Assessment of cryogenic pretreatment for simulating environmental weathering in the formation of surrogate micro- and nanoplastics from agricultural mulch film

Microplastics (MPs) and nanoplastics (NPs) from mulch films and other plastic materials employed in vegetable and small fruit production pose a major threat to agricultural ecosystems. For conducting controlled studies on MPs' and NPs' (MNPs') ecotoxicity to soil organisms and plants and fate and transport in soil, surrogate MNPs are required that mimic MNPs that form in agricultural fields. We have developed a procedure to prepare MPs from plastic films or pellets using mechanical milling and sieving, and conversion of the resultant MPs into NPs through wet grinding, both steps of which mimic the degradation and fragmentation of plastics in nature. The major goal of this study was to determine if cryogenic exposure of two biodegradable mulch films effectively mimics the embrittlement caused by environmental weathering in terms of the dimensional, thermal, chemical, and biodegradability properties of the formed MNPs. We found differences in size, surface charge, thermal and chemical properties, and biodegradability in soil between MNPs prepared from cryogenically treated vs. environmentally weathered films, related to the photochemical reactions occurring in the environment that were not mimicked by cryogenic treatment, such as depolymerization and cross-link formation. We also investigated the size reduction process for NPs and found that the size distribution was bimodal, with populations centered at 50 nm and 150-300 nm, and as the size reduction process progressed, the former subpopulation's proportion increased. The biodegradability of MPs in soil was greater than for NPs, a counter-intuitive trend since greater surface area exposure for NPs would increase biodegradability. The result isassociated with differences in surface and chemical properties and to minor components that are readily leached out during the formation of NPs. In summary, the use of weathered plastics as feedstock would likely produce MNPs that are more realistic than cryogenically-treated unweathered films for use in experimental studies.

A Bispecific METxMET Antibody-Drug Conjugate with Cleavable Linker Is Processed in Recycling and Late Endosomes

Most antibody-drug conjugates (ADC) approved for the treatment of cancer contain protease-cleavable linkers. ADCs that traffic to lysosomes traverse highly acidic late endosomes, while ADCs that recycle to the plasma membrane traffic through mildly acidic sorting and recycling endosomes. Although endosomes have been proposed to process cleavable ADCs, the precise identity of the relevant compartments and their relative contributions to ADC processing remain undefined. Here we show that a METxMET biparatopic antibody internalizes into sorting endosomes, rapidly traffics to recycling endosomes, and slowly reaches late endosomes. In agreement with the current model of ADC trafficking, late endosomes are the primary processing site of MET, EGFR, and prolactin receptor ADCs. Interestingly, recycling endosomes contribute up to 35% processing of the MET and EGFR ADCs in different cancer cells, mediated by cathepsin-L, which localizes to this compartment. Taken together, our findings provide insight into the relationship between transendosomal trafficking and ADC processing and suggest that receptors that traffic through recycling endosomes might be suitable targets for cleavable ADCs.

A Biparatopic Antibody-Drug Conjugate to Treat MET-Expressing Cancers, Including Those that Are Unresponsive to MET Pathway Blockade

Lung cancers harboring mesenchymal-to-epithelial transition factor (MET) genetic alterations, such as exon 14 skipping mutations or high-level gene amplification, respond well to MET-selective tyrosine kinase inhibitors (TKI). However, these agents benefit a relatively small group of patients (4%-5% of lung cancers), and acquired resistance limits response durability. An antibody-drug conjugate (ADC) targeting MET might enable effective treatment of MET-overexpressing tumors (approximately 25% of lung cancers) that do not respond to MET targeted therapies. Using a protease-cleavable linker, we conjugated a biparatopic METxMET antibody to a maytansinoid payload to generate a MET ADC (METxMET-M114). METxMET-M114 promotes substantial and durable tumor regression in xenografts with moderate to high MET expression, including models that exhibit innate or acquired resistance to MET blockers. Positron emission tomography (PET) studies show that tumor uptake of radiolabeled METxMET antibody correlates with MET expression levels and METxMET-M114 efficacy. In a cynomolgus monkey toxicology study, METxMET-M114 was well tolerated at a dose that provides circulating drug concentrations that are sufficient for maximal antitumor activity in mouse models. Our findings suggest that METxMET-M114, which takes advantage of the unique trafficking properties of our METxMET antibody, is a promising candidate for the treatment of MET-overexpressing tumors, with the potential to address some of the limitations faced by the MET function blockers currently in clinical use.

Autophagy protects tumors from T cell–mediated cytotoxicity via inhibition of TNFα-induced apoptosis

Although T cell checkpoint inhibitors have transformed the treatment of cancer, the molecular determinants of tumor cell sensitivity to T cell–mediated killing need further elucidation. Here, we describe a mouse genome–scale CRISPR knockout screen that identifies tumor cell TNFα signaling as an important component of T cell–induced apoptosis, with NF-κB signaling and autophagy as major protective mechanisms. Knockout of individual autophagy genes sensitized tumor cells to killing by T cells that were activated via specific TCR or by a CD3 bispecific antibody. Conversely, inhibition of mTOR signaling, which results in increased autophagic activity, protected tumor cells from T cell killing. Autophagy functions at a relatively early step in the TNFα signaling pathway, limiting FADD-dependent caspase-8 activation. Genetic inactivation of tumor cell autophagy enhanced the efficacy of immune checkpoint blockade in mouse tumor models. Thus, targeting the protective autophagy pathway might sensitize tumors to T cell–engaging immunotherapies in the clinic.

Mechanical formation of micro- and nano-plastic materials for environmental studies in agricultural ecosystems

Release of microplastics (MPs) and nanoplastics (NPs) into agricultural fields is of great concern due to their reported ecotoxicity to organisms that provide beneficial service to the soil such as earthworms, and the potential ability of MPs and NPs to enter the food chain. Most fundamental studies of the fate and transport of plastic particulates in terrestrial environments employ idealized MP materials as models, such as monodisperse polystyrene spheres. In contrast, plastics that reside in agricultural soils consist of polydisperse fragments resulting from degraded films employed in agriculture. There exists a need for more representative materials in fundamental studies of the fate, transport, and ecotoxicity of MPs and NPs in soil ecosystems. The objective of this study was therefore to develop a procedure to produce MPs and NPs from agricultural plastics (a mulch film prepared biodegradable polymer polybutyrate adipate-co-terephthalate (PBAT) and low-density PE [LDPE]), and to characterize the resultant materials. Soaking of PBAT films under cryogenic conditions promoted embrittlement, similar to what occurs through environmental weathering. LDPE and cryogenically-treated PBAT underwent mechanical milling followed by sieve fractionation into MP fractions of 840 μm, 250 μm, 106 μm, and 45 μm. The 106 μm fraction was subjected to wet grinding to produce NPs of average particle size 366.0 nm and 389.4 nm for PBAT and LDPE, respectively. A two-parameter Weibull model described the MPs' particle size distributions, while NPs possessed bimodal distributions. Size reduction did not produce any changes in the chemical properties of the plastics, except for slight depolymerization and an increase of crystallinity resulting from cryogenic treatment. This study suggests that MPs form from cutting and high-impact mechanical degradation as would occur during the tillage into soil, and that NPs form from the MP fragments in regions of relative weakness that possess lower molecular weight polymers and crystallinity.

The Sexual Double Standard in the Real World

Abstract. The sexual double standard (SDS) has traditionally been studied by examining evaluations of hypothetical targets. Although much knowledge has been gained regarding the SDS by using this methodology, the literature thus far has suffered from a lack of ecological validity. The goal of the present study was to determine whether the SDS emerged in evaluations of participants’ real-life friends and acquaintances. Participants ( n = 4,455) evaluated a single, randomly assigned male or female friend or acquaintance whose sexual history they were familiar with. Women were evaluated more negatively as their number of sexual partners increased, whereas number of partners was not related to evaluations of men. The SDS was not moderated by the closeness of the relationship between the participant and the target person.

Gender Role Violations and the Sexual Double Standard

The sexual double standard (SDS) suggests that women are evaluated negatively and men positively for engaging in similar sexual behaviors. According to social role theory, the SDS exists due to gender role structures. Consequently, perceived violations of women's sexual behavior are associated with the SDS. In addition to gender role violations of sexual behavior, two additional violations of gender roles exist: heterosexual sexual orientation norms and gender role characteristics. The current study aims to investigate whether the SDS persists for sexual orientation-violating and gender role characteristic-violating targets, and to examine which of the three gender role violations influence evaluations of others' sexual behavior. A U.S. sample of 483 participants evaluated target individuals who were either female or male, heterosexual/gay man or lesbian, feminine or masculine, and had 1 or 12 sexual partners. Results indicate that SDS persists for gender role-violating targets but is exhibited differently for targets violating heterosexual sexual orientation norms and gender role characteristics.

Characteristics of road sediment fractionated particles captured from paved surfaces, surface run-off and detention basins

This study presents the results of evaluating changes in properties of road sediment fractionated particles at the source (dry pavement), during transport (highway runoff) and after deposition (dry detention basin). A total of 38 solid particle samples were collected from paved surface, highway runoff, and from three locations within detention basins. Each sample was size-fractionated ranging from 38 μm to 1000 μm. Key results were that: (i) less than 2% of total particle mass in four vacuumed solid samples was associated with the <38 μm fraction compared to 47 to 82% in centrifuged highway runoff samples and 25% for detention basin sediments, (ii) based on number concentrations more than 90% of particles from all sources were smaller than 38 μm, (iii) the densities of fractionated particles were generally within the range from 1.5 to 2.2g/cm(3); (iv) all collected particles were predicted to resist aggregation in solution with a typical measure of surface potential, the zeta potential, typically ranging from -15 to -30 mV, (v) metal concentrations increased with decreasing particle size for vacuumed samples from the highway shoulder and parking lot, however, size dependent trends in metal concentrations were less apparent in centrifuged highway runoff samples and detention basin sediment samples; (vi) the distributions of metal mass across sieved size fractions generally followed patterns of particle mass distribution in which less than 10% of the total Cu, Pb, and Zn mass was associated with particles <38 μm; (vii) metal mass distributions tended toward increasing metal fractions in finer particle fractions along a gradient from the inlet to the outlet of the detention basins; and (viii) individual particle morphology (1 < d(p) < 10 μm) showed that particles were not smooth or spherical, clearly deviating from the assumptions typically used in estimating particle settling velocities using Stokes' Law.

Abstract 5132: Pooled shRNA screens conducted in vitro and in vivo identify genes that are essential for the growth and/or survival of human tumor cells

Identification of novel drug targets is a major challenge in cancer research. While numerous studies have identified genes that are mutated and/or amplified in cancers, the functional significance of most of these genetic alterations remains unknown. To directly identify genes that are required for the growth of human tumor cells, and that could potentially be targets for therapeutic monoclonal antibodies, we employed a custom shRNA library containing ∼13,000 shRNAs targeting 3,210 genes (∼4 shRNAs per gene) that encode cell surface or secreted proteins. Cultured tumor cells were infected with the virally-packaged shRNA library such that each shRNA (and an associated molecular barcode) was integrated into ∼200 cells. Cells that expressed shRNAs that target essential genes were progressively depleted from the population upon in vitro passage or following implantation into mice, resulting in decreased representation of those shRNAs/barcodes versus reference samples. In vitro screens were conducted in 3 colorectal cancer cell lines (HCT116, DLD1 and Colo320DM) and in NCI-H1975 lung cancer cells. About 1-3% of the genes in the library were identified as essential for tumor cell growth and/or survival in vitro. Importantly, these genes included positive controls such as PCNA that were included in the library to validate the screening procedure, as well as components of pathways that are known to control cell growth such as IGF-1R, Wnt9a, sonic hedgehog and RON. In vivo screens were performed with HCT116 and NCI-H1975 cells by implanting cells into mice immediately following shRNA integration. Representation of shRNAs versus the reference sample was assessed in small tumors (∼100 mm3) and in large tumors (1000 mm3). While we observed very few hits in small tumors, the number of hits in large tumors was greater than that observed in vitro (e.g., ∼3-fold higher for HCT116), suggesting that tumor growth in vivo is dependent on a larger set of genes than is cell growth in vitro. Interestingly, the genes that were uniquely essential in tumors versus in vitro included several that are involved in cell/cell adhesion (e.g., cadherin 24, claudin 3) and cell signaling (epidermal growth factor receptor). In summary, our shRNA screens focusing on secreted and cell surface targets have identified genes that may be essential for tumor growth, including many genes that have not previously been implicated in this process. Upon further validation, these genes could potentially serve as novel targets for therapeutic antibodies in cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5132. doi:1538-7445.AM2012-5132

Effect of self-assembled monolayers on charge injection and transport in poly(3-hexylthiophene)-based field-effect transistors at different channel length scales

Charge injection and transport in bottom-contact regioregular-poly(3-hexylthiophene) (rr-P3HT) based field-effect transistors (FETs), wherein the Au source and drain contacts are modified by self-assembled monolayers (SAMs), is reported at different channel length scales. Ultraviolet photoelectron spectroscopy is used to measure the change in metal work function upon treatment with four SAMs consisting of thiol-adsorbates of different chemical composition. Treatment of FETs with electron-poor (electron-rich) SAMs resulted in an increase (decrease) in contact metal work function because of the electron-withdrawing (-donating) tendency of the polar molecules. The change in metal work function affects charge injection and is reflected in the form of the modulation of the contact resistance, R(C). For example, R(C) decreased to 0.18 MΩ in the case of the (electron-poor) 3,5-bis-trifluoromethylbenzenethiol treated contacts from the value of 0.61 MΩ measured in the case of clean Au-contacts, whereas it increased to 0.97 MΩ in the case of the (electron-rich) 3-thiomethylthiophene treated contacts. Field-effect mobility values are observed to be affected in short-channel devices (<20 μm) but not in long-channel devices. This channel-length-dependent behavior of mobility is attributed to grain-boundary limited charge transport at longer channel lengths in these devices.

The 3'UTR of HIC mRNA improves the production of recombinant proteins in Chinese hamster ovary cells

Positive transcription elongation factor b (P-TEFb) is an important transcriptional regulator which controls 70-80% of RNA polymerase II transcription. It has been reported that the human I-mfa (inhibitor of MyoD family a) domain-containing protein (HIC) interacts with P-TEFb and that expression of HIC cDNA stimulates P-TEFb-dependent transcription. Interestingly, our recent study shows that transcriptional stimulation by HIC is predominately due to the 3' untranslated region (3'UTR) of HIC mRNA rather than its coding region. In this report, we investigate the effects of HIC 3'UTR on recombinant protein expression in mammalian cells. In transient transfections, overexpression of HIC 3'UTR stimulates transgene expression in several mammalian cell lines and significantly increases the production of human erythropoietin and interferon-gamma in Chinese hamster ovary (CHO) cells. This is the first report that demonstrates the improvement of expression of biopharmaceutical proteins by overexpressing a non-coding 3'UTR in CHO cells.

Cellular mRNA activates transcription elongation by displacing 7SK RNA

The positive transcription elongation factor P-TEFb is a pivotal regulator of gene expression in higher cells. Originally identified in Drosophila, attention was drawn to human P-TEFb by the discovery of its role as an essential cofactor for HIV-1 transcription. It is recruited to HIV transcription complexes by the viral transactivator Tat, and to cellular transcription complexes by a plethora of transcription factors. P-TEFb activity is negatively regulated by sequestration in a complex with the HEXIM proteins and 7SK RNA. The mechanism of P-TEFb release from the inhibitory complex is not known. We report that P-TEFb-dependent transcription from the HIV promoter can be stimulated by the mRNA encoding HIC, the human I-mfa domain-containing protein. The 3′-untranslated region of HIC mRNA is necessary and sufficient for this action. It forms complexes with P-TEFb and displaces 7SK RNA from the inhibitory complex in cells and cell extracts. A 314-nucleotide sequence near the 3′ end of HIC mRNA has full activity and contains a predicted structure resembling the 3′-terminal hairpin of 7SK that is critical for P-TEFb binding. This represents the first example of a cellular mRNA that can regulate transcription via P-TEFb. Our findings offer a rationale for 7SK being an RNA transcriptional regulator and suggest a practical means for enhancing gene expression.

Developmental regulators containing the I-mfa domain interact with T cyclins and Tat and modulate transcription

Positive transcription elongation factor b (P-TEFb) complexes, composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1 or T2, are engaged by many cellular transcription regulators that activate or inhibit transcription from specific promoters. The related I-mfa (inhibitor of MyoD family a) and HIC (human I-mfa-domain-containing) proteins function in myogenic differentiation and embryonic development by participating in the Wnt signaling pathway. We report that I-mfa is a novel regulator of P-TEFb. Both HIC and I-mfa interact through their homologous I-mfa domains with cyclin T1 and T2 at two binding sites. One site is the regulatory histidine-rich domain that interacts with CDK9 substrates including RNA polymerase II. The second site contains a lysine and arginine-rich motif that is highly conserved between the two T cyclins. This site overlaps and includes the previously identified Tat/TAR recognition motif of cyclin T1 required for activation of human immunodeficiency virus type 1 (HIV-1) transcription. HIC and I-mfa can serve as substrates for P-TEFb. Their I-mfa domains also bind the activation domain of HIV-1 Tat and inhibit Tat- and P-TEFb-dependent transcription from the HIV-1 promoter. This transcriptional repression is cell-type specific and can operate via Tat and cyclin T1. Genomic and sequence comparisons indicate that the I-mf and HIC genes, as well as flanking genes, diverged from a duplicated chromosomal region. Our findings link I-mfa and HIC to viral replication, and suggest that P-TEFb is modulated in the Wnt signaling pathway.

On-line monitoring of the buffer capacity of particleboard furnish by near-infrared spectroscopy

This paper reports on a study of on-line monitoring of the buffer capacity of particleboard furnish using near-infrared (NIR) spectroscopy and multivariate analysis models (chemometrics). The buffer capacity of wood furnish is known to affect the quality of polymerization and the curing rates of urea-formaldehyde (UF) resins, which may affect the mechanical properties of manufactured panel. The first phase of the study consisted of building multivariate calibration and validation models from NIR spectroscopy data to predict the buffer capacity of particleboard furnish in a laboratory environment. During this phase, a spectrometer (Ocean Optics USB2000) operating in the 550-1100 nm spectral range was evaluated. The second phase of the study took place at a North American particleboard plant over several weeks. Several multivariate calibration models were constructed and tested on-line during a four-day test period. The on-line root mean square error of prediction (RMSEP) and the coefficient of variation (CV) for buffer capacity predictions ranged from 3.45 to 0.92 and 22.4% to 5.8%, respectively.

Skin vasomotor reflex responses in two contrasting groups of autonomic failure

BACKGROUND & AIM

A variety of stimuli such as deep inspiration, isometric exercise and mental arithmetic, result in a transient vasoconstriction,mediated by sympathetic efferent nerves, in the skin of the fingers and toes of healthy controls (Skin Vasomotor Reflex: SkVR). Multiple system atrophy (MSA) and pure autonomic failure (PAF) provide contrasting models of autonomic failure. In MSA the lesion is central and preganglionic, whilst in PAF the lesion site is peripheral and postganglionic. We evaluated the SkVR in response to various stimuli in MSA and PAF, to determine differences in skin vasomotor involvement between these two patient groups.

METHODS

25 subjects (10 MSA, 7 PAF, 8 healthy controls) were studied. Baseline recordings of skin blood flow were obtained with a laser Doppler probe on the left index finger pulp and forearm. The subject then underwent a variety of stimuli with rest periods in between to reestablish baseline SkBF. These stimuli were: single deep inspiration (inspiratory gasp); mental arithmetic; bilateral leg elevation and cutaneous cold.

RESULTS

Healthy control subjects demonstrated marked SkVRs on the finger pulp to each of the stimuli of a magnitude similar to those seen in previous studies, but no SkVRs on the forearm. In MSA SkVRs to inspiratory gasp on the finger pulp were reduced relative to controls. In PAF SkVRs were reduced relative to controls or MSA. The magnitude of SkVR response to gasp and cutaneous cold in PAF was significantly less than in healthy controls. In addition, the magnitude of the response in PAF was significantly less than in MSA for inspiratory gasp.

CONCLUSIONS

PAF showed a decreased SkVR response to all 4 stimuli, the response being significantly less than controls (for inspiratory gasp and cutaneous cold) or MSA (cutaneous cold inspiratory gasp). The decreased responses in PAF may reflect the extensive postganglionic sympathetic denervation seen in this group. The measurement of SkVR may therefore provide a non-invasive aid to the differentiation of MSA and PAF.

Heat-provoked skin vasodilatation in innervated and denervated trunk dermatomes in human spinal cord injury

STUDY DESIGN

Cross-sectional, observational, controlled study.

OBJECTIVE

High spinal cord injury (SCI) results in disruption of sympathetic vasomotor control. Vasodilatation as a response to local heating is a biphasic mechanism: the first phase (neurogenic) is mediated by the axon-reflex and is modulated by activity of sympathetic nerves. Our objective was to determine whether the response to heat provocation in trunk dermatomes may provide a measure of vasomotor sympathetic function in SCI.

SETTING

National Spinal Injuries Centre, Stoke Mandeville Hospital, Buckinghamshire, UK; Autonomic Unit, The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK; Neurovascular Medicine Unit, Imperial College London at St Mary's Hospital, UK.

SUBJECTS

A total of 30 subjects were studied; 18 had chronic complete SCI (level C6-T11) and 12 were healthy controls.

METHODS

Recordings of skin blood flow (SkBF) were obtained with thermostatic laser Doppler probes placed in the upper trunk (at C4) and lower trunk (T10 or T12) dermatomes.

RESULTS

SkBF at baseline (SkBF(bas)) and SkBF at the first peak of vasodilatation (SkBF(max)) showed no significant differences between SCI and controls either in upper or lower trunk dermatomes. However, the ratio of SkBF(max)/SkBF(bas) was significantly different in lower trunk dermatomes in SCI at C6-T5 level (7.5+/-3.5 PU) compared to SCI at T6-T11 level (3.5+/-1.5 PU) (P < 0.01).

CONCLUSION

Measurement of SkBF in response to local heating may provide a safe, noninvasive method to assess integrity of sympathetic spinal pathways to the local vasculature. This may aid the classification of the SCI lesions, as the autonomic component currently is not included in the accepted American Spinal Injury Association scoring.

Geochemistry and bioavailability of metals in sediments from northern San Francisco Bay

In this study, metals (Be, Cr, Mn, Fe, Ni, Cu, Zn, Ag, Cd, Pb and Hg) in the fine-grained fraction (<63 microm) from 12 sites at different locations in northern San Francisco Bay over a year period from March 2000 to March 2001 were analyzed after acid extraction. The results showed that metal concentrations in the sediments varied from site to site, whereas some of them were found elevated with respect to the sediment of Tomales Bay, CA, which has little contamination history, indicating an enrichment of the metals in the sediment samples analyzed. Sediment toxicity and bioaccumulation evaluation by a clam species, Macoma nasuta, exposed to the sediment samples collected from the six sampling sites was carried out. The results showed that the sediment samples tested significantly reduced clam survival. Toxicity of the sediments to the clam was, in part, related to elevated metal concentrations in the sediments. In order to examine geochemistry of the metals and to understand potential correlations between metal concentrations and geochemical matrix elements of the sediments, bioavailability and toxicity of the metals, detailed analysis of metal concentrations associated with total organic carbon and the Fe-oxy-hydroxides in the sediment samples was performed. The analysis showed that sediment geochemistry appeared to influence metal bioavailability and may have important impacts on the toxicity of these metals to the clam.

The effects of water ingestion on orthostatic hypotension in two groups of chronic autonomic failure: multiple system atrophy and pure autonomic failure

BACKGROUND

Oral ingestion of water increases seated blood pressure in patients with chronic autonomic failure by mechanisms that remain unclear. As orthostatic hypotension is common in chronic autonomic failure, and is not always adequately controlled by medication, the potential benefits of water ingestion on standing blood pressure were studied in two types of autonomic failure: multiple system atrophy (MSA), in which the lesion is central and pre-ganglionic, and pure autonomic failure (PAF), in which the lesion is post-ganglionic.

METHODS

In 14 patients with autonomic failure (seven PAF and seven MSA) standing blood pressure and heart rate were measured before, and 15 and 35 minutes after ingestion of 480 ml distilled water. Patients remained seated for 15 minutes after water ingestion, with beat to beat cardiovascular indices measured with the Portapres II device with subsequent Modelflow analysis.

RESULTS

Standing prior to water ingestion caused a significant fall in blood pressure in all patients. After water ingestion there was a rise in seated blood pressure. Seated and standing blood pressure at 15 and 35 minutes after water ingestion was significantly higher than before water, with an improvement in orthostatic symptoms. The time to first significant rise in seated blood pressure occurred at 5 minutes post water ingestion in PAF and at 13 minutes in MSA. These increases were accompanied by increases in total peripheral resistance, reaching significance by 5 minutes in PAF and 13 minutes in MSA. There were no significant changes in cardiac output, stroke volume, or ejection fraction.

CONCLUSIONS

Water is thus beneficial in improving standing BP in AF, acting within 15 minutes in both MSA and PAF. The earlier onset of the pressor effect in PAF may reflect the differing lesion site and underlying pathophysiology between these conditions.

Water drinking in the management of orthostatic intolerance due to orthostatic hypotension, vasovagal syncope and the postural tachycardia syndrome

Water drinking recently has been shown to raise blood pressure in normal subjects and in patients with autonomic failure who have orthostatic hypotension. However, in normal young subjects, ingestion of approximately 500 ml has no pressor effect; but in older subjects there is an increase in blood pressure. An even greater rise in blood pressure occurs in cases with autonomic failure. The possible mechanisms responsible for the pressor response to water include neural and humoral factors; fluid redistribution also needs to be considered. This review will concentrate on the water pressor response in normal subjects and different groups of patients with autonomic diseases who have orthostatic intolerance, on the mechanisms that could be involved, and on whether this pressor response may be used in the management of orthostatic hypotension, vasovagal syncope and the postural tachycardia syndrome.

The human I-mfa domain-containing protein, HIC, interacts with cyclin T1 and modulates P-TEFb-dependent transcription

Positive transcription elongation factor b (P-TEFb) hyperphosphorylates the carboxy-terminal domain of RNA polymerase II, permitting productive transcriptional elongation. The cyclin T1 subunit of P-TEFb engages cellular transcription factors as well as the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. To identify potential P-TEFb regulators, we conducted a yeast two-hybrid screen with cyclin T1 as bait. Among the proteins isolated was the human I-mfa domain-containing protein (HIC). HIC has been reported to modulate expression from both cellular and viral promoters via its C-terminal cysteine-rich domain, which is similar to the inhibitor of MyoD family a (I-mfa) protein. We show that HIC binds cyclin T1 in yeast and mammalian cells and that it interacts with intact P-TEFb in mammalian cell extracts. The interaction involves the I-mfa domain of HIC and the regulatory histidine-rich region of cyclin T1. HIC also binds Tat via its I-mfa domain, although the sequence requirements are different. HIC colocalizes with cyclin T1 in nuclear speckle regions and with Tat in the nucleolus. Expression of the HIC cDNA modulates Tat transactivation of the HIV-1 long terminal repeat (LTR) in a cell type-specific fashion. It is mildly inhibitory in CEM cells but stimulates gene expression in HeLa, COS, and NIH 3T3 cells. The isolated I-mfa domain acts as a dominant negative inhibitor. Activation of the HIV-1 LTR by HIC in NIH 3T3 cells occurs at the RNA level and is mediated by direct interactions with P-TEFb.

The growth factor granulin interacts with cyclin T1 and modulates P-TEFb-dependent transcription

Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.

Internal poverty and teen pregnancy

The subjects for the present study were drawn from the female students who participated in the National Education Longitudinal Study (NELS) initial eighth-grade data collection. Adolescent females who later became pregnant were matched on race, birth month, and birth year with adolescent females who did not report a pregnancy. The study examined selected predictor variables from the baseline 1988 wave of data in relation to the outcome variable of pregnancy status. Results indicated a statistically significant difference in locus of control between those females who later became pregnant and those who later did not experience a pregnancy during adolescence. Those who later became pregnant were much more likely to have an external locus of control (p = .0001). Females who later became pregnant were also more likely to have a poorer sense of personal efficacy (p = .0001). Finally, females who later experienced a teen pregnancy had more traditional occupational expectations (p = .006) and lower educational expectations (p = .001) than did those who did not later report a teen pregnancy.

Clonogenic analysis reveals reserve stem cells in postnatal mammals: I. Pluripotent mesenchymal stem cells

Clonal populations of lineage-uncommitted pluripotent mesenchymal stem cells have been identified in prenatal avians and rodents. These cells reside in the connective tissue matrices of many organs and tissues. They demonstrate extended capabilities for self-renewal and the ability to differentiate into multiple separate tissues within the mesodermal germ line. This study was designed to determine whether such cells are present in the connective tissues of postnatal mammals. This report describes a cell clone derived by isolation from postnatal rat connective tissues, cryopreservation, extended propagation, and serial dilution clonogenic analysis. In the undifferentiated state, this clone demonstrates a high nuclear-to-cytoplasmic ratio and extended capacity for self-renewal. Subsequent morphological, histochemical, and immunochemical analysis after the induction of differentiation revealed phenotypic markers characteristic of multiple cell types of mesodermal origin, such as skeletal muscle, smooth muscle, fat cells, cartilage, and bone. These results indicate that this clone consists of pluripotent mesenchymal stem cells. This report demonstrates that clonal populations of reserve stem cells are present in mammals after birth. Potential roles for such cells in the maintenance, repair, and regeneration of mesodermal tissues are discussed.

Contaminant interactions with geosorbent organic matter: insights drawn from polymer sciences

This is a state-of-science review of interrelationships between the sorption/desorption behaviors and chemical structures of natural organic matter (NOM) matrices associated with soils, sediments and aquifer materials. It identifies similarities between these behavior-property interrelationships for natural geosorbents and those for synthetic organic polymers. It then invokes, with appropriate restrictions and modifications, several structure-function relationships that have been developed for synthetic polymers to explain the behavior of NOM matrices with respect to the sorption and desorption of hydrophobic organic contaminants (HOCs). Previous research regarding HOC sorption and desorption by different types of NOM and by synthetic polymers is summarized, and research requirements for further refinement of the NOM-polymer analogy are examined. The discussion focuses on structural and compositional heterogeneities that exist at the particle and aggregate scale, a scale at which homogeneity is commonly, and often improperly, assumed in the development of contaminant fate and transport models.

The effect of lower-extremity position on cerebrospinal fluid pressures

OBJECTIVE

To determine the effects of lower-extremity positioning on cerebrospinal fluid opening pressure (CSFp). The authors believed that during lumbar puncture (LP), CSFp does not meaningfully decrease when the lower extremities are extended from flexion, as is often suggested.

METHODS

In a convenience sample of adult patients who clinically required LP in an urban emergency department, three sequential CSFp measurements were obtained in either sequence A (knee, hip, and neck flexion [90 degrees ], then extension, then flexion) or sequence B (extension, flexion, then extension) prior to CSF withdrawal. The neck was flexed at 30 degrees when the lower extremities were flexed, while the thoracolumbar spine was kept in the neutral position for all measurements.

RESULTS

Nineteen patients were studied in each sequence. Although variable, overall within-patient changes between positions were not clinically meaningful. Mean and 95% confidence intervals (95% CIs) for the decrease in CSFp from position 1 to position 3 (same position) were 0.2 cm H(2)O (1.7%) and 0.9 to -0.6 cm H(2)O (6% to -2.7%), respectively. Changing from flexion to extension decreased pressure measurements by a mean of 0.9 cm H(2)O (2.5%) [95% CI = 2.1 to -0.1 cm H(2)O (7.6% to -2.4%)]. Changing from extension to flexion increased CSFp by a mean of 1.1 cm H(2)O (6.1%) [95% CI = 0.2 to 2.0 cm H(2)O (1.3% to 11.5%)], a statistically but not clinically meaningful change.

CONCLUSIONS

Changing lower-extremity position did not meaningfully change mean CSFp. These data do not support the common suggestion that extending the lower extremities during LP meaningfully decreases CSF opening pressures.

Sympathetic activity and baroreflex sensitivity in young women taking oral contraceptives

BACKGROUND

We tested sympathetic and cardiovagal baroreflex sensitivity during the placebo or "low-hormone" phase (LH) and 2 to 3 weeks later during the "high-hormone" phase (HH) of oral contraceptive (OC) use in 9 women.

METHODS AND RESULTS

Sympathetic baroreflex sensitivity was assessed by intravenous doses of sodium nitroprusside and phenylephrine and defined as the slope relating muscle sympathetic nerve activity (by microneurography) and diastolic blood pressure. Cardiovagal baroreflex sensitivity was defined as the slope relating R-R interval and systolic blood pressure. No difference was observed for resting muscle sympathetic nerve activity or plasma norepinephrine levels. However, sympathetic baroreflex sensitivity was greater and mean arterial pressure was higher during the LH than in the HH phase. Similarly, cardiovagal baroreflex sensitivity was greater in the LH than in the HH phase.

CONCLUSIONS

Sympathetic and cardiovagal baroreflex sensitivities change during the 28-day course of OC use. Furthermore, changes in baroreflex sensitivity with OC differ from changes in baroreflex sensitivity during the normal menstrual cycle.

Supercritical fluid extraction of 2,4,6-trichloroanisole from cork stoppers

2,4,6-Trichloroanisole (TCA) is the compound most often associated with cork taint in wines and has been shown to have a very low sensory threshold ( approximately 5 ng/L in wine). A supercritical fluid extraction (SFE) method for TCA in bark cork stoppers was developed with quantification via gas chromatography-mass spectrometry with selected ion monitoring. Supercritical carbon dioxide functioned as the extracting solvent, and temperature and pressure were optimized for the extraction. The method was validated using the stable isotope (2)H(5)-TCA as the internal standard. Recovery of TCA from spiked corks was found to be within 1-4% of the theoretical concentration with a coefficient of variation ranging from 2.6 to 9.7%. TCA levels in corks pulled from wines described as tainted by experienced judges ranged from 0.13 to 2.11 microg/g of cork. The SFE procedure offers a rapid, quantitative, nearly solvent-free, and automated method for the extraction of TCA from complex solid matrices such as cork.

Influence of the menstrual cycle on sympathetic activity, baroreflex sensitivity, and vascular transduction in young women

BACKGROUND

Our goal was to test sympathetic and cardiovagal baroreflex sensitivity and the transduction of sympathetic traffic into vascular resistance during the early follicular (EF) and midluteal (ML) phases of the menstrual cycle.

METHODS AND RESULTS

Sympathetic baroreflex sensitivity was assessed by lowering and raising blood pressure with intravenous bolus doses of sodium nitroprusside and phenylephrine. It was defined as the slope relating muscle sympathetic nerve activity (MSNA; determined by microneurography) and diastolic blood pressure. Cardiovagal baroreflex sensitivity was defined as the slope relating R-R interval and systolic blood pressure. Vascular transduction was evaluated during ischemic handgrip exercise and postexercise ischemia, and it was defined as the slope relating MSNA and calf vascular resistance (determined by plethysmography). Resting MSNA (EF, 1170+/-151 U/min; ML, 2252+/-251 U/min; P<0.001) and plasma norepinephrine levels (EF, 240+/-21 pg/mL; ML, 294+/-25 pg/mL; P=0. 025) were significantly higher in the ML than in the EF phase. Furthermore, sympathetic baroreflex sensitivity was greater during the ML than the EF phase in every subject (MSNA/diastolic blood pressure slopes: EF, -4.15; FL, -5.42; P=0.005). No significant differences in cardiovagal baroreflex sensitivity or vascular transduction were observed.

CONCLUSIONS

The present study suggests that the hormonal fluctuations that occur during the normal menstrual cycle may alter sympathetic outflow but not the transduction of sympathetic activity into vascular resistance.

Rectal leiomyosarcoma diagnosed by endoscopic ultrasonography

A 67 year-old man was admitted to the Tainan Municipal Hospital due to a protruding mass, usually noted during defecation. Digital examination revealed a single, smooth, large mass over the rectum, occupying almost the entire lumen. Colonoscopy, barium enema, and computed tomography (CT) demonstrated a submucosal tumor of the rectum. Endoscopic ultrasound (EUS) study showed that the tumor originated from the muscle layer. Based on the size, margin and echogenicity of the mass, a malignant neoplasm, probably leiomyosarcoma, was diagnosed. Post-operative histologic examination confirmed that the resected tumor was leiomyosarcoma. Existing ancillary procedures like colonoscopy, abdominal CT, magnetic resonance image (MRI), and barium enema are neither reliable nor accurate in locating which layer the lesion originates. Colonoscopic biopsy is disappointing since submucosal tumor is usually inaccessible. EUS study can provide us with a more distinct image with regards to tumor origin, size, margin and echogenicity. This report emphasizes the important role of EUS in the pre-operative diagnosis of submucosal tumors of the rectum. Furthermore, this tool can aid the surgeons whether wide excision or an abdomino-perineal resection should be performed.

Human and rodent transcription elongation factor P-TEFb: interactions with human immunodeficiency virus type 1 tat and carboxy-terminal domain substrate

The human immunodeficiency virus type 1 transcriptional regulator Tat increases the efficiency of elongation, and complexes containing the cellular kinase CDK9 have been implicated in this process. CDK9 is part of the Tat-associated kinase TAK and of the elongation factor P-TEFb (positive transcription elongation factor-b), which consists minimally of CDK9 and cyclin T. TAK and P-TEFb are both able to phosphorylate the carboxy-terminal domain (CTD) of RNA polymerase II, but their relationships to one another and to the stimulation of elongation by Tat are not well characterized. Here we demonstrate that human cyclin T1 (but not cyclin T2) interacts with the activation domain of Tat and is a component of TAK as well as of P-TEFb. Rodent (mouse and Chinese hamster) cyclin T1 is defective in Tat binding and transactivation, but hamster CDK9 interacts with human cyclin T1 to give active TAK in hybrid cells containing human chromosome 12. Although TAK is phosphorylated on both serine and threonine residues, it specifically phosphorylates serine 5 in the CTD heptamer. TAK is found in the nuclear and cytoplasmic fractions of human cells as a large complex (approximately 950 kDa). Magnesium or zinc ions are required for the association of Tat with the kinase. We suggest a model in which Tat first interacts with P-TEFb to form the TAK complex that engages with TAR RNA and the elongating transcription complex, resulting in hyperphosphorylation of the CTD on serine 5 residues.

Testing and evaluation of wheelchair caster assemblies subjected to dynamic crash loading

Wheelchair designs based upon loads applied quasi-statically during normal mobility use are apt to be inadequate to handle the increased level of dynamic crash forces that may be encountered when using the wheelchair as a motor vehicle seat. The purpose of this study was to characterize the integrity of wheelchair caster assemblies under simulated crash conditions. This study utilized dynamic drop (DD) testing, with loading levels and rates adjusted to match those found previously in sled impact testing and computer crash simulations. The results verify that current caster assembly designs may not be able to withstand forces associated with a crash. Five of seven evaluated caster assemblies failed when loaded to 8,007 N, or less, at loading rates seen in sled testing. DD testing used in this study is a valuable tool that can be used in the design of transport wheelchair components.

Potential interaction involving warfarin and ritonavir

OBJECTIVE

To report an unexpected decrease in warfarin effect following the addition of ritonavir to the medication regimen.

CASE SUMMARY

A 27-year-old patient with advanced HIV taking warfarin for an inferior vena cava thrombus was started on ritonavir, clarithromycin, and zidovudine. The international normalized ratio (INR) decreased over a period of weeks after the addition of ritonavir, clarithromycin, and zidovudine to the drug therapy regimen. The warfarin dosage was almost doubled in order to maintain a therapeutic INR. Months later, when ritonavir alone was discontinued, the INR rose rapidly and the warfarin dose requirements decreased significantly.

DISCUSSION

Potential interactions between warfarin and the protease inhibitors are described in the literature. Ritonavir has been shown to be a potent inhibitor of CYP3A4, an enzyme responsible for warfarin metabolism. Potentiation of warfarin effect and subsequent decrease in the warfarin dosage requirement was anticipated following ritonavir administration; however, the opposite occurred. The mechanism of the potential interaction between warfarin and ritonavir is not known, and may represent a complex, multidrug interaction. The paradoxical decrease in the INR is particularly intriguing.

CONCLUSIONS

Frequent, careful monitoring of warfarin is recommended when ritonavir therapy is initiated or discontinued in a patient taking warfarin. The potential for either an increase or decrease in the INR should be anticipated.

Collaboration of a public child welfare agency and a school of social work: a clinical group supervision project

As an addition to the growing literature on school of social work/child welfare agency collaborations, this article describes a clinical group supervision arrangement between Children and Youth Services of Delaware County, Pennsylvania, and the master of social work program at Widener University's Center for Social Work Education in Chester, Pennsylvania. Six students who were also employees of the department received clinical group supervision every other week by a faculty member of the center. The process of initiating the group, the supervision issues that emerged, the articulation and application of a model of child-centered family treatment, and preliminary results from the use of a Skill-Level Self-Rating scale are presented and discussed.

Airway management in dental anaesthesia

Ninety patients were allocated randomly to three groups for airway maintenance during paediatric outpatient dental extraction: laryngeal mask airway, nasal mask with nasopharyngeal airway, or nasal mask alone. Surgical access was better with the laryngeal mask. Airway maintenance was easier with the laryngeal mask than the nasopharyngeal airway, and both were better than nasal mask alone. No patient became hypoxic with the laryngeal mask, five patients became hypoxic with the nasal mask and two with the nasopharyngeal airway at corresponding periods, although the differences were not statistically significant. The laryngeal mask airway is recommended for paediatric outpatient dental anaesthesia.

Effects of orthodontics on the facial profile: a comparison of changes during nonextraction and four premolar extraction treatment

Cephalometric radiographs were used to examine soft tissue profiles of 198 orthodontic patients treated with full fixed appliances without extraction of any permanent teeth. Records were selected at random from five sources: cases treated by a Tweed Foundation instructor using the Tweed technique, patients treated with the Begg appliance, patients treated in one of two different practices with pretorqued, preangulated edgewise appliances, and patients treated in two stages with a functional appliance followed by full fixed edgewise appliances. The criteria for selection of cases and the methods of data collection were designed to allow comparisons with data collected by Drobocky and Smith on patients treated with extraction of four first premolars. Although the mean value of soft tissue changes were smaller in the nonextraction patients, the variability of these changes were generally as great as in the four premolar extraction cases. In addition, the percentage of undesirable facial changes was similar in the extraction and nonextraction samples. The results provide additional evidence that it is simplistic and incorrect to blame undesirable facial esthetics after orthodontic treatment on the extraction of premolars.

Channel fluctuations induced by membrane attack complex C5B-9

The assembly of complement (C) components C5b-9 in membranes results in the formation of transmembrane lesions. The C9 component has been shown to be mainly responsible for formation of the ultrastructurally visible tubules associated with C5b-9 complexes. Several studies have disputed the role of C9 polymerization in C-mediated cytolysis on the grounds that C5b-9 lyses cells in the absence of tubular formation. Here, C5b-9 complexes were reconstituted into high-impedance planar lipid bilayers and shown to form channels which are heterogenous in size. The smallest channels had unitary conductances of 15 picoSiemens (pS) in 0.1 M NaCl. The closing of these channels showed voltage-dependence at membrane potentials exceeding 40 mV. These channels were more cation-selective, with K+ ions being favored over Na+. The 15-pS channels described here are much smaller than the channels attributed previously to either C5b-9 or polymerized C9 complexes but resemble channels formed by the C9b fragment, which does not polymerize into tubules. These results indicate that C5b-9 complexes are capable of damaging membranes by forming initially small ion channels which then aggregate in the membrane to form tubular lesions with much larger conductances. Like C5b-9, C5b-8 also increased membrane permeability. However, this increase in membrane conductance could not be resolved into single channels, suggesting that C5b-8 may induce membrane leakiness by perturbing the packing of membrane lipids, whereas addition of C9 results in authentic production of ion channels.

An evaluation of combining thiopentone and etomidate for the induction of anaesthesia

The characteristics of three combinations of thiopentone and etomidate [in the ratios of thiopentone (mg):etomidate (mg) of 5:1, 13:1 and 25:1] have been compared with the individual agents alone for the induction of anaesthesia. The incidence of pain on injection and abnormal movements was less with the combination containing the highest ratio of thiopentone to etomidate, when compared to etomidate alone. The mixtures did not otherwise confer any advantages over the individual agents.

Comparison of basic data for the National Survey of Residential Group Care Facilities: 1966-1982

Major findings from this analysis of the data gathered in preparation for the 1966 and 1981 surveys of children's residential group care facilities are as follows below. In the field of residential care of pregnant adolescents, it appears that, despite an increase in the number of births to adolescent mothers since 1966, the preferred mode of serving this population is no longer residential group care. While there has been a small increase (6 facilities) in the number of residential facilities for pregnant adolescents that operate under public auspices, the 49% decrease in facilities under private auspices is the real indicator of the direction of residential services to pregnant adolescents since 1965. In the Child Welfare Stream, the most notable change between 1965 and 1981 was the decrease in the relative proportion of residential group care facilities for dependent, neglected, or abused children and youth. Overall, child welfare facilities accounted for 55% of all residential facilities listed for survey in 1965; in 1981 this percentage had fallen to 37%. As in 1965 the Child Welfare Stream was dominated by the private sector in 1981, with 83% of all child welfare facilities operating under private auspices. This pattern was found for most of the 50 individual states as well. In the Juvenile Justice Stream, the overall increase of 154% in the number of residential facilities since the 1965 listing is due in part to a notable increase in the number of private facilities in this stream of care. Although the majority of juvenile justice facilities are still public, there has been an increase of 17% since 1965 in the proportion of facilities under private auspices. An even greater increase in total number of facilities than was seen in the Juvenile Justice Stream is seen in the mental health field between 1965 and 1981. There were almost four times as many residential mental health facilities listed for survey in 1981 as in 1965. From representing about one-eighth of the total number of all residential group care facilities for children and youth with special problems or needs, the Mental Health Stream increased to a quarter of all such facilities by 1981. As in the earlier study, the Mental Health Stream was dominated by the private sector in 1981. The proportion of mental health facilities under private auspices had increased by 16% since 1965, indicating an even greater involvement of the private sector in the delivery of residential mental health services to children and youth.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein-mediated intermembrane contact facilitates fusion of lipid vesicles with planar bilayers

Fusion of phospholipid vesicles with planar bilayer membranes occurs provided there is an intermembrane contact, which can be mediated by phospholipid-binding proteins, even in the absence of calcium. The firm attachment phase is then followed by the osmotically-driven fusion. These results show that hydrophobic proteins (not necessarily Ca2+-binding proteins) may enhance fusion by promoting contact of membranes. Such proteins may operate synergistically with Ca2+ to reduce the threshold concentration of Ca2+ needed for fusion of biological membranes. Protein-mediated intermembrane contact resulting in fusion may play a crucial role in the regulation and catalysis of biological fusion events.

Role for mouse macrophage IgG Fc receptor as ligand-dependent ion channel

The interaction of ligands with the mouse macrophage Fc receptor which binds IgG2b and IgG1 immune complexes (FcR gamma 2b/gamma 1) triggers phagocytosis and secretion of various mediators of inflammation. FcR gamma 2b/gamma 1 has been purified using a monoclonal anti-FcR antibody, 2.4G2, and seems to be an integral membrane glycoprotein of molecular weight (Mr) 47,000-60,000 (ref. 6). Monoclonal antibody 2.4G2 is suitable as a tool for functional studies of FcR because it binds to a functional site of the receptor and induces cellular responses that are normally associated with the occupied receptor. We reported previously that binding of ligands to the macrophage FcR resulted in Na+/K+ ion fluxes through the plasma membrane, and that similar ion fluxes were observed in proteoliposomes containing reconstituted FcR. We have now incorporated FcR into planar lipid bilayers and report here that FcR gamma 2b/gamma 1 forms ligand-dependent cation-selective ion channels, with a conductance of 60 pS in 1 M KCl and an average open channel lifetime of 250 ms. The conductance decays to baseline levels within a few minutes. These results suggest a receptor-ionophore model for the signalling of phagocytosis and inflammatory responses.