Social and structural drivers of HIV vulnerability among a respondent-driven sample of feminine and non-feminine presenting transgender women who have sex with men in Zimbabwe

INTRODUCTION

We sought to characterize social and structural drivers of HIV vulnerability for transgender women (TGW) in Zimbabwe, where TGW are not legally recognized, and explore differences in vulnerability by feminine presentation.

METHODS

A secondary analysis was conducted with a sub-sample of participants recruited from a 2019 respondent-driven sampling survey that comprised men who have sex with men, TGW and genderqueer individuals assigned male sex at birth, from two cities in Zimbabwe. Survey questionnaires captured information related to socio-demographics, sexual and substance use behaviours, and social and structural barriers to HIV services. Secondary analyses were restricted to participants who identified as female, transfemale or transwomen (236/1538) and were unweighted. Descriptive statistics were used to calculate sample estimates and chi-square and Fisher's exact tests were used to assess differences in vulnerability by feminine presentation.

RESULTS

Among 236 TGW, almost half (45.3%) presented as feminine in the 6 months preceding the survey and 8.5% had ever used hormones to affirm their gender identities. Median age among TGW was 23 years (interquartile range: 20-26). Feminine presenting TGW in our sample had higher prevalence of arrest (15.9% vs. 3.9%), rejection by family/friends (38.3% vs. 14.0%), employment termination (11.2% vs. 3.9%), employment refusal (14.0% vs. 3.9%), denial of healthcare (16.8% vs. 2.3%), physical, sexual or verbal harassment or abuse (59.8% vs. 34.1%), alcohol dependence (32.7% vs. 12.4%), recent transactional sex with a male or TGW partner (30.8% vs. 13.3%) and recent non-injection drug use (38.3% vs. 20.2%) than non-feminine presenting TGW (all p-value <0.05).

CONCLUSIONS

Findings suggest that TGW, particularly feminine presenting TGW, experience social and structural inequities which may contribute to HIV vulnerability. Interventions aimed at addressing inequities, including trans competency training for providers and gender-affirming, psychosocial and legal support services for TGW, might mitigate risk.

Hepatitis B virus infection (HBV) and HIV-HBV coinfection among men who have sex with men, transgender women, and genderqueer individuals in Harare and Bulawayo Zimbabwe, 2019

Objectives

To measure HIV and Hepatitis B virus (HBV) prevalence and associated risk behaviors among men who have sex with men (MSM) and transgender women/genderqueer individuals (TGW/GQ) in Zimbabwe.

Methods

We conducted a biobehavioral survey using respondent-driven sampling (RDS) among adult MSM and TGW/GQ in Harare and Bulawayo, Zimbabwe in 2019. Participants completed a questionnaire and underwent testing for HIV and HBV.

Results

Overall, 1,510 (Harare: 694, Bulawayo 816) participants were enrolled and consented to testing; 3.8 % (58) tested positive for HBV, 22.5 % (339) tested positive for HIV, and 2.2 % (33) tested positive for both HIV and HBV. HBV prevalence was higher among participants with HIV compared to HIV-negative participants (9.7 % vs. 2.1 %, p < 0.0001). Overall, HBV prevalence was not statistically different between MSM and TGW/GQ (3.7 % vs 4.5 %, p = 0.49) nor between Harare and Bulawayo (3.3 % vs 4.3 %, p = 0.33).

Conclusions

Our survey demonstrates the prevalence of HBV among MSM and TGW/GQ is lower than other estimates of HBV among MSM in Africa but remains high among our survey population living with HIV highlighting the need to expand HBV testing and treatment services, especially among people with HIV in Zimbabwe.

Factors Associated with Having both Male and Female Recent Sexual Partnerships Among Men Who Have Sex with Men in Harare and Bulawayo, Zimbabwe

To better understand male and female sexual partnerships among men who have sex with men (MSM), we used data from a 2019 biobehavioral survey among MSM in Harare and Bulawayo, Zimbabwe to conduct bivariate analyses and multivariable logistic regression to determine whether sociodemographic characteristics and HIV-related factors were associated with having both male and female sexual partnerships within the last 6 months. Of included MSM (N = 1143), 31% reported both male and female partnerships in the last 6 months. Being married/cohabiting (adjusted odds ratio (aOR) = 8.58, 95% confidence interval (CI) = 4.92-14.95) or separated/divorced/widowed (aOR = 1.96, 95% CI = 1.24-3.08) vs. being single, and hazardous alcohol consumption (aOR = 1.58, 95% CI 1.19-2.09) were associated with higher odds of having both male and female recent partnerships. Being aged 35 + vs. 18-24 (aOR = 0.50, 95% CI = 0.31-0.81), condomless receptive anal intercourse at last sex with the main male partner (aOR = 0.43, 95% CI = 0.26-0.74), and positive HIV status (aOR = 0.46, 95% CI = 0.31-0.67) were associated with lower odds of recent male and female partnerships. MSM in Harare who reported harassment/abuse (aOR = 3.16, 95% CI = 1.72-5.79) had higher odds of both male and female partnerships than MSM in Bulawayo reporting harassment/abuse. The prevalence of both male and female recent partnerships (31%) was lower among MSM in this survey than in other biobehavioral surveys of MSM in sub-Saharan Africa. Findings suggest that MSM with recent male and female partnerships compared to MSM with only male recent partners have lower odds of positive HIV status and participate in behaviors that lower HIV risk; however, the direction of these relationships cannot be determined due to the cross-sectional nature of the data. The findings also suggest a possible connection between experiences of stigma of MSM behavior and not having both male and female partnerships that warrants further exploration. Accessible, stigma-free HIV testing and education programming that considers the potential overlap between the MSM and general populations via both male and female partnerships and the associated behaviors could be a key component of HIV elimination in Zimbabwe.

Stigma, Social Cohesion, and HIV Risk Among Sexual and Gender Minorities in Two Cities in Zimbabwe

Though stigma is a recognized contributor to the disproportionate HIV burden among sexual and gender minorities (SGM) in sub-Saharan Africa, data describing this association among Zimbabwean SGM are limited. We examined relationships between SGM stigma and HIV and the potential for social cohesion to moderate the association among Zimbabwean men who have sex with men, transgender women, and genderqueer individuals. Consenting participants (n = 1511) recruited through respondent-driven sampling for a biobehavioral survey in Harare and Bulawayo completed structured interviews and received HIV testing. Reported SGM stigma was common (68.9% in Harare and 65.3% in Bulawayo) and associated with HIV infection in Harare (adjusted prevalence ratio [aPR] = 1.82, 95% confidence interval [CI] = 1.27–2.62) and Bulawayo (aPR = 1.51, 95% CI = 1.15–2.00) in relative risk regression. Social cohesion did not moderate these relationships. Findings demonstrate stigma’s association with HIV vulnerability among Zimbabwean SGM, highlighting the need for stigma-mitigation to reduce HIV transmission in this population.

HIV care cascade and associated factors among men who have sex with men, transgender women, and genderqueer individuals in Zimbabwe: findings from a biobehavioural survey using respondent-driven sampling

BACKGROUND

Globally, men who have sex with men (MSM), transgender women, and genderqueer individuals are at greater risk for HIV than the general population although little data are available from these groups in Zimbabwe, a country with a national adult HIV prevalence of 12·9%. We aimed to examine progress towards the UNAIDS 90-90-90 treatment targets and factors associated with meeting the targets among a sample of MSM, transgender women, and genderqueer individuals in Zimbabwe.

METHODS

In this cross-sectional survey in 2019, we used respondent-driven sampling to identify MSM, transgender women, and genderqueer individuals aged at least 18 years to participate in a biobehavioural survey in Harare and Bulawayo, Zimbabwe. Participants were eligible to participate if they were assigned male at birth; had engaged in anal or oral sex with a man in the past 12 months; resided in Harare or Bulawayo for at least 1 month; spoke English, Shona, or Ndebele; provided written informed consent; and were in possession of a valid recruitment coupon if applicable. Enrolled participants completed a questionnaire and underwent HIV testing, and off-site viral load testing was done on all HIV-positive samples. Unweighted bivariate analyses and multivariable logistic regression models were used to evaluate the association of sociodemographic, behavioural, and other factors with HIV-positive status awareness among MSM, transgender women, and genderqueer individuals, and with viral load suppression among MSM. Analyses were done firstly using self-reported information and then by classifying those with a viral load of less than 200 copies per mL as being aware of their status and on treatment (viral load recategorisation).

FINDINGS

Among MSM, 248 (21%; 95% CI 19-24) of 1176 tested positive for HIV. Of those who tested positive, based on self-report, 119 (48%; 95% CI 42-54) reported knowing their HIV status, of whom 112 (94%; 88-98) reported using antiretroviral therapy (ART), of whom 89 (79%; 71-87) had viral load suppression. Based on viral load recategorisation, 180 (73%; 67-78) of 248 MSM testing HIV positive reported knowing their HIV status, of whom 174 (97%; 93-99) reported using ART, of whom 151 (87%; 81-91) had viral load suppression. 92 (28%; 23-33) of 335 transgender women and genderqueer individuals tested positive for HIV. Based on self-reports from these individuals 34 (37%; 27-48) of 92 participants reported knowing their HIV status, of whom 31 (91%; 76-98) reported using ART, of whom 27 (87%; 70-96%) had viral load suppression. Based on viral load recategorisation of data from transgender women and genderqueer participants, 53 (58%; 47-58) of 92 reported awareness of their HIV status, of whom 50 (94%; 84-99) reported using ART, of whom 46 (92%; 81-98) had viral load suppression. HIV-positive MSM aged 18-24 years had lower odds of being aware of their status than those aged at least 35 years (adjusted odds ratio [aOR] 0·34; 95% CI 0·13-0·92), as did HIV-positive MSM aged 25-34 years (aOR 0·26; 0·12-0·56). HIV-positive MSM aged 18-24 years also had a lower odds of having viral load suppression than those aged 35 years and older (aOR 0·35; 0·16-0·78), as did those aged 25-34 years (aOR 0·36; 0·19-0·67). No factors were significantly associated with awareness among transgender women and genderqueer individuals in multivariable models.

INTERPRETATION

Our survey showed that HIV prevalence was high and the largest difference between our results and the 90-90-90 treatment targets was in HIV status awareness, indicating the need for improvements in engaging MSM (especially young MSM), transgender women, and genderqueer individuals in HIV testing services.

FUNDING

US President's Emergency Plan for AIDS Relief through the US Centers for Disease Control and Prevention.

High Burden of Active Syphilis and Human Immunodeficiency Virus/Syphilis Coinfection Among Men Who Have Sex With Men, Transwomen, and Genderqueer Individuals in Zimbabwe

BACKGROUND

Syphilis increases human immunodeficiency virus (HIV) acquisition risk and impacts the immunologic and virologic response among people living with HIV (PLHIV). We assessed the prevalence of active or current syphilis and HIV/syphilis and their correlates among men who have sex with men (MSM), transwomen, and genderqueer (TGW/GQ) individuals in Zimbabwe.

METHODS

Among a respondent-driven sample of MSM and TGW/GQ who were tested for HIV and syphilis in Harare and Bulawayo, Zimbabwe in 2019 (n = 1511), multiple logistic regression was used to assess correlates of active syphilis. Unadjusted logistic regression was used among PLHIV (n = 340) due to small sample size. All analyses were unweighted as data did not reach convergence for HIV.

RESULTS

Prevalence of active syphilis overall and among PLHIV was 5.5% and 10.1%, respectively, in Harare, and 5.6% and 11.0%, respectively, in Bulawayo. Participants were more likely to have active syphilis if they were PLHIV (adjusted odds ratio [aOR], 2.2; 95% confidence interval [CI], 1.4-3.6), aged 25-34 years (aOR, 2.2 years; 95% CI, 1.3-3.8 years; reference, 18-24 years), or self-report sexually transmitted infection symptoms (aOR, 1.8; 95% CI, 1.1-3.0). Compared with Bulawayo TGW/GQ, MSM in Harare (aOR, 0.2; 95% CI, 0.1-0.5) and Bulawayo (aOR, 0.2; 95% CI, 0.1-0.4), and TGW/GQ in Harare (aOR, 0.2; 95% CI, 0.1-0.6) were less likely to have active syphilis. Among PLHIV, coinfection was 13.0% among TGW/GQ and 9.7% among MSM. Odds of coinfection were higher for those aged 25 to 34 years (OR, 3.7 years; 95% CI, 1.2-11.1 years) and lower among Harare MSM (OR, 0.2; 95% CI, 0.1-0.7), Bulawayo MSM (OR, 0.1; 95% CI, 0.0-0.4), and Harare TGW/GQ (OR, 0.1; 95% CI, 0.0-0.4) compared with Bulawayo TGW/GQ.

CONCLUSIONS

Findings highlight a high burden of syphilis among MSM and TGW/GQ and underscore the importance of HIV/syphilis detection and improved service delivery for these groups.

Characterizing acceptable and appropriate implementation strategies of a biobehavioral survey among men who have sex with men and others assigned male who have sex with men in Zimbabwe

Key populations including men who have sex with men (MSM), female sex workers, people who inject drugs, transgender persons, and prisoners account for nearly 50% of new HIV infections globally. To inform the HIV response and monitor trends in HIV prevalence and incidence among key populations, countries have increased efforts to implement biobehavioral surveys (BBS) with these groups as part of routine surveillance. Yet the marginalized nature of populations participating in a BBS requires contextually acceptable and appropriate strategies for effective implementation. We conducted a formative assessment to inform the first BBS conducted with MSM and others assigned male who have sex with men (OAMSM) in Zimbabwe, where same-sex sexual behaviors are illegal and highly stigmatized and describe applications of our findings. Qualitative data were collected through four focus groups with 32 MSM/OAMSM and 25 in-depth interviews (15 MSM/OAMSM, 10 service providers/gatekeepers) from December 2018 to January 2019. Rapid assessment techniques were employed including rapid identification of themes from audio recordings and review of detailed field notes and memos to identify key themes. Findings from this assessment included contextually relevant considerations including behaviors and terminology to avoid when working with MSM/OAMSM in Zimbabwe, appropriate compensation amounts for survey participation, proposed data collection sites, and differences in sexual openness, marital status, and networks among younger and older MSM/OAMSM. Participants also reported strong network ties suggesting respondent-driven sampling-a peer chain referral approach-to be an appropriate recruitment method in this context. Taken together, these findings highlighted key considerations and strategies for implementation to ensure the subsequent BBS in Zimbabwe was both acceptable and appropriate. These results and applications of these results are important for informing surveillance efforts and broader HIV-related engagement efforts among MSM/OAMSM in Zimbabwe as well as in other contextually similar countries in Southern Africa.

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.

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.

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.

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.