Dielectric travelling wave antennas for directional light emission.

We present a combined experimental and numerical study of the far-field emission properties of optical travelling wave antennas made from low-loss dielectric materials. The antennas considered here are composed of two simple building blocks, a director and a reflector, deposited on a glass substrate. Colloidal quantum dots placed in the feed gap between the two elements serve as internal light source. The emission profile of the antenna is mainly formed by the director while the reflector suppresses backward emission. Systematic studies of the director dimensions as well as variation of antenna material show that the effective refractive index of the director primarily governs the far-field emission pattern. Below cut off, i.e., if the director's effective refractive index is smaller than the refractive index of the substrate, the main lobe results from leaky wave emission along the director. In contrast, if the director supports a guided mode, the emission predominately originates from the end facet of the director.

Modulation of disease severity in cystic fibrosis transmembrane conductance regulator deficient mice by a secondary genetic factor.

Mice that have been made deficient for the cystic fibrosis transmembrane conductance regulator (Cftr) usually die of intestinal obstruction. We have created Cftr-deficient mice and demonstrate prolonged survival among backcross and intercross progeny with different inbred strains, suggesting that modulation of disease severity is genetically determined. A genome scan showed that the major modifier locus maps near the centromere of mouse chromosome 7. Electrophysiological studies on mice with prolonged survival show that the partial rectification of Cl- and Na+ ion transport abnormalities can be explained in part by up-regulation of a calcium-activated Cl- conductance. Identification of modifier genes in our Cftr(m1HSC)/Cftr(m1HSC) mice should provide important insight into the heterogeneous disease presentation observed among CF patients.

Collective effects in second-harmonic generation from split-ring-resonator arrays.

Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.

The emergence of a highly transmissible lineage of cbl+ Pseudomonas (Burkholderia) cepacia causing CF centre epidemics in North America and Britain.

The rapid increase in Pseudomonas (Burkholderia) cepacia infection in cystic fibrosis (CF) patients suggests epidemic transmission, but the degree of transmissibility remains controversial as conflicting conclusions have been drawn from studies at different CF centres. This report provides the first DNA sequence-based documentation of a divergent evolutionary lineage of P. cepacia associated with CF centre epidemics in North America (Toronto) and Europe (Edinburgh). The involved epidemic clone encoded and expressed novel cable (Cbl) pili that bind to CF mucin. The sequence of the cblA pilin subunit gene carried by the epidemic isolates proved to be invariant. Although it remains to be determined how many distinct, highly transmissible lineages exist, our results provide both a DNA sequence and chromosomal fingerprint that can be used to screen for one such particularly infectious, transatlantic clone.

Reversal of coherently controlled ultrafast photocurrents by band mixing in undoped GaAs quantum wells.

It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.

Radioimmunoassay of human intestinal goblet cell mucin. Investigation of mucus from different organs and species.

We have developed a double-antibody radioimmunoassay for the quantitative measurement of human goblet cell mucin (GCM) in order to study intestinal mucus in human and other species. The assay used 3H-labeled mucin as the antigen, rabbit antisera, and sheep anti-rabbit IgG antisera as the second antibody. A number of applications of the assay were investigated. A survey of human tissues revealed that mucins of the rectum, colon, and small intestine had identical affinity for the rabbit antibody, whereas lung eyelid conjunctiva, esophagus, and stomach reacted less strongly. GCM concentration ranged from 1.9 to 14 microgram mucin protein/mg tissue protein in the small and large intestine, respectively. The radioimmunoassay was also found to be useful as a marker during the isolation of GCM from human ileal extracts, where it indicated that a 10,000-fold purification had been achieved. Antigenic determinants of the mucin did not rely upon ABH blood group-specific terminal sugars in oligosaccharide chains. A comparison of mucins among various species revealed a partial species specificity of the GCM antibody. Human GCM cross-reacted with dog, monkey, and rabbit mucins, but not with mucins of rat, pig, toad, and oyster. Organ distributions of cross-reactive mucins in rabbit tissues indicated a pattern that was qualitatively similar to that seen in human tissues. Possible implications of these findings for autoimmune diseases are briefly discussed.

Binding of Pseudomonas cepacia to normal human intestinal mucin and respiratory mucin from patients with cystic fibrosis.

Although not as prevalent as Pseudomonas aeruginosa, Pseudomonas cepacia is another opportunistic pathogen which colonizes the lungs of at least some patients with cystic fibrosis. A subgroup of these patients exhibits the "cepacia syndrome", i.e., a rapid clinical deterioration and death within one year. To investigate potential early sites of bacterial attachment, we have measured the specific binding of P. cepacia isolates from cystic fibrosis (CF) sputa to both CF and non-CF mucins purified from respiratory and intestinal secretions, respectively. As shown in microtiter binding assays, clinical isolates from 19/22 patients were found to bind to both mucins, with the highest specific binding exhibited by isolates from eight patients, seven of whom later died with the cepacia syndrome. No differences were observed in the binding capacity of the two (CF versus non-CF) mucins. Binding was specific, saturable, and not influenced by tetramethylurea, a disruptor of hydrophobic associations. Individual sugars were ineffective as hapten inhibitors, as were several lectins. Mucins treated by reduction/alkylation or chloroform/methanol extraction showed enhanced bacterial binding, findings which were attributed to exposure of underlying binding sites. Deglycosylation procedures indicated that mucin receptors for P. cepacia include N-acetylglucosamine and N-acetylgalactosamine, probably linked together as part of core oligosaccharide structures. P. cepacia isolates also bound to buccal epithelial cells, and mucin partially inhibited the binding of those isolates of P. cepacia that also had the ability to bind to mucin. We speculate that specific binding of P. cepacia to secreted mucins may be an early step in the pathogenesis of the cepacia syndrome.

Binding of nonmucoid Pseudomonas aeruginosa to normal human intestinal mucin and respiratory mucin from patients with cystic fibrosis.

Lung infections due to Pseudomonas aeruginosa and Pseudomonas cepacia are common in patients with cystic fibrosis. Initial colonization is due to nonmucoid P. aeruginosa, while later mucoid variants emerge and are associated with chronic infection. P. cepacia colonization tends to be more prevalent in older patients. The present study was conducted to discover whether highly purified mucins (from cystic fibrosis sputum and control intestinal secretions) exhibited specific binding of nonmucoid P. aeruginosa. In vitro solid phase microtiter binding assays (with or without a blocking agent) as well as solution phase assays were conducted. Bacteria bound to both mucins via bacterial pili, but no differences in binding capacity were noted between the mucins. Unlike P. cepacia (described in the accompanying manuscript) there was also no preferential binding of P. aeruginosa to mucins versus bovine serum albumin, casein, gelatin, or a host of structurally unrelated proteins and glycoproteins. Carbohydrate hapten inhibition studies did not suggest the existence of specific mucin carbohydrate receptors for P. aeruginosa. In solid phase assays a low concentration (0.05 M) of tetramethylurea abolished P. aeruginosa bacterial binding to both mucins as well as to BSA, whereas in solution phase assays mucin binding to bacteria was not completely disrupted by tetramethylurea. Specific monoclonal antipilus antibodies did not inhibit binding to a greater extent than did Fab fragments of normal mouse IgG. Binding of strains PAO1 and PAK (and isolated PAK pili) to buccal epithelial cells was not influenced by the presence of mucin in binding assay mixtures. Our findings do not support the widely held notion that specific mucin receptors are responsible for the attachment of P. aeruginosa pili, nor do they support the idea that there is a competitive interference by mucins of bacterial binding to respiratory cells. In patients with cystic fibrosis, it would seem unlikely therefore that initial colonization of the lungs by P. aeruginosa is due to a 'selective tropism' of these bacteria for respiratory mucin.

Mucin degradation in the intestine.

Rat intestinal mucin was labelled biologically by intraperitoneal injection of radioactive amino acids and monosaccharides 3--6 h prior to killing, followed by isolation and purification of the mucin from mucosal scrapings. The labelled product was then introduced into intestinal segments of rats under ether anesthesia for periods up to 3 h, removed by washing and assessed for evidence of degradation. In segments containing the pancreatic ducts the total mucin precipitable by cetyltrimethylammonium bromide fell from 80% to 5% in 3 h. At 3 h, chromatography on Sephadex G-100 and Sepharose 4B revealed multiple products, including very small molecular weight fragments deficient in carbohydrate label. With the introduction of neomycin sulfate into the segments to reduce bacterial growth, only two products were found, one corresponding in size to the original mucin and one somewhat smaller, although still in excess of 200,000 daltons. These products occurred independently of the presence of the pancreatic ducts in the segments, and in chronically pancreatectomized rats. The smaller product could not be produced by incubation with trypsin or elastase. Both products were altered antigenically as compared with the original mucin. Both products also retained the same ratio of carbohydrate and protein label as the original. It is concluded that mucins undergo early degradative changes in the intestine which do not involve deglycosylation but which involve partial loss of antigenicity and a fall in molecular weight. The pancreas is not responsible for these changes.

Calcium binding to intestinal goblet cell mucin.

1. Binding of Ca-2+ to goblet cell mucin of rat small intestine was studied using equilibrium dialysis against 0.01 M Tris/HCl buffer (pH 7.4) and tracer amounts of 45-CaCl2. Binding was found to reach saturation at a Ca free -2+ concentration of 0.1--1.0 mM, to be independent of temperature (4-37 degrees C), and to increase with increasing pH (5.0-8.7). At low concentrations of Ca free -2+ (smaller than 0.03 mM) the binding curve was sigmoidal, suggesting positive cooperativity of binding sites and a possible change in the tertiary structure of the mucin. Binding was markedly reduced, and sigmoidicity abolished, by removal of sialic acid from the mucin, or by adding 0.14 M NaCl to the dialysis medium. This latter finding suggests that, in vivo, other cations would compete for Ca-2+ binding ligands. 2. Under conditions mimicking those used for binding studies, CaCl2 (10- minus 5 M) was found to cause a small increase (0.03 units) in the absorbance of mucin solutions, especially in the ultraviolet region, possibly indicating increased light scattering. No change in the solubility of the mucin was observed after the addition of CaCl2 (10- minus 6-10- minus 4 M). A significant decrease in viscosity of the mucin was noted, however, with the addition of CaCl2 (10- minus 6-10- minus 2 M). Together with the binding data, these findings suggested that during binding, Ca-2+ combines with negative charges on goblet cell mucin (especially those of sialic acid carboxyl groups) and induces contraction or folding of the macromolecule which promotes cooperative cation binding. No evidence was obtained to suggest that CaCl2 caused precipitation, polymerization or gelation of the mucin in 0.01 M Tris/HCl.?

A serine, threonine and proline-rich region near the carboxyl-terminus of a rat intestinal mucin peptide.

Further sequencing of a cDNA encoding the C-terminal region of a rat intestinal mucin peptide reveals a region corresponding to 258 amino acids enriched in serine, threonine and proline, but no typical mucin-like tandem repeat structures. Between this region and a previously described stretch of 4.5 degenerate S,T,P-rich tandem repeats, there is a 42 amino acid cysteine-rich segment. The discontinuity of cysteine-rich and S,T,P-rich areas near the C-terminus has not been observed in other mammalian mucin structures reported to date.

Vibrio cholerae metalloproteinase degrades intestinal mucin and facilitates enterotoxin-induced secretion from rat intestine.

Mucin secretion in situ from rat intestinal loops was promoted more effectively by dialysed crude cholera filtrate than by an equivalent amount of purified enterotoxin. The filtrate could be rendered inactive by incubation with mixed gangliosides or passage through a GM1-affinity column, which indicated that the secretory action of the filtrate depended upon its enterotoxin component. In an effort to explain the greater potency of the filtrate, we established the presence of a metalloproteinase in the filtrate and demonstrated that this enzyme was capable of degrading purified rat intestinal mucin. Sufficient degradation occurred to cause a substantial decrease in viscosity (57% in 120 min). Biochemical analysis of the mucin before and after exposure to filtrate revealed a rise in the combined percentage of serine, threonine and proline (53-58%), suggesting that poorly glycosylated areas (which are less abundant in these amino acids) were being partly removed from the mucin. The carbohydrate composition was essentially unaltered. Inhibition of the filtrate metalloproteinase by Zincov and alpha 2-macroglobulin significantly (P less than 0.005) reduced the ability of cholera filtrate to degrade mucin or to stimulate mucin secretion from rat intestinal slices in vitro. Purified cholera enterotoxin added to enterotoxin-depleted filtrate was a more potent secretagogue (secretory stimulant) in intestinal loops than an equivalent amount of enterotoxin alone. We therefore propose that mucin secretion induced by cholera filtrate is caused by cholera enterotoxin, but that degradation of the protective epithelial mucus layer by a constituent metalloproteinase may assist the toxin by allowing increased access to mucosal GM1 receptor sites.

The carboxyl-terminal sequence of rat intestinal mucin RMuc3 contains a putative transmembrane region and two EGF-like motifs.

A 3' RACE technique was used to establish the nucleotide sequence encoding the C-terminal 379 amino acids of rat intestinal Muc3. Unlike the C-terminus of Muc2 and many secretory mucins, Muc3 contains two EGF motifs and a putative transmembrane domain. The mRNA for rat Muc3 is 7.5-8.0 kb.

Cloning of the cDNA for a rat intestinal Na+/dicarboxylate cotransporter reveals partial sequence homology with a rat intestinal mucin.

In this report we present the full-length cDNA and deduced 587 amino acid sequence of a putative rat intestinal Na+/dicarboxylate cotransporter. It shows sequence and structural similarity to a rabbit renal Na+/dicarboxylate cotransporter. An unexpected fining was the presence of a C-terminal transmembrane region that is homologous with an 87 amino acid hydrophobic region of a rat intestinal mucin, M2. Mucin-related sequences in transporter proteins have not been described before.

Inhibition of mucin secretion in a colonic adenocarcinoma cell line by DIDS and potassium channel blockers.

The factors which influence the exocytosis of mucins are not well characterized. Since the physical properties of mucins may be affected significantly by the co-secretion of electrolytes and water, we studied the relationship between ion movement and mucin secretion in T84 cells, a human colonic adenocarcinoma cell line which has been well characterized with respect to apical chloride secretion. Secretion of mucin was assessed by immunoassay of mucin appearing in the medium within 30 min of stimulation. Cells were grown on plastic in DMEM/Ham's F12 medium and experiments were carried out at 70% confluence. Mucin secretion was stimulated by the calcium ionophore A23187, or A23187 plus vasoactive intestinal polypeptide. Stimulated mucin secretion was not affected by loop diuretics (furosemide (1 x 10(-3) M) or bumetanide (1 x 10(-4) M)), with or without the addition of ouabain (5 x 10(-5) M) and amiloride (1 x 10(-5) M), making it unlikely that transcellular chloride movements in necessary for mucin secretion. However, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; (1 x 10(-5) and 5 x 10(-5) M) and three potassium channel blockers BaCl2 (1 x 10(-3) and 5 x 10(-3) M), tetraethylammonium chloride (1 x 10(-2) M) and quinine (5 x 10(-4) M) inhibited mucin secretion. A DIDS-sensitive chloride channel or chloride/bicarbonate exchanger and a Ca2(+)-dependent potassium channel may play important roles in mucin secretion. Since plasma membranes are sparingly permeable to DIDS, the DIDS-sensitive site is likely to be on the apical plasma membrane, perhaps at an initiation locus for exocytosis.

Radiation inactivation of human intestinal mucin: determination of the size of the functional antigenic unit.

Previously we have shown that the major antigenic determinant of human intestinal mucin is associated with its glycopeptide monomers and not the 118 kDa 'link' component. In the present study, the size and nature of the functional unit containing the antigenic determinant has been assessed by radiation inactivation and immunological assays. Increasing doses of radiation led to a monoexponential decay in antigenic reactivity due to a progressive loss of antigenic determinants. From three independent mucin preparations, a value of 78500 +/- 7000 was determined for the Mr of the functional antigenic unit. Prolonged pronase digestion of native mucin released large degraded glycopeptide monomers containing all the mucin carbohydrate, and low molecular weight peptides. The antigenicity of the glycopeptides decreased with digestion but could not be recovered in the peptide fractions, suggesting that determinants were released and destroyed by the enzyme. Treatment of native mucin with trifluoromethanesulphonic acid caused a major loss of carbohydrate (approx. 70%), but the protein component was unchanged in amino acid profile and remained antigenic. Subsequent thiol reduction, however, abolished the antigenicity of the deglycosylated mucin. We conclude that antigenicity is associated with a non-glycosylated segment of the peptide backbone of the glycopeptides and that a large functional unit of Mr 78500 which is stabilized by disulphide bonds is important for full antigenic activity.

Electromagnetic field structure and normal mode coupling in photonic crystal nanocavities.

The electromagnetic field of a high-quality photonic crystal nanocavity is computed using the finite difference time domain method. It is shown that a separatrix occurs in the local energy flux discriminating between predominantly near and far field components. Placing a two-level atom into the cavity leads to characteristic field modifications and normal-mode splitting in the transmission spectra.

Robust population inversion by polarization selective pulsed excitation.

The coherent state preparation and control of single quantum systems is an important prerequisite for the implementation of functional quantum devices. Prominent examples for such systems are semiconductor quantum dots, which exhibit a fine structure split single exciton state and a V-type three level structure, given by a common ground state and two distinguishable and separately excitable transitions. In this work we introduce a novel concept for the preparation of a robust inversion by the sequential excitation in a V-type system via distinguishable paths.

Radiosurgery for brain metastases: is whole brain radiotherapy necessary?

PURPOSE: Because whole brain radiotherapy (WBRT) may cause dementia in long-term survivors, selected patients with brain metastases may benefit from initial treatment with radiosurgery (RS) alone reserving WBRT for salvage as needed. We reviewed results of RS +/- WBRT in patients with newly diagnosed brain metastasis to provide background for a prospective trial. METHODS AND MATERIALS: Patients with single or multiple brain metastases managed initially with RS alone vs. RS + WBRT (62 vs. 43 patients) from 1991 through February 1997 were retrospectively reviewed. The use of upfront WBRT depended on physician preference and referral patterns. Survival, freedom from progression (FFP) endpoints, and brain control allowing for successful salvage therapy were measured from the date of diagnosis of brain metastases. Actuarial curves were estimated using the Kaplan-Meier method. Analyses to adjust for known prognostic factors were performed using the Cox proportional hazards model (CPHM) stratified by primary site. RESULTS: Survival and local FFP were the same for RS alone vs. RS + WBRT (median survival 11.3 vs. 11.1 months and 1-year local FFP by patient 71% vs. 79%, respectively). Brain FFP (scoring new metastases and/or local failure) was significantly worse for RS alone vs. RS + WBRT (28% vs. 69% at 1 year; CPHM adjustedp = 0.03 and hazard ratio = 0.476). However, brain control allowing for successful salvage of a first failure was not significantly different for RS alone vs. RS + WBRT (62% vs. 73% at 1 year; CPHM adjusted p = 0.56). CONCLUSIONS: The omission of WBRT in the initial management of patients treated with RS for up to 4 brain metastases does not appear to compromise survival or intracranial control allowing for salvage therapy as indicated. A randomized trial of RS vs. RS + WBRT is needed to assess survival, quality of life, and cost in good-prognosis patients with newly diagnosed brain metastases.

Isoelectric focusing of serum in cystic fibrosis: failure to distinguish between homozygote and heterozygote sera.

Thin-layer isoelectric focusing was performed on samples of sera from patients with Cystic Fibrosis, siblings and obligate heterozygotes (parents), and children without cystic fibrosis (controls). The protein band with an isoelectric point of pH 5.48, previously reported to be absent in homozygote cystic fibrosis sera, was found to have a pI of 5.25. It was present in approximately one-half of the homozygote and heterozygote sera tested, and absent from 18 percent of control sera. The presence of this band is not therefore a reliable marker for the normal gene, and cannot be used to identify the heterozygous carrier for cystic fibrosis.