proximal femur bone mineral density were +4.0%, +3.4%, +4.7%, and +0.3% for the alendronate, estrogen, alendronate plus estrogen, and placebo groups, respectively. Both alendronate and CEE significantly decreased biochemical markers of bone turnover, specifically urinary N-telopeptide of type I collagen and serum bone-specific alkaline phosphatase. The alendronate plus CEE combination produced slightly greater decreases in these markers than either treatment alone, but the mean absolute values remained within the normal premenopausal range. Alendronate, alone or in combination with CEE, was well tolerated. In the subset of patients who underwent bone biopsies, histomorphometry showed normal bone histology with the expected decrease in bone turnover, which was somewhat more pronounced in the combination group. Thus, alendronate and estrogen produced favorable effects on BMD. Combined use of alendronate and estrogen produced somewhat larger increases in BMD than either agent alone and was well tolerated.

Localization of peroxidase mRNAs in soybean seeds by in situ hybridization

The soybean Ep gene encodes an anionic peroxidase enzyme that accumulates in large amounts in seed coat tissues. We have isolated a second peroxidase gene, Prx2, that is also highly expressed in developing seed coat tissues. Sequence analysis of Prx2 cDNA indicates that this transcript encodes a cationic peroxidase isozyme that is far removed from Ep in peroxidase phylogeny. To determine the expression patterns for these two peroxidases in developing seeds, the abundance and localization of the Ep and Prx2 transcripts were compared by in situ hybridization. Results show the expression of Ep begins in a small number of cells flanking the vascular bundle in the seed coat, spreads to encircle the seed, and then migrates to the hourglass cells as they develop. Expression of Prx2 occurs throughout development in all cell layers of the seed coat, and is also evident in the pericarp and embryo. Nonetheless, the Ep-encoded enzyme accounts for virtually all of the peroxidase activity detected in mature seed coats. The Prx2 enzyme is either insoluble in a catalytically inactive form, or is subject to degradation during seed maturation.

Hydrophobic protein synthesized in the pod endocarp adheres to the seed surface

Soybean (Glycine max [L.] Merr.) hydrophobic protein (HPS) is an abundant seed constituent and a potentially hazardous allergen that causes asthma in persons allergic to soybean dust. By analyzing surface extracts of soybean seeds with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and amino-terminal microsequencing, we determined that large amounts of HPS are deposited on the seed surface. The quantity of HPS present varies among soybean cultivars and is more prevalent on dull-seeded phenotypes. We have also isolated cDNA clones encoding HPS and determined that the preprotein is translated with a membrane-spanning signal sequence and a short hydrophilic domain. Southern analysis indicated that multiple copies of the HPS gene are present in the soybean genome, and that the HPS gene structure is polymorphic among cultivars that differ in seed coat luster. The pattern of HPS gene expression, determined by in situ hybridization and RNA analysis, shows that HPS is synthesized in the endocarp of the inner ovary wall and is deposited on the seed surface during development. This study demonstrates that a seed dust allergen is associated with the seed luster phenotype in soybean and that compositional properties of the seed surface may be altered by manipulating gene expression in the ovary wall.

NADH-glutamate synthase in alfalfa root nodules. Genetic regulation and cellular expression

NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) is a key enzyme in primary nitrogen assimilation in alfalfa (Medicago sativa L.) root nodules. Here we report that in alfalfa, a single gene, probably with multiple alleles, encodes for NADH-GOGAT. In situ hybridizations were performed to assess the location of NADH-GOGAT transcript in alfalfa root nodules. In wild-type cv Saranac nodules the NADH-GOGAT gene is predominantly expressed in infected cells. Nodules devoid of bacteroids (empty) induced by Sinorhizobium meliloti 7154 had no NADH-GOGAT transcript detectable by in situ hybridization, suggesting that the presence of the bacteroid may be important for NADH-GOGAT expression. The pattern of expression of NADH-GOGAT shifted during root nodule development. Until d 9 after planting, all infected cells appeared to express NADH-GOGAT. By d 19, a gradient of expression from high in the early symbiotic zone to low in the late symbiotic zone was observed. In 33-d-old nodules expression was seen in only a few cell layers in the early symbiotic zone. This pattern of expression was also observed for the nifH transcript but not for leghemoglobin. The promoter of NADH-GOGAT was evaluated in transgenic alfalfa plants carrying chimeric beta-glucuronidase promoter fusions. The results suggest that there are at least four regulatory elements. The region responsible for expression in the infected cell zone contains an 88-bp direct repeat.

cAMP-dependent absorption of chloride across airway epithelium

Elevated levels of Na and Cl in airway surface liquid may play a major role in the airway pathology of cystic fibrosis (CF) (J. J. Smith, S. M. Travis, E. P. Greenberg, and M. J. Welsh. Cell 85: 229-236, 1996) and could be caused by block of transcellular Cl absorption due to lack of a functional CF transmembrane conductance regulator (CFTR). To test for transcellular absorption of Cl across non-CF epithelium, we studied how fluid absorption was affected by the opening and closing of Cl channels. Forskolin (an activator of CFTR) tripled fluid absorption across primary cultures of bovine tracheal epithelium but had no effect on human cells. However, in both species, fluid absorption was markedly inhibited by 5-nitro-2-(3-phenylpropylamino)benzoate, a blocker of CFTR. Microelectrode studies suggested that the magnitude of the absorptive response to forskolin in bovine cells depended on the size of an inwardly directed electrochemical driving force for Cl movement across the apical membrane. Patch-clamp measurements of bovine cells revealed CFTR in the apical membrane and a cAMP-activated, inwardly rectifying Cl channel in the basolateral membrane. We conclude that a significant fraction of absorbed Cl passes transcellularly in bovine tracheal epithelial cultures, with CFTR as the path of entry in the apical membrane and a novel cAMP-activated Cl channel as the exit route in the basolateral membrane. Our data further indicate that a similar pathway may exist in non-CF human tracheal epithelium.

Pseudomonas aeruginosa induces changes in fluid transport across airway surface epithelia

Fluid transport across cultures of bovine tracheal epithelium was measured with a capacitance probe technique. Baseline fluid absorption (Jv) across bovine cells of 3.2 microliter. cm-2. h-1 was inhibited by approximately 78% after 1 h of exposure to suspensions of Pseudomonas aeruginosa, with a concomitant decrease in transepithelial potential (TEP) and increase in transepithelial resistance (Rt). Effects of P. aeruginosa were blocked by amiloride, which decreased Jv by 112% from baseline of 2.35 +/- 1.25 microliter. cm-2. h-1, increased Rt by 101% from baseline of 610 +/- 257 Omega. cm2, and decreased TEP by 91% from baseline of -55 +/- 18.5 mV. Microelectrode studies suggested that effects of P. aeruginosa on amiloride-sensitive Na absorption were due in part to a block of basolateral membrane K channels. In the presence of Cl transport inhibitors [5-nitro-2-(3-phenylpropylamino)-benzoic acid, H2-DIDS, and bumetanide], P. aeruginosa induced a fluid secretion of approximately 2.5 +/- 0.4 microliter. cm-2. h-1 and decreased Rt without changing TEP. However, these changes were abolished when the transport inhibitors were used in a medium in which Cl was replaced by an impermeant organic anion. Filtrates of P. aeruginosa suspensions had no effect on Jv, TEP, or Rt. Mutants lacking exotoxin A or rhamnolipids or with defective lipopolysaccharide still inhibited fluid absorption and altered bioelectrical properties. By contrast, mutations in the rpoN gene encoding a sigma factor of RNA polymerase abolished actions of P. aeruginosa. In vivo, changes in transepithelial salt and water transport induced by P. aeruginosa may alter viscosity and ionic composition of airway secretions so as to foster further bacterial colonization.

Alfalfa malate dehydrogenase (MDH): molecular cloning and characterization of five different forms reveals a unique nodule-enhanced MDH

Malate dehydrogenase (MDH) catalyzes the readily reversible reaction of oxaloacetate reversible malate using either NADH or NADPH as a reductant. In plants, the enzyme is important in providing malate for C4 metabolism, pH balance, stomatal and pulvinal movement, respiration, beta-oxidation of fatty acids, and legume root nodule functioning. Due to its diverse roles the enzyme occurs as numerous isozymes in various organelles. While antibodies have been produced and cDNAs characterized for plant mitochondrial, glyoxysomal, and chloroplast forms of MDH, little is known of other forms. Here we report the cloning and characterization of cDNAs encoding five different forms of alfalfa MDH, including a plant cytosolic MDH (cMDH) and a unique novel nodule-enhanced MDH (neMDH). Phylogenetic analyses show that neMDH is related to mitochondrial and glyoxysomal MDHs, but diverge from these forms early in land plant evolution. Four of the five forms could effectively complement an E. coli Mdh- mutant. RNA and protein blots show that neMDH is most highly expressed in effective root nodules. Immunoprecipitation experiments show that antibodies produced to cMDH and neMDH are immunologically distinct and that the neMDH form comprises the major form of total MDH activity and protein in root nodules. Kinetic analysis showed that neMDH has a turnover rate and specificity constant that can account for the extraordinarily high synthesis of malate in nodules.

Multicenter study of oxygen-insensitive handheld glucose point-of-care testing in critical care/hospital/ambulatory patients in the United States and Canada

OBJECTIVES

Existing handheld glucose meters are glucose oxidase (GO)-based. Oxygen side reactions can introduce oxygen dependency, increase potential error, and limit clinical use. Our primary objectives were to: a) introduce a new glucose dehydrogenase (GD)-based electrochemical biosensor for point-of-care testing; b) determine the oxygen-sensitivity of GO- and GD-based electrochemical biosensor test strips; and c) evaluate the clinical performance of the new GD-based glucose meter system in critical care/hospital/ambulatory patients.

DESIGN

Multicenter study sites compared glucose levels determined with GD-based biosensors to glucose levels determined in whole blood with a perchloric acid deproteinization hexokinase reference method. One site also studied GO-based biosensors and venous plasma glucose measured with a chemistry analyzer. Biosensor test strips were used with a handheld glucose monitoring system. Bench and clinical oxygen sensitivity, hematocrit effect, and precision were evaluated.

SETTING

The study was performed at eight U.S. medical centers and one Canadian medical center.

PATIENTS

There were 1,248 patients.

RESULTS

The GO-based biosensor was oxygen-sensitive. The new GD-based biosensor was oxygen-insensitive. GD-based biosensor performance was acceptable: 2,104 (96.1%) of 2,189 glucose meter measurements were within +/-15 mg/dL (+/-0.83 mmol/L) for glucose levels of < or = 100 mg/dL (< or = 5.55 mmol/L) or within +/-15% for glucose levels of > 100 mg/dL, compared with the whole-blood reference method results. With the GD-based biosensor, the percentages of glucose measurements that were not within the error tolerance were comparable for different specimen types and clinical groups. Bracket predictive values were acceptable for glucose levels used in therapeutic management.

CONCLUSIONS

The performance of GD-based, oxygen-insensitive, handheld glucose testing was technically suitable for arterial specimens in critical care patients, cord blood and heelstick specimens in neonates, and capillary and venous specimens in other patients. Multicenter findings benchmark the performance of bedside glucose testing devices. With the new +/-15 mg/dL --> 100 mg/dL --> +/-15% accuracy criterion, point-of-care systems for handheld glucose testing should score 95% (or better), as compared with the recommended reference method. Physiologic changes, preanalytical factors, confounding variables, and treatment goals must be taken into consideration when interpreting glucose results, especially in critically ill patients, for whom arterial blood glucose measurements will reflect systemic glucose levels.

Ultraspatially-resolved synchrotron infrared microspectroscopy of plant tissue in situ

Routine use of 6 microm or 12 microm apertures with synchrotron microspectroscopy provide good spectra without excessive co-addition of scans. 100% mapping by stepping in pixel sized increments reveals chemical heterogeneity within cellular dimensions. The brightness of the synchrotron source and the absence of thermal noise compared to a conventional thermal (globar) source yields favorable signal-to-noise operation. The nondivergent characteristics of the source result in minimal loss of radiation at the aperture, hence, spatial resolution approaches the diffraction limit. Details of cellular dimensions are then localized within any maps produced and individual spectra obtained from adjacent pixels clearly shows the striking difference in chemistry even within a microscopic vicinity. In this report the mapping of plant tissue with the synchrotron is contrasted to previous lower spatial resolution mapping experiments done with the globar on similar materials using interpolation between separated sampling spots and larger apertures.

Resident learning and knowledge retention from resident-prepared chest radiology conferences

RATIONALE AND OBJECTIVES

The authors assessed resident learning and retention of knowledge from resident-prepared chest radiology conferences.

MATERIALS AND METHODS

Radiology residents presented five chest conferences to their peers during a 5-month interval; the conferences were modeled on a case presentation format. Tests were given 5 minutes before each conference (pretest) and immediately after each conference (posttest). The tests were readministered as a final examination 6 months later, at which time the residents were asked to evaluate the conference format.

RESULTS

Conference attendance ranged from six to 11 residents. Mean posttest scores were statistically significantly higher than mean pretest scores (P < .0001). Six-month retention scores were higher than pretest scores (P < .05) but lower than posttest scores (P < .05). On a scale of 1-6, with 1 representing strongly disagree and 6 strongly agree, residents strongly agreed that the conferences provided an excellent learning experience (mean score, 5.27).

CONCLUSION

Resident-prepared conferences are effective for teaching residents chest radiology. Resident testing at 6 months demonstrated retention of knowledge above pretest levels but lower than posttest levels.

Nitrogen assimilation in alfalfa: isolation and characterization of an asparagine synthetase gene showing enhanced expression in root nodules and dark-adapted leaves

Asparagine, the primary assimilation product from N2 fixation in temperate legumes and the predominant nitrogen transport product in many plant species, is synthesized via asparagine synthetase (AS; EC 6.3.5.4). Here, we report the isolation and characterization of a cDNA and a gene encoding the nodule-enhanced form of AS from alfalfa. The AS gene is comprised of 13 exons separated by 12 introns. The 5' flanking region of the AS gene confers nodule-enhanced reporter gene activity in transformed alfalfa. This region also confers enhanced reporter gene activity in dark-treated leaves. These results indicate that the 5' upstream region of the AS gene contains elements that affect expression in root nodules and leaves. Both AS mRNA and enzyme activity increased approximately 10- to 20-fold during the development of effective nodules. Ineffective nodules have strikingly reduced amounts of AS transcript. Alfalfa leaves have quite low levels of AS mRNA and protein; however, exposure to darkness resulted in a considerable increase in both. In situ hybridization with effective nodules and beta-glucuronidase staining of nodules from transgenic plants showed that AS is expressed in both infected and uninfected cells of the nodule symbiotic zone and in the nodule parenchyma. RNA gel blot analysis and in situ hybridization results are consistent with the hypothesis that initial AS expression in nodules is independent of nitrogenase activity.

Apical and basolateral membrane mechanisms that regulate pHi in bovine retinal pigment epithelium

pH regulation was studied in fresh explant bovine retinal pigment epithelium-choroid using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and intracellular microelectrodes. Acid recovery was HCO3 dependent, inhibited by apical amiloride and apical or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and required apical and basal Na. Alkali recovery was HCO3 dependent and inhibitable by apical or basal DIDS. Three apical and two basolateral transporters were identified. Four contribute to acid extrusion, i.e., apical Na/H exchange, apical H-lactate cotransport, and apical Na-HCO3 cotransport and basolateral Na-HCO3 cotransport. At least two contribute to alkali extrusion, i.e., apical Na-HCO3 cotransport and a basolateral HCO3-dependent, DIDS-inhibitable mechanism, possibly Na-HCO3 cotransport, Cl/HCO3 exchange, or both. The apical Na-HCO3 cotransporter is electrogenic, carrying net negative charge inward. Basal Cl removal or addition of basal HCO3 caused HCO3- and Cl-dependent alkalinizations, respectively. Apical DIDS increased both responses. These cytosolic pH (pHi) regulatory mechanisms are so tightly coupled that changes in pHi can only occur after two or more of them are inhibited. In addition, these mechanisms help provide pathways for transport of Na and HCO3 across the retinal pigment epithelium between the blood and the distal retina.

Fluid transport across cultures of human tracheal glands is altered in cystic fibrosis

1. There is evidence that defective submucosal gland secretion contributes to the airway pathology of cystic fibrosis (CF). Using a capacitance probe technique, we have compared fluid transport across submucosal gland cultures from individuals with and without CF. 2. Under baseline conditions, approximately 60% of non-CF cultures secreted fluid; the rest absorbed. In secreting tissues, amiloride increased secretion, whereas in absorbing tissues it reduced or reversed absorption. 5-Nitro-2(3-phenylpropylamino)-benzoate (NPPB) a blocker of the CF transmembrane conductance regulator (CFTR), converted secretion to absorption. Thus, the direction and magnitude of baseline fluid movement depended on a balance between active absorption of Na+ and cAMP-dependent secretion of Cl-. 3. 8-(4-Chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPT-cAMP), methacholine and luminal uridine 5'-triphosphate (UTP) all induced or increased fluid secretion across non-CF cultures. Results with NPPB and with 4,4'-diisothiocyanatostilbene-2,2'-disulphonate (DIDS), a blocker of Ca(2+)-activated Cl- channels, suggested that fluid secretion induced by CPT-cAMP was mediated primarily by CFTR; UTP acted entirely via Ca(2+)-activated Cl- channels, and methacholine activated both pathways. 4. All CF cultures showed baseline fluid absorption, which was abolished by amiloride. 5. CF cultures showed a normal secretory response to UTP, a reduced response to methacholine, and no response to CPT-cAMP. 6. Thus, the absorptive processes of airway glands are retained in CF, but the cAMP-dependent secretory process is lost. This would markedly reduce the water content of gland secretions. The resulting change in viscosity would contribute to the accumulation of airway mucus which is characteristic of this disease.

Extracellular ATP activates calcium signaling, ion, and fluid transport in retinal pigment epithelium

The presence of receptors for ATP has not been established in any native preparation of retinal neurons or glia. In the present study, we used conventional electrophysiological and [Ca2+]in fluorescence imaging techniques to investigate the effects of ATP added to Ringer's solution perfusing the retinal-facing (apical) membrane of freshly isolated monolayers of bovine retinal pigment epithelium (RPE). ATP (or UTP) produced large, biphasic voltage and resistance changes with a Kd of approximately 5 microM for ATP and approximately 1 microM for UTP. Electrical and pharmacological evidence indicates that the first and second phases of the response are attributable to an increase in basolateral membrane Cl conductance and a decrease in apical membrane K conductance, respectively. The ATP-induced responses were not affected by adenosine, but were reduced by the P2-purinoceptor blocker suramin. ATP also produced a large, transient increase in [Ca2+]in that was blocked by cyclopiazonic acid, an inhibitor of endoplasmic reticulum Ca2+-ATPases. The calcium buffer BAPTA attenuated the voltage effects of ATP. We also found that apical DIDS significantly inhibited the ATP-evoked [Ca2+]in and electrical responses, suggesting that DIDS blocked the purinoceptor. Measurements of fluid movement across the RPE using the capacitance probe technique demonstrated a significant increase in fluid absorption by apical UTP. These data indicate the presence of metabotropic P2Y/P2U-purinoceptors at the RPE apical membrane and implicate extracellular ATP in vivo as a retinal signaling molecule that could help regulate the hydration and chemical composition of the subretinal space.

Cyclic responding by pigeons on the peak timing procedure

The present experiment examined whether discrimination learning shapes the single-peaked response distributions usually obtained with the peak procedure. Two sources of learning in pigeons were disclosed: learning to respond near the time of reinforcement on fixed interval (FI) trials and learning to withhold responding once the FI duration had elapsed on peak interval (PI) trials. Pigeons also produced a highly unexpected second peak in responding on nonreinforced PI trials at 3 times the FI duration. Follow-up experiments showed that a 1:4 FI:PI duration ratio supported double peaks, but only 1 peak was obtained with a 1:8 FI:PI duration ratio. Finally, 4 peaks could be observed on extra-long PI trials under a 1:4:8 FI:PI:PI ratio procedure. The multiple-peaked response distributions are an unprecedented finding that present a major challenge to any theory of time perception.

Cyclic responding by pigeons on the peak timing procedure

The present experiment examined whether discrimination learning shapes the single-peaked response distributions usually obtained with the peak procedure. Two sources of learning in pigeons were disclosed: learning to respond near the time of reinforcement on fixed interval (FI) trials and learning to withhold responding once the FI duration had elapsed on peak interval (PI) trials. Pigeons also produced a highly unexpected second peak in responding on nonreinforced PI trials at 3 times the FI duration. Follow-up experiments showed that a 1:4 FI:PI duration ratio supported double peaks, but only 1 peak was obtained with a 1:8 FI:PI duration ratio. Finally, 4 peaks could be observed on extra-long PI trials under a 1:4:8 FI:PI:PI ratio procedure. The multiple-peaked response distributions are an unprecedented finding that present a major challenge to any theory of time perception.

A new reusable instrument designed for simple and secure knot tying in laparoscopic surgery

This new instrument is a metal cannula designed for use in creating controlled intracorporeal knots similar to instrument ties used in open surgery. It can therefore be used in a number of situations in laparoscopic surgery for ligation in continuity-for example, of the undivided cystic duct or of a vascular pedicle or for ligation of the cut end of a pedicle held in artery forceps. The cannula is designed to be loaded with 0 suture material and has a tip that readily penetrates the abdominal wall through a 3-mm skin incision, so it can be introduced either directly or through an introducer sleeve in a laparoscopic port. A curved dissecting forceps is used for knot formation. The knot is tightened by pushing the cannula with the other hand, and further throws are applied. The tip is profiled so that the knot, which is formed is pushed down into position without slippage or damage to the suture material.

Nonsteroidal anti-inflammatory drugs alter chloride and fluid transport in bovine retinal pigment epithelium

Nonsteroidal anti-inflammatory drugs (NSAIDs) were added to the solutions bathing the apical membrane of bovine retinal pigment epithelium (RPE)-choroid explants. For example, niflumic acid (100 microM) depolarized the basolateral membrane voltage (VB) by approximately 12 mV, increased transepithelial potential by 4.5 mV, decreased intracellular Cl activity by 13 mM, decreased transepithelial resistance by 17 omega.cm2, and increased the ratio of apical to basolateral membrane resistance nearly threefold. All of these changes are consistent with an increase in basolateral membrane Cl conductance. In addition, niflumic acid caused intracellular Ca concentration to decrease by 16 nM and fluid transport rate to increase by 1.5 microliters.cm-2.h-1. Flufenamic acid, which is structurally very similar to niflumic acid, had the opposite effects on membrane voltage and resistance. Basal application of the Cl channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or current clamping VB to the reversal potential for Cl practically abolished the niflumic acid response. The niflumic acid results suggest that certain NSAIDs can directly alter Cl conductance in the bovine RPE, apparently independently of cyclooxygenase inhibition.

The anterior abdominal wall in laparoscopic procedures and limitations of laparoscopic simulators

BACKGROUND

Maneuvers involving two-handed techniques such as intracorporeal suturing and knot-tying during laparoscopy are intrinsically more difficult than ones performed during open surgery.

METHODS

The use of simulators to practice and teach specialized techniques is established. However, simulators vary greatly, and few, as yet, represent the abdominal wall well.

RESULTS

This study has shown that the working angle between instruments during laparoscopic cholecystectomy is 78 degrees, and this can be increased to 117 degrees by moving the instruments laterally. In contrast, the working angle in four trainers assessed was never greater than 77 degrees.

CONCLUSIONS

This suggests that some maneuvers may be more difficult in trainers than at surgery. This has implications for training and the further development of more realistic simulators.

Identification and functional characterization of a dual GABA/taurine transporter in the bullfrog retinal pigment epithelium

Intracellular microelectrodes, fluorescence imaging, and radiotracer flux techniques were used to investigate the physiological response of the retinal pigment epithelium (RPE) to the major retinal inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). GABA is released tonically in the dark by amphibian horizontal cells, but is not taken up by the nearby Müller cells. Addition of GABA to the apical bath produced voltage responses in the bullfrog RPE that were not blocked nor mimicked by any of the major GABA-receptor antagonists or agonists. Nipecotic acid, a substrate for GABA transport, inhibited the voltage effects of GABA. GABA and nipecotic acid also inhibited the voltage effects of taurine, suggesting that the previously characterized beta-alanine sensitive taurine carrier also takes up GABA. The voltage responses of GABA, taurine, nipecotic acid, and beta-alanine all showed first-order saturable kinetics with the following Km's: GABA (Km = 160 microM), beta-alanine (Km = 250 microM), nipecotic acid (Km = 420 microM), and taurine (Km = 850 microM). This low affinity GABA transporter is dependent on external Na, partially dependent on external Cl, and is stimulated in low [K]o, which approximates subretinal space [K]o during light onset. Apical GABA also produced a significant conductance increase at the basolateral membrane. These GABA-induced conductance changes were blocked by basal Ba2+, suggesting that GABA decreased basolateral membrane K conductance. In addition, the apical membrane Na/K ATPase was stimulated in the presence of GABA. A model for the interaction between the GABA transporter, the Na/K ATPase, and the basolateral membrane K conductance accounts for the electrical effects of GABA. Net apical-to-basal flux of [3H]-GABA was also observed in radioactive flux experiments. The present study shows that a high capacity GABA uptake mechanism with unique pharmacological properties is located at the RPE apical membrane and could play an important role in the removal of GABA from the subretinal space (SRS). This transporter could also coordinate the activities of GABA and taurine in the SRS after transitions between light and dark.

Alfalfa NADH-dependent glutamate synthase: structure of the gene and importance in symbiotic N2 fixation

Glutamate synthase (GOGAT), a key enzyme in ammonia (NH+4) assimilation, occurs as two forms in plants: a ferredoxin-dependent form (Fd-GOGAT) and an NADH-dependent form (NADH-GOGAT). These enzymes are encoded by distinct genes as evidenced by their cDNA and deduced amino acid sequences. This paper reports the isolation and characterization of a NADH-GOGAT gene from alfalfa (Medicago sativa L.), the first GOGAT gene to be isolated from a eukaryote. RNase protection and primer extension experiments map the transcription start site of NADH-GOGAT to nearly identical positions. The transcribed region of this gene, 12,214 bp, is comprised of 22 exons separated by 21 introns. The 2.7 kbp region 5' from the translation initiation site confers nodule-specific reporter gene activity when used in a chimeric beta-glucuronidase (GUS) construct and transformed into Lotus corniculatus and Medicago sativa. Both infected and uninfected cells display GUS activity. The abundance of NADH-GOGAT transcripts increases substantially in developing nodules of plants infected with effective rhizobia. However, this increase is not observed when nodules are induced by a variety of ineffective rhizobial strains. Thus, unlike many other plant genes involved in root nodule NH+4 assimilation, high levels of NADH-GOGAT expression are strictly associated with effective nodules indicating that NADH-GOGAT plays a central role in the functioning of effective root nodules. An alfalfa Fd-GOGAT PCR product showing greater than 85% identity to maize Fd-GOGAT was isolated and used to investigate the contribution of this enzyme to NH+4 assimilation in nodules. Fd-GOGAT mRNA was abundant in leaves and cotyledons but was not detected in alfalfa root nodules. Fd-GOGAT in alfalfa does not appear to play a significant role in symbiotic N2 fixation.

Intravenous cholangiography and operative cholangiography: implications for laparoscopic cholecystectomy

There has been a resurgence of interest in the potential role of intravenous cholangiography with the advent of laparoscopic cholecystectomy. A retrospective review of a historical group of 185 patients undergoing cholecystectomy in whom the results of both intravenous cholangiography (IVC) and routine operative cholangiography (OC) were available was carried out. The common bile duct (CBD) was explored in 31 (16.7%) patients and choledocholithiasis confirmed in 25 (81%). IVC had shown calculi in 17 of these 25 patients (sensitivity, 68%) whereas OC demonstrated calculi in 24 (sensitivity 96%). Out of the six negative duct explorations, IVC suggested stones in two patients (specificity 66%) and OC in four patients (specificity 33%). Ultrasound scan had a sensitivity of only 48% for bile duct calculi. The accuracy of IVC was 68% and OC 84%. Intravenous cholangiography has no routine role in the preoperative assessment in patients undergoing elective cholecystectomy. In high-risk patients, alternative imaging techniques should be used.

The delayed basolateral membrane hyperpolarization of the bovine retinal pigment epithelium: mechanism of generation

1. Conventional and ion-selective double-barrelled microelectrodes were used in an in vitro preparation of bovine retinal pigment epithelium (RPE)-choroid to measure the changes in membrane voltage, resistance and intracellular Cl- activity (aCli) produced by small, physiological changes in extracellular potassium concentration ([K+]o). These apical [K+]o changes approximate those produced in the extracellular (subretinal) space between the photoreceptors and the RPE following transitions between light and dark. 2. Changing apical [K+]o from 5 to 2 mM in vitro elicited membrane voltage responses with three distinct phases. The first phase was generated by an apical membrane hyperpolarization, followed by a (delayed) basolateral membrane hyperpolarization (DBMH); the third phase was an apical membrane depolarization. The present experiments focus on the membrane and cellular mechanisms that generate phase 2 of the response, the DBMH. 3. The DBMH was abolished in the presence of apical bumetanide (100 microM); this response was completely restored after bumetanide removal. 4. Reducing apical [K+]o, adding apical bumetanide (500 mM), or removing apical Cl- decreased aCli by 25 +/- 6 (n = 8), 28 +/- 1 (n = 2) and 26 +/- 5 mM (n = 3), respectively; adding 100 microM apical bumetanide decreased aCli by 12 +/- 2 mM (n = 3). Adding apical bumetanide or removing apical bath Cl- hyperpolarized the basolateral membrane and decreased the apparent basolateral membrane conductance (GB). 5. DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid) blocked the RPE basolateral membrane Cl- conductance and inhibited the DBMH and the basolateral membrane hyperpolarization produced by apical bumetanide addition or by removal of apical Cl-o. The present results show that the DBMH is caused by delta[K]o-induced inhibition of the apical membrane Na(+)-K(+)-2Cl- cotransporter; the subsequent decrease in aCli generated a hyperpolarization at the basolateral membrane Cl- channel.

Lactate transport mechanisms at apical and basolateral membranes of bovine retinal pigment epithelium

The isolated bovine retinal pigment epithelium actively transports lactate from the apical to the basal bath. Net short-circuit [14C]lactate flux in 20 mM lactate was 0.46 +/- 0.09 mu eq.cm-2.h-1 (n = 8). In open circuit, with a physiological lactate gradient, net [14C]lactate flux was 0.66-1.31 mu eq.cm-2.h-1 (n = 3). Lactate in the apical bath caused intracellular acidifications that were saturable, apparently stereospecific, and reduced in magnitude by several H-lactate cotransport inhibitors. In the basal bath, lactate caused intracellular alkalinizations that were dependent on the presence of Na. In short circuit, 20 mM lactate in both baths reversed the direction of net transepithelial 22Na transport from secretion to absorption, suggesting the presence of basolateral Na-lactate cotransport moving lactate out of the cells. Outwardly directed Na-lactate cotransport requires a lactate:Na stoichiometry > 1.4:1, consistent with the coupled movement of Na, lactate, and net negative charge across the basolateral membrane. Intracellular microelectrode recordings showed that basal lactate hyperpolarized and apical lactate depolarized the basolateral membrane. For lactate absorption, this is a novel arrangement of membrane proteins:luminal H-lactate cotransport and serosal electrogenic Na:(n)lactate cotransport. Lactate transport across the retinal pigment epithelium may play an important role in regulating retinal metabolism and subretinal space volume and composition.

Proton-lactate cotransport in the apical membrane of frog retinal pigment epithelium

We studied lactate- and pyruvate-dependent proton transport across the apical membrane of frog RPE. The epithelium was mounted in a modified Ussing-chamber that allowed measurement of transepithelial potential and resistance while intracellular pH was measured with either intracellular microelectrodes or a pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). To estimate the rate of lactate influx from the change in intracellular pH, we used the NH4 pulse technique to measure intracellular buffering capacity and its dependence on intracellular pH. We found that the buffering capacity was 16 mM at pH1 = 7.28, and that it increased as intracellular pH decreased. Intracellular pH was monitored with the tissue bathed in nominally HCO3-free (Hepes buffered) Ringer. The perfusate on the apical side of the epithelium was then changed to a Ringer that contained between 5 and 100 mM lactate or pyruvate. When 10-100 mM lactate or pyruvate was added to the apical bath the cells acidified by 0.05-0.50 pH units. For each of these acidifications, the initial acid influx into the RPE cells was calculated from the intracellular buffering capacity and the initial rate of intracellular acidification. These influxes were plotted as functions of the concentrations of lactate or pyruvate and this relationship was analysed using Michaelis-Menten kinetics. The Km values were: 33 +/- 5 mM for lactate and 9 +/- 3 mM for pyruvate. There were no differences in the rates of acid influx caused by L- or D-lactate. The rates of acidification caused by 50 mM apical L-lactate were reversibly reduced by 56% after apical administration of probenecid (2 mM), and irreversibly reduced by 63% after apical administration of the SH-reagent mersalyl acid (2 mM). These results indicate the presence of a proton-lactate cotransport system in the apical membrane of the frog RPE.