Probing the surfaces of core-shell and hollow nanoparticles by solvent relaxation NMR

Measurement of the spin-spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core-shell (titania-silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character.

Influence of vancomycin minimum inhibitory concentration on the outcome of methicillin-susceptible Staphylococcus aureus left-sided infective endocarditis treated with antistaphylococcal β-lactam antibiotics: a prospective cohort study by the International Collaboration on Endocarditis

OBJECTIVES

Left-sided methicillin-susceptible Staphylococcus aureus (MSSA) endocarditis treated with cloxacillin has a poorer prognosis when the vancomycin minimum inhibitory concentration (MIC) is ≥1.5 mg/L. We aimed to validate this using the International Collaboration on Endocarditis cohort and to analyse whether specific genetic characteristics were associated with a high vancomycin MIC (≥1.5 mg/L) phenotype.

METHODS

All patients with left-sided MSSA infective endocarditis treated with antistaphylococcal β-lactam antibiotics between 2000 and 2006 with available isolates were included. Vancomycin MIC was determined by Etest as either high (≥1.5 mg/L) or low (<1.5 mg/L). Isolates underwent spa typing to infer clonal complexes and multiplex PCR for identifying virulence genes. Univariate analysis was performed to evaluate the association between in-hospital and 1-year mortality, and vancomycin MIC phenotype.

RESULTS

Sixty-two cases met the inclusion criteria. Vancomycin MIC was low in 28 cases (45%) and high in 34 cases (55%). No significant differences in patient demographic data or characteristics of infection were observed between patients with infective endocarditis due to high and low vancomycin MIC isolates. Isolates with high and low vancomycin MIC had similar distributions of virulence genes and clonal lineages. In-hospital and 1-year mortality did not differ significantly between the two groups (32% (9/28) vs. 27% (9/34), p 0.780; and 43% (12/28) vs. 29% (10/34), p 0.298, for low and high vancomycin MIC respectively).

CONCLUSIONS

In this international cohort of patients with left-sided MSSA endocarditis treated with antistaphylococcal β-lactams, vancomycin MIC phenotype was not associated with patient demographics, clinical outcome or virulence gene repertoire.

Report on World Workshops on Oral Medicine (WWOM) IV and V: research themes and citation impact: WWOM VI steering committee

The first World Workshop on Oral Medicine (WWOM) was held in 1988. The portfolio has continued to expand in scope and impact over the past 26 years. Five World Workshops were conducted between 1988 and 2010, focusing on creation of systematic reviews in biomedicine and health care of importance to the international oral medicine community. WWOM VI was conducted in April 2014 and further extended this modeling. This most recent Workshop also fostered creation of the inaugural joint meeting between the American Academy of Oral Medicine and the European Association of Oral Medicine, together with The British Society for Oral Medicine and the Oral Medicine Academy of Australasia. The goal of the WWOM portfolio is to strategically enhance international oral medicine research, education, and clinical practice. To this end, this report summarizes subject areas for WWOM IV (2004) and research recommendations for WWOM V (2010), as well as citation metrics relative to publications from these two conferences. The information is designed to provide research and clinical context for key issues in oral medicine as delineated by the WWOM portfolio over the past 10 years, as well as for projected outcomes of WWOM VI over the next 12 months.

Repeat endocarditis: analysis of risk factors based on the International Collaboration on Endocarditis - Prospective Cohort Study

Repeat episodes of infective endocarditis (IE) can occur in patients who survive an initial episode. We analysed risk factors and 1-year mortality of patients with repeat IE. We considered 1874 patients enrolled in the International Collaboration on Endocarditis - Prospective Cohort Study between January 2000 and December 2006 (ICE-PCS) who had definite native or prosthetic valve IE and 1-year follow-up. Multivariable analysis was used to determine risk factors for repeat IE and 1-year mortality. Of 1874 patients, 1783 (95.2%) had single-episode IE and 91 (4.8%) had repeat IE: 74/91 (81%) with new infection and 17/91 (19%) with presumed relapse. On bivariate analysis, repeat IE was associated with haemodialysis (p 0.002), HIV (p 0.009), injection drug use (IDU) (p < 0.001), Staphylococcus aureus IE (p 0.003), healthcare acquisition (p 0.006) and previous IE before ICE enrolment (p 0.001). On adjusted analysis, independent risk factors were haemodialysis (OR, 2.5; 95% CI, 1.2-5.3), IDU (OR, 2.9; 95% CI, 1.6-5.4), previous IE (OR, 2.8; 95% CI, 1.5-5.1) and living in the North American region (OR, 1.9; 95% CI, 1.1-3.4). Patients with repeat IE had higher 1-year mortality than those with single-episode IE (p 0.003). Repeat IE is associated with IDU, previous IE and haemodialysis. Clinicians should be aware of these risk factors in order to recognize patients who are at risk of repeat IE.

Summary of: Oral health, dental prophylaxis and catheter related bloodstream infections in home parenteral nutrition patients: results of a UK survey and cohort study

BACKGROUND

Concern that some catheter related bloodstream infections (CRBSI) arise from dental treatment in home parenteral nutrition (HPN) patients results in recommendation of antibiotic prophylaxis. Clinical guideline 64 is widely recognised and observed. There is a lack of consistent guidance for other patient groups viewed at risk from procedural bacteraemia.

METHODS

1. An email survey of the British Association for Parenteral and Enteral Nutrition (BAPEN) HPN group, requesting physicians' opinions, observations and practises relating to oral health and CRBSI prevention; 2. Comparison of oral health parameters and dental treatment in relation to patient reported 12 month CVC infection history, using chi-square analysis to assess associations in 52 HPN patients.

RESULTS

1. Sixty-eight percent of the UK HPN Group responded. Fifty percent linked oral health/dental treatment with the possibility of CRBSI, 39% were unsure. Sixty-one percent had recommended parenteral prophylactic antibiotics (82% IV, 18% IM), mainly following the historic infective endocarditis (IE) dental prophylaxis guidelines. Infection with streptococci, prevotella and fusobacteria caused most concern. Amoxicillin, metronidazole, co-amoxyclav and gentamycin were the most prescribed antibiotics. Thirty-six percent might delay HPN if oral health was poor; 57% had recommended dental examination and 25% dental extractions, to prevent or treat CRBSI. 2. Associations between patient recalled CVC infection and their current dental status, the interval since dental treatment or the prophylaxis received over the previous 12 months did not achieve significance.

CONCLUSIONS

Opinion varies among UK HPN providers on the role of dental treatment and oral health in CRBSI and on prescribing prophylactic antibiotics for dental treatment. Prophylaxis guidance specific to this patient group is required.

Intracellular regions of potassium channels: Kv2.1 and heag

Intracellular regions of voltage-gated potassium channels often comprise the largest part of the channel protein, and yet the functional role of these regions is not fully understood. For the Kv2.1 channel, although there are differences in activation kinetics between rat and human channels, there are, for instance, no differences in movement of the S4 region between the two channels, and indeed our mutagenesis studies have identified interacting residues in both the N- and C -terminal intracellular regions that are responsible for these functional effects. Furthermore, using FRET with fluorescent-tagged Kv2.1 channels, we have shown movement of the C-termini relative to the N-termini during activation. Such interactions and movements of the intracellular regions of the channel appear to form part of the channel gating machinery. Heag1 and heag2 channels also display differing activation properties, despite their considerable homology. By a chimeric approach, we have shown that these differences in activation kinetics are determined by multiple interacting regions in the N-terminus and membrane-spanning regions. Furthermore, alanine mutations of many residues in the C-terminal cyclic nucleotide binding domain affect activation kinetics. The data again suggest interacting regions between N- and C- termini that participate in the conformational changes during channel activation. Using a mass-spectrometry approach, we have identified alpha-tubulin and a heat shock protein as binding to the C-terminus of the heag2 channel, and alpha-tubulin itself has functional effects on channel activation kinetics. Clearly, the intracellular regions of these ion channels (and most likely many other ion channels too) are important regions in determining channel function.

Desquamative gingivitis: A sign of mucocutaneous disorders-a review

Desquamative gingivitis is a clinical term to describe red, painful, glazed and friable gingivae which may be a manifestation of some mucocutaneous conditions such as lichen planus or the vesiculobullous disorders. It is important to be aware of this rare clinical entity so as to distinguish desquamative gingivitis from plaque induced gingivitis which is an extremely common condition, easily recognized and treated daily by the dental practitioner. This article gives an overview of desquamative gingivitis, its presentation, the possible causes, diagnosis and treatment. Early recognition of these lesions may prevent delayed diagnosis and inappropriate treatment of potentially serious dermatological diseases.

Amalgam-tattoo-associated oral lichenoid lesion

We report on a lichenoid reaction that developed in association with amalgam particles within an amalgam tattoo of the oral mucosa.

First Report of Lethal Yellowing Disease of Coconut Palms Caused by Phytoplasma on Nevis Island

Coconuts (Cocos nucifera) are an important small-holder's crop in many tropical countries and are used to enhance esthetics of coastal areas. Lethal yellowing (LY) is the single most important plant disease affecting the coconut industry in Jamaica. It affects many palm species in Jamaica, Florida, and Guatemala. This coconut disease was first recorded in Grand Cayman Island in 1834 and Jamaica in 1884. Symptoms of LY disease include premature nut fall, necrosis of the inflorescence, yellowing of the leaves, and defoliation. Thirty-eight coconut palms displaying symptoms indicative of LY disease were sampled in April, 2005 at several locations in Nevis. Immature leaf tissues (leaf bases adjacent to the apical meristem) and nondestructive (boring with a bit and braces) samples were collected from disease and healthy control coconut trees. DNA was extracted (2). The first round of polymerase chain reaction (PCR) with phytoplasma universal primer pair P1/P7 (1,3) resulted in an rDNA fragment of 1.8 kb, and a subsequent nested PCR using LY16-23Sr/LY16Sf primers yielded an amplicon of 1.74 kb (4). Purified product was cloned for sequencing. Sequences obtained were analyzed with Vector NTI Software Suite. The sequence of LYN 18-3 was entered in Genbank and Accession No. DQ378279 was assigned. LYN 18-3 has approximately 99% homology with LY Phytoplasma U18747 from Florida (Manila palm [Veitchia merrillii]). The disease-associated phytoplasma was reliably detected in immature tissues and trunk phloem at the onset of foliar symptoms in palms by PCR. On the basis of the results obtained from this study, it is clear that LY phytoplasma (16SrIV group) was found in the samples collected from Nevis. To our knowledge, this is the first report on lethal yellowing disease in Nevis. References: (1) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53 1991. (2) J. J. Doyle and J. L. Doyle. Focus 12:13, 1990. (3) N. A. Harrison et al. Ann. Appl. Biol. 141:183, 2002. (4) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.

The role of ultrasound in monitoring reconstruction of mandibular continuity defects using osteogenic protein-1 (rhOP-1)

Introducing bone bioengineering concepts in craniofacial surgery demands development of novel imaging strategies, which overcome the shortcomings of radiography such as exposure to ionizing radiation. This study is aimed to investigate the usefulness of ultrasonography (US) in monitoring reconstruction of continuity osteoperiosteal mandibular defects in sheep using rhOP-1. The study was conducted on six adult sheep in which a critical size defect was created at the body of the mandible and was reconstructed using rhOP-1 with type-I collagen as a carrier. Ultrasound images were used to assess onset of bone formation, contour, and surface topography. The results were then compared to corresponding plain radiographs and to post-mortem observations. US showed bone union in all the subjects that concurred with radiographic and post-mortem examinations. US was superior to plain radiography in monitoring early events of ossification. However, it was relatively less efficient in describing the contour of the newly formed bone. It was possible to describe the pattern of bone formation and the dynamic changes in contour and surface topography via US during the follow-up period. In experienced hands, ultrasonography can offer valuable information about bone healing comparable with those obtained by plain radiography. US may replace plain radiography in becoming a routinely used tool for monitoring bone healing in selected sites of the craniofacial skeleton.

The roles of intracellular regions in the activation of voltage-dependent potassium channels

The involvement of the transmembrane regions S2, S3 and S4 in the activation of potassium channels by depolarization has been well clarified. However, a role of the intracellular regions in channel function is emerging. Here we review recent evidence for the roles of intracellular regions in the functioning of members of two families of channels. The Kv2.1 potassium channel, a member of the voltage activated Kv family, has long intracellular regions. By mutagenesis studies and expression in oocytes, we identify residues in both the N- and C-terminal regions that contribute to determining activation kinetics of this channel. It seems that the C-terminus wraps around the N-terminus and interacts with it functionally. The voltage-activated ether-a-go-go (eag) channels also have long intracellular regions. Despite considerable homology, eag1 and eag2 channels display different activation kinetics. By making chimeras between these channels and again expressing in oocytes, we show that residues in both the N-terminal region and the membrane-spanning region are involved in determining these differences in activation kinetics. The intracellular N- and C-terminal regions are likely to continue to prove fertile regions in future investigations into the functioning of ion channels.

Molecular identification and characterisation of the human eag2 potassium channel

We report the molecular cloning from foetal brain of the human potassium channel heag2. The cDNA encodes a protein of 988 amino acids, 73% identical to heag1. Heag2 is expressed in the brain, but is also found in a range of tissues including skeletal muscle. In oocytes, the channel is a non-inactivating outward rectifier, with dependence of activation rate on holding potential. Compared with heag1, the conductance-voltage curve for heag2 was shifted to the left, the voltage sensitivity was less, activation kinetics were different, and the sensitivity to terfenadine was lower. The heag2 channel may have important physiological roles.

Coupling of voltage-dependent potassium channel inactivation and oxidoreductase active site of Kvbeta subunits

The accessory beta subunits of voltage-dependent potassium (Kv) channels form tetramers arranged with 4-fold rotational symmetry like the membrane-integral and pore-forming alpha subunits (Gulbis, J. M., Mann, S., and MacKinnon, R. (1999) Cell. 90, 943-952). The crystal structure of the Kvbeta2 subunit shows that Kvbeta subunits are oxidoreductase enzymes containing an active site composed of conserved catalytic residues, a nicotinamide (NADPH)-cofactor, and a substrate binding site. Also, Kvbeta subunits with an N-terminal inactivating domain like Kvbeta1.1 (Rettig, J., Heinemann, S. H., Wunder, F., Lorra, C., Parcej, D. N., Dolly, O., and Pongs, O. (1994) Nature 369, 289-294) and Kvbeta3.1 (Heinemann, S. H., Rettig, J., Graack, H. R., and Pongs, O. (1996) J. Physiol. (Lond.) 493, 625-633) confer rapid N-type inactivation to otherwise non-inactivating channels. Here we show by a combination of structural modeling and electrophysiological characterization of structure-based mutations that changes in Kvbeta oxidoreductase activity may markedly influence the gating mode of Kv channels. Amino acid substitutions of the putative catalytic residues in the Kvbeta1.1 oxidoreductase active site attenuate the inactivating activity of Kvbeta1.1 in Xenopus oocytes. Conversely, mutating the substrate binding domain and/or the cofactor binding domain rescues the failure of Kvbeta3.1 to confer rapid inactivation to Kv1.5 channels in Xenopus oocytes. We propose that Kvbeta oxidoreductase activity couples Kv channel inactivation to cellular redox regulation.

NHS Direct: issues for education, management and research

The NHS Plan (Department of Health (DoH), 2000) specifically highlights the role of NHS Direct in its vision of a health service designed around the patient. Despite this, the new nurse-led service has come under critical attack. NHS Direct is in the process of developing an evidence base to underpin its practice. It is recognized that telephone management skills are important clinical skills and while decision support computer software can help elicit an appropriate client history, the interpersonal skills necessary to establish a professional telephone relationship are commensurate with the suitability of the appropriate education programme. This article will explore the ramifications of NHS Direct for curriculum development and evaluation. Factors such as skill mix, career pathways, recruitment and research and development will also be discussed. In a previous article the implications of NHS Direct for practice were examined (Glasper et al, 2000).

Detection of Helicobacter pylori DNA in recurrent aphthous stomatitis tissue by PCR

Helicobacter pylori is recognised as being an aetiological agent of chronic active gastritis and peptic ulcer disease and has been associated with an increased risk of gastric cancer. The natural reservoir for H. pylori is unknown, although the oral cavity has been the focus of much attention in this respect. Given the histological similarities between gastric and oral ulceration, it seemed prudent to investigate a possible association between H. pylori and recurrent aphthous stomatitis (RAS). In this study, the potential involvement of H. pylori in the aetiology of RAS was investigated using the polymerase chain reaction (PCR). Biopsies from 28 RAS patients were analysed, in addition to 20 oral lichen planus (OLP) and 13 normal biopsies that were used as controls. Genomic DNA was extracted from biopsies, and confirmation of successful extraction of PCR-amplifiable DNA was achieved by carrying out PCR on each DNA sample with nested primers specific for the human beta-haemoglobin gene. PCR identification of H. pylori was carried out using a primer pair specific for the H. pylori 16S ribosomal RNA (rRNA) gene. Two rounds of PCR were carried out to amplify a 295-bp product, and the identity of amplified products was confirmed by DNA sequencing. H. pylori DNA was detected in 3 of 28 (11%) RAS samples but not in any of 20 OLP and 13 normal samples. These results do not support a definitive aetiological role for H. pylori in RAS, although the possibility that H. pylori may be involved in a small proportion of RAS cases cannot be excluded.

In vitro resistance to thrombin-induced platelet microbicidal protein in isolates of Staphylococcus aureus from endocarditis patients correlates with an intravascular device source

Platelet microbicidal proteins (PMPs) are small antimicrobial peptides secreted by mammalian platelets. In vitro resistance of Staphylococcus aureus strains to PMPs correlates with more extensive disease in experimental infective endocarditis (IE). To determine whether this same relationship exists in human S. aureus IE, we evaluated the in vitro PMP susceptibility phenotype of isolates from 58 prospectively-identified patients with definite S. aureus IE. On multivariate analyses, patients with S. aureus IE complicating an infected intravascular device were significantly more likely to have IE caused by a PMP-resistant strain (P=.0193). No correlations were detected between in vitro PMP resistance among S. aureus strains and the severity of human IE. This work supports the concept that in vitro PMP resistance in clinical S. aureus strains is associated with important clinical characteristics of S. aureus endovascular infections in vivo.

NHS Direct: examining the challenges for nursing practice

This article examines the impact of the launch of NHS Direct which was part of the Government's vision for a modern and dependable NHS. In particular, the challenges for nursing practice are detailed within a healthcare strategy which seeks to provide fast access primary health care to the whole population. The strengths and weaknesses of NHS Direct are discussed and its interface with other agencies explored. As NHS Direct will cover the whole of England by October 2000, the evidence to underpin its effectiveness must be considered in the light of media criticisms which indicate that the quality of advice given to callers is sometimes less than optimum.

The role of allergy in oral mucosal diseases

We retrospectively assessed the prevalence of positive results to cutaneous patch testing, and the relevance of exclusion of identified allergens in the disease process, in 1252 patients with oral mucosal diseases presenting to the Department of Oral Medicine in Glasgow Dental Hospital and School and referred to the Contact Dermatitis Investigation Unit in Glasgow Royal Infirmary. The prevalence of patch-test positivity in each disease cohort was compared with that in 100 control volunteers. Patients with oral mucosal diseases were significantly more likely to have demonstrable hypersensitivity to food additives, especially benzoic acid, and perfumes and flavourings, especially cinnamaldehyde, than controls, and avoidance therapy caused improvement in the majority. Patch testing and the resultant avoidance therapy are useful adjuncts in the management of oral mucosal diseases.

Local movement in the S2 region of the voltage-gated potassium channel hKv2.1 studied using cysteine mutagenesis

The positively charged S4 region of voltage-dependent potassium channels moves outward during depolarization, leading to channel opening, but possible movement of the negatively charged S2 region may be more complex. Here we have studied possible movement of the S2 region of the slowly activating human voltage-dependent potassium channel hKv2.1. For this, cysteine mutants in the S2 region were expressed in Xenopus oocytes by injection of cRNA. Whole-cell currents were measured using the two-electrode voltage-clamp technique, and the effect of the membrane-impermeable cysteine-binding reagent parachloromercuribenzenesulfonate (PCMBS) was studied. For mutant S223C (located just outside the membrane in the S2 region), PCMBS inhibited currents and caused faster deactivation of tail currents. The time course of reactivity of PCMBS on tail current amplitudes was faster at more negative holding potentials. There was no effect of PCMBS on potassium channel currents for mutants D225C, N226C, A230C, and V232C. These data suggest that residue S223 is exposed to the extracellular phase at normal resting potentials, making it accessible to PCMBS, but upon depolarization there is a conformational change, making it less accessible, possibly by a local rather than global movement of S2 residues into the membrane. Voltage-dependent movements of nearby residues could also explain the results.

Regulation of cloned cardiac L-type calcium channels by cGMP-dependent protein kinase

We have studied the effect of 8-bromo-cyclic GMP (8-Br-cGMP) on cloned cardiac L-type calcium channel currents to determine the site and mechanism of action underlying the functional effect. Rabbit cardiac alpha(1C) subunit, in the presence or absence of beta(1) subunit (rabbit skeletal muscle) or beta(2) subunit (rat cardiac/brain), was expressed in Xenopus oocytes, and two-electrode voltage-clamp recordings were made 2 or 3 days later. Application of 8-Br-cGMP caused decreases in calcium channel currents in cells expressing the alpha(1C) subunit, whether or not a beta subunit was co-expressed. No inhibition of currents by 8-Br-cGMP was observed in the presence of the protein kinase G inhibitor KT5823. Substitutions of serine residues by alanine were made at residues Ser(533) and Ser(1371) on the alpha(1C) subunit. As for wild type, the mutant S1371A exhibited inhibition of calcium channel currents by 8-Br-cGMP, whereas no effect of 8-Br-cGMP was observed for mutant S533A. Inhibition of calcium currents by 8-Br-cGMP was also observed in the additional presence of the alpha(2)delta subunit for wild type channels but not for the mutant S533A. These results indicate that cGMP causes inhibition of L-type calcium channel currents by phosphorylation of the alpha(1C) subunit at position Ser(533) via the action of protein kinase G.

Oral staphylococcal mucositis: A new clinical entity in orofacial granulomatosis and Crohn's disease

OBJECTIVE

Orofacial granulomatosis and the oral manifestations of Crohn's disease comprise many clinical features, of which stomatitis is one. The purpose of this study was to establish a role for Staphylococcus aureus in mucositis affecting some patients with orofacial granulomatosis or oral Crohn's disease.

STUDY DESIGN

Four patients (2 with orofacial granulomatosis and 2 with oral Crohn's disease), from a total of 450 patients examined over 10 years, had stomatitis involving the entire oral mucosa, from which S aureus was cultured by the oral rinse technique. These patients were treated with flucloxacillin or erythromycin.

RESULTS

A heavy growth of S aureus was isolated from the mouth of each patient. All 4 patients responded to treatment with flucloxacillin or erythromycin.

CONCLUSIONS

S aureus is a potential cause of panstomatitis in patients with orofacial granulomatosis or Crohn's disease. This infection responds rapidly to antimicrobial treatment.

Lack of association between Streptococcus oralis and recurrent aphthous stomatitis

In the present study, the potential involvement of Streptococcus oralis in the aetiology of recurrent aphthous stomatitis (RAS) was investigated using the polymerase chain reaction (PCR). Biopsies from 28 RAS patients were analysed, in addition to 20 oral lichen planus (OLP) and 13 normal biopsies that were used as controls. PCR was carried out using a primer pair that targets the D-alanine:D-alanine ligase gene and detects DNA from both S. oralis and the closely related species Streptococcus mitis. Discrimination between these two species was achieved by digestion of PCR products with the restriction endonucleases HaeIII and HindIII, which both give distinct restriction profiles for each species. S. oralis DNA was detected in 8 of 28 (29%) RAS samples, 10 of 20 (50%) OLP samples and 6 of 13 (46%) normal samples. These results suggest that S. oralis is not of primary aetiological significance in RAS.

Effect of cysteine substitutions on the topology of the S4 segment of the Shaker potassium channel: implications for molecular models of gating

1. The gating properties of voltage-gated potassium channels are largely determined by the amino acid sequence of their S4 segments. To investigate the nature of S4 movement during gating, we introduced single cysteines into the S4 segment of the Shaker potassium channel and expressed the mutants in Xenopus oocytes. We then measured the conductance-voltage (g-V) relationships and the rate and the voltage dependence of movement of the engineered cysteines, using p-chloromercuribenzene sulphonate (pCMBS) as a probe. 2. Mutation of charged residues at positions 362, 365 and 368, but not the uncharged residues (positions 360, 361, 363, 364 and 366), to cysteines shifted the g-V relationships to more positive potentials. Mutant channels in which cysteines replaced the charged residues at positions 362 and 365 (R362C and R365C) reacted faster with pCMBS than those in which cysteines were introduced in place of uncharged residues at positions 360 and 361 (I360C and L361C). Furthermore, the R365C mutant channel reacted with pCMBS even at hyperpolarised (-120 mV) potentials. Currents expressed by the doubly mutated R365S/V367C and R368S/V367C channels, but not the singly mutated V367C channel, were inhibited by pCMBS. Moreover, the R368C mutant channel was also affected by pCMBS. 3. Voltage dependence of block by pCMBS (2 min exposure) was steeper for L366C than for L361C and V363C mutant channels (effective charge 2.19, 1. 41 and 1.45, respectively). The voltage dependence of the pCMBS effect was also shifted to more depolarising potentials the deeper in the membrane the position of the residue mutated to cysteine (voltages for half-maximal effect -107, -94 and -73 mV for positions 361, 363 and 366, respectively). 4. Our data show firstly that charge-neutralising mutations in S4 alter the topology of this region such that the membrane-spanning portion of S4 is reduced. Secondly, our data for the other mutant channels suggest that S4 might move in at least two sequential steps, and can move up to its maximal limit even at the resting potential of the cell.

The effects of oxidizing and cysteine-reactive reagents on the inward rectifier potassium channels Kir2.3 and Kir1.1

The inwardly rectifying potassium channel Kir2.3 possesses extracellular cysteine residues at positions 113, 140, and 145, as well as at position 79 near the outer membrane boundary. In this study, we have investigated the roles of these extracellular cysteine residues in mediating inhibition of the Kir2.3 channel by the cysteine-reactive reagents para-chloromercuribenzenesulphonate (PCMBS) and thimerosal, and the oxidizing agent hydrogen peroxide (H2O2). We have also compared the effects of these reagents with those on Kir1.1 channels (which do not possess cysteine residues equivalent to 140 and 79 in Kir2.3 channels). Mutant channels were made in which cysteine residues were mutated to serine by site-directed mutagenesis. Wild-type or mutant cRNA was injected into Xenopus oocytes and voltage-clamp recordings made 1-2 days later. Wild-type Kir2.3 currents were significantly inhibited by PCMBS, thimerosal and H2O2. Currents for mutants Kir2.3 C79S and C140S were also inhibited by PCMBS, thimerosal and H2O2. These mutations affected the time course of inhibition by all three reagents. For PCMBS, a slow component of inhibition was absent for the C79S mutation, and a fast component was absent for C140S. For the double mutation C79S/C140S, PCMBS no longer had any effect. For thimerosal, there was a slower time course for C140S, a faster time course for C79S, and a delayed onset for C79S/C140S. For H2O2, the main effect was a delayed onset for the double mutant. The reducing agent dithiothreitol (DTT) reversed the inhibition by both PCMBS and thimerosal of wild-type and mutant currents, but not the inhibition due to H2O2. Finally, wild-type Kir1.1 currents were not significantly inhibited by the applications of either PCMBS or thimerosal, while H2O2 produced small inhibition. The results taken together indicate that inhibition by the cysteine-reactive reagent PCMBS is mediated through cysteine residues 79 and 140 in Kir2.3 channels, with C79 mediating a slow component of inhibition and C140 a faster component, and that both residues are extracellularly exposed. The data indicate that these two cysteine residues are also main sites for inhibition by thimerosal and H2O2 but, unlike for PCMBS, an additional non-extracellular inhibitory site(s) must also be involved.

Conserved extracellular cysteine residues in the inwardly rectifying potassium channel Kir2.3 are required for function but not expression in the membrane

The mouse potassium channel Kir2.3 possesses conserved extracellular cysteine residues at positions 113 and 145. We have investigated the role of these cysteines in structure/function and membrane trafficking. Cysteine to serine mutations resulted in the absence of potassium currents in oocytes and co-expression of these mutants with wild-type channel showed a dominant negative inhibition of wild-type currents. FLAG-tagged channels expressed in oocytes were detected in the cell membrane by anti-FLAG antibody for wild-type and mutant channels. In vitro translation using the reticulocyte lysate system showed that mutation of these residues did not affect processing nor insertion into membranes. Cysteine residues at 113 and 145 are therefore required for function of the Kir2.3 channel but not for processing into the cell membrane; disulfide bonds between subunits are unlikely.

Functional and molecular aspects of voltage-gated K+ channel beta subunits

Voltage-gated potassium channels (Kv) of the Shaker-related superfamily are assembled from membrane-integrated alpha subunits and auxiliary beta subunits. The beta subunits may increase Kv channel surface expression and/or confer A-type behavior to noninactivating Kv channels in heterologous expression systems. The interaction of Kv alpha and Kv beta subunits depends on the presence or absence of several domains including the amino-terminal N-type inactivating and NIP domains and the Kv alpha and Kv beta binding domains. Loss of function of Kv beta 1.1 subunits leads to a reduction of A-type Kv channel activity in hippocampal and striatal neurons of knock-out mice. This reduction may be correlated with altered cognition and motor control in the knock-out mice.

Detection of serum antibodies against cytomegalovirus, varicella zoster virus and human herpesvirus 6 in patients with recurrent aphthous stomatitis

There has recently been renewed interest in the possible role of viruses in recurrent aphthous stomatitis (RAS). In this study, sera from 22 patients with RAS, 24 patients with oral lichen planus (OLP) and 15 healthy controls were screened for IgG and IgM class antibodies to human cytomegalovirus (HCMV), varicella zoster virus (VZV) and human herpesvirus 6 (HHV-6). Commercially available ELISA and immunofluorescence kits were employed. There were no significant differences in the prevalence of IgG antibodies to HCMV, VZV or HHV-6 among the three patient groups. Similarly, there were no significant differences between the prevalence of HCMV and VZV IgM antibodies among RAS patients and controls. However, specific HHV-6 IgM was detected in 21 (95%) of the RAS patients and 17 (71%) of the lichen planus patients compared with 8 (53%) of the healthy controls. This difference between RAS patients and controls was statistically significant (P<0.01). These results do not support an aetiological role for HCMV or VZV in RAS but suggest possible involvement of HHV-6.

A comparison of fluconazole and itraconazole in the management of denture stomatitis: a pilot study

OBJECTIVES

To compare fluconazole capsules (50 mg daily for 14 days) and itraconazole capsules (100 mg daily for 15 days) in the treatment of denture stomatitis, using objective clinical and mycological outcome measures.

METHODS

Twenty complete denture wearers with denture stomatitis were enrolled. At baseline, palatal erythema was measured with an electro-optical instrument, a denture disc specimen was collected from the fitting surface of the denture for culture and an oral rinse and imprint cultures were collected for mycological culture. Ten patients received fluconazole capsules (50 mg daily for 14 days) and 10 received itraconazole capsules (100 mg daily for 15 days). Palatal erythema was reassessed and the microbiological specimens re-collected on day 14.

RESULTS

The most common form of denture stomatitis seen in this group of patients was Newton's Type II. All patients responded to advice to leave their dentures out at night but there was a poor overall improvement in denture hygiene. There was an objective reduction in palatal erythema following treatment with both fluconazole and itraconazole. A wide range of yeasts were isolated from the mouths of all the denture stomatitis patients before treatment. C. albicans was the most common isolate. A mycological cure was achieved in only five of the 20 patients, one in the fluconazole group and four in the itraconazole group. A further eight patients in the fluconazole group and three in the itraconazole group had reduced yeast counts by the second visit.

CONCLUSION

Fluconazole and itraconazole were of comparable efficacy in the treatment of denture stomatitis, on the basis of reduction in palatal erythema and mycological culture.

A vision-based three-dimensional capture system for maxillofacial assessment and surgical planning

We describe a vision-based three-dimensional facial data capture system designed for the planning of maxillofacial operations. We describe the system requirements and outline the methods used to develop a complete three-dimensional facial capture system. Our approach is based upon imaging the face using two stereo-pair sets of cameras. Scale-space-based stereo-matching is then used to recover correspondences between each of the captured stereo-pairs. Photogrammetric routines based on adjustment of bundles are used off-line to calibrate the system by imaging a single object that references all cameras to the same co-ordinate frame. This calibration scheme allows us to convert stereo correspondences to world points for each pair of cameras without the need for any subsequent fusion of data. Initial results show that we are able to capture key facial landmarks to within 0.5 mm.

Update on oral lichen planus: etiopathogenesis and management

Lichen planus (LP) is a relatively common disorder of the stratified squamous epithelia, which is, in many ways, an enigma. This paper is the consensus outcome of a workshop held in Switzerland in 1995, involving a selection of clinicians and scientists with an interest in the condition and its management. The oral (OLP) eruptions usually have a distinct clinical morphology and characteristic distribution, but OLP may also present a confusing array of patterns and forms, and other disorders may clinically simulate OLP. Lesions may affect other mucosae and/or skin. Lichen planus is probably of multifactorial origin, sometimes induced by drugs or dental materials, often idiopathic, and with an immunopathogenesis involving T-cells in particular. The etiopathogenesis appears to be complex, with interactions between and among genetic, environmental, and lifestyle factors, but much has now been clarified about the mechanisms involved, and interesting new associations, such as with liver disease, have emerged. The management of lichen planus is still not totally satisfactory, and there is as yet no definitive treatment, but there have been advances in the control of the condition. There is no curative treatment available; immunomodulation, however, can control the condition. Based on the observed increased risk of malignant development, OLP patients should be offered regular follow-up examination from two to four times annually and asked to report any changes in their lesions and/or symptoms. Follow-up may be particularly important in patients with atrophic/ulcerative/erosive affections of the tongue, the gingiva, or the buccal mucosa. Much more research is required into the genetic and environmental aspects of lichen planus, into the premalignant potential, and into the possible associations with chronic liver, and other disorders. More clinical studies are required into the possible efficacy of immunomodulatory drugs such as pentoxifylline and thalidomide.

A controlled study of gold contact hypersensitivity

1203 patients attending for routine patch testing at 3 hospitals and 105 volunteers were tested with 0.5% and 0.05% gold sodium thiosulfate (GST). 38 patients (3.2%) and 5 volunteers (4.8%) had positive patch tests to GST. There were no significant differences between volunteers and patients with respect to age, sex, atopy or exposure to gold in dental restorations, jewellery or through occupation. There were no significant differences in prevalence of GST hypersensitivity in the 3 hospitals, or between patients and controls. This is the 1st controlled study of hypersensitivity to GST, and suggests that routine patch testing to gold is of limited clinical benefit.

Three-dimensional modeling for modern diagnosis and planning in maxillofacial surgery

The existing methods of recording the face in three dimensions are reviewed, and a new method for three-dimensional facial modeling is introduced. The technique utilizes two stereo pairs of videocameras, a stereo pair at each side of the patient's face. The system allows rapid capture of the face in three dimensions and precise measurement of anatomic landmarks. The system can be used to capture the facial image and a cephalogram almost simultaneously, allowing more accurate superimposition of soft and hard tissues. This precision will facilitate development of the surgical treatment plan. A computer program in the early stages of development will use the data generated by this biostereometric measurement system to predict soft tissue changes following orthognathic surgery.

A three-dimensional imaging system for archiving dental study casts: a preliminary report

Dental study casts form an essential part of patient records for both diagnostic and medicolegal purposes. Storage of study casts poses major problems because of inconvenience and cost of mass storage. Various methods for recording and storage of study casts are discussed. A new biostereometric technique for digitally recording and storing dental casts, and using the recent advances in stereophotogrammetry, is presented. Archiving dental casts in a digital format would reduce problems of mass storage and provide new benefits such as duplication of casts and use in clinical and research studies.