ABSTRACT
OBJECTIVE: To present our data evaluating the feasibility of simultaneous cochlear implantation with resection of acoustic neuroma. METHODS: This paper describes a case series of eight adult patients with a radiologically suspected acoustic neuroma, treated at a tertiary referral centre in Newcastle, Australia, between 2012 and 2015. Patients underwent cochlear implantation concurrently with removal of an acoustic neuroma. The approach was translabyrinthine, with facial nerve monitoring and electrically evoked auditory brainstem response testing. Standard post-implant rehabilitation was employed, with three and six months' follow-up data collected. The main outcome measures were: hearing, subjective benefit of implant, operative complications and tumour recurrence. RESULTS: Eight patients underwent simultaneous cochlear implantation with resection of acoustic neuroma over a 3-year period, and had 25-63 months' follow up. There were no major complications. All patients except one gained usable hearing and were daily implant users. CONCLUSION: Simultaneous cochlear implantation with resection of acoustic neuroma has been shown to be a safe treatment option, which will be applicable in a wide range of clinical scenarios as the indications for cochlear implantation continue to expand.
Subject(s)
Cochlear Implantation/methods , Combined Modality Therapy/methods , Hearing/physiology , Neuroma, Acoustic/surgery , Adolescent , Aged , Australia/epidemiology , Combined Modality Therapy/statistics & numerical data , Evoked Potentials, Auditory, Brain Stem/physiology , Facial Nerve/surgery , Feasibility Studies , Follow-Up Studies , Hearing Tests/methods , Humans , Middle Aged , Neoplasm Recurrence, Local/epidemiology , Neuroma, Acoustic/diagnostic imaging , Neuroma, Acoustic/pathology , Neuroma, Acoustic/rehabilitation , Postoperative Complications/epidemiology , Retrospective Studies , Tertiary Care Centers , Treatment OutcomeSubject(s)
Basophils/physiology , Mast Cells/physiology , Animals , Humans , Inflammation/etiology , ResearchABSTRACT
We use Brownian dynamics (BD) simulations to study the ionic conduction and valence selectivity of a generic electrostatic model of a biological ion channel as functions of the fixed charge Q(f) at its selectivity filter. We are thus able to reconcile the discrete calcium conduction bands recently revealed in our BD simulations, M0 (Q(f)=1e), M1 (3e), M2 (5e), with a set of sodium conduction bands L0 (0.5e), L1 (1.5e), thereby obtaining a completed pattern of conduction and selectivity bands vs Q(f) for the sodium-calcium channels family. An increase of Q(f) leads to an increase of calcium selectivity: L0 (sodium-selective, nonblocking channel) â M0 (nonselective channel) â L1 (sodium-selective channel with divalent block) â M1 (calcium-selective channel exhibiting the anomalous mole fraction effect). We create a consistent identification scheme where the L0 band is putatively identified with the eukaryotic sodium channel The scheme created is able to account for the experimentally observed mutation-induced transformations between nonselective channels, sodium-selective channels, and calcium-selective channels, which we interpret as transitions between different rows of the identification table. By considering the potential energy changes during permeation, we show explicitly that the multi-ion conduction bands of calcium and sodium channels arise as the result of resonant barrierless conduction. The pattern of periodic conduction bands is explained on the basis of sequential neutralization taking account of self-energy, as Q(f)(z,i)=ze(1/2+i), where i is the order of the band and z is the valence of the ion. Our results confirm the crucial influence of electrostatic interactions on conduction and on the Ca(2+)/Na(+) valence selectivity of calcium and sodium ion channels. The model and results could be also applicable to biomimetic nanopores with charged walls.
Subject(s)
Calcium Channels/genetics , Calcium Channels/metabolism , Models, Biological , Mutation , Sodium Channels/genetics , Sodium Channels/metabolism , Calcium/metabolism , Reproducibility of Results , Sodium/metabolism , Substrate Specificity , ThermodynamicsABSTRACT
We report self-consistent Brownian dynamics simulations of a simple electrostatic model of the selectivity filters (SF) of calcium ion channels. They reveal regular structure in the conductance and selectivity as functions of the fixed negative charge Qf at the SF. With increasing Qf, there are distinct regions of high conductance (conduction bands) M0, M1, M2 separated by regions of almost zero-conductance (stop-bands). Two of these conduction bands, M1 and M2, are related to the saturated calcium occupancies of P = 1 and P = 2, respectively and demonstrate self-sustained conductivity. Despite the model's limitations, its M1 and M2 bands show high calcium selectivity and prominent anomalous mole fraction effects and can be identified with the L-type and RyR calcium channels. The non-selective band M0 can be identified with a non-selective cation channel, or with OmpF porin.
Subject(s)
Calcium Channels/metabolism , Calcium/metabolism , Computer Simulation , Models, Biological , Calcium Channels/chemistry , Electric Conductivity , Static ElectricityABSTRACT
Dental surgeons may encounter in their clinical practice patients who present with aggressive pathologies that require early diagnosis and prompt treatment. This action may limit the extent of tissue damage and, where relevant, improve survival outcome. Clinicians should therefore be aware of the range of resective, reconstructive and rehabilitative options that are available in the management of these patients. We present our experience with the free fibula flap used for oromandibular reconstruction; this was undertaken in 21 patients following resective surgery for malignant pathology, cytologically benign but biologically aggressive odontogenic pathology and radiation induced osteonecrosis. We also review the history, surgical anatomy, surgical assessment and potential complications that are relevant to the free fibula flap.
Subject(s)
Free Tissue Flaps , Jaw Diseases/surgery , Mandible/surgery , Mandibular Reconstruction/methods , Oral Surgical Procedures/methods , Adolescent , Adult , Aged , Carcinoma, Squamous Cell/surgery , Female , Free Tissue Flaps/adverse effects , Humans , Male , Mandible/diagnostic imaging , Mandibular Reconstruction/adverse effects , Middle Aged , Odontogenic Cysts/surgery , Osteoradionecrosis/surgery , RadiographyABSTRACT
Imidocarb [N,N'-bis[3-(4,5-dihydro-1H-imidazol-2-yl)phenyl]urea, C(19)H(20)N(6)O(1), m.w. 348.41] is a symmetrical carbanilide derivative used to treat disease caused by protozoans of the Babesia genus. Imidocarb, however, is also considered capable of suppressing Babesia-specific immune responses, allowing Babesia-positive horses to pass a complement fixation test (CFT) without eliminating the infection. This scenario could enable Babesia-infected horses to pass CFT-based importation tests. It is imperative to unequivocally identify and quantify equine tissue residues of imidocarb by mass spectrometry to address this issue. As a pretext to development of sensitive tissue assays, we have investigated possibilities of mass spectrometric (MS) detection of imidocarb. Our analyses disclosed that an unequivocal mass spectral analysis of imidocarb is challenging because of its rapid fragmentation under standard gas chromatography (GC)-MS conditions. In contrast, solution chemistry of imidocarb is more stable but involves distribution into mono- and dicationic species, m/z 349 and 175, respectively, in acid owing to the compound's inherent symmetrical nature. Dicationic imidocarb was the preferred complex as viewed by either direct infusion-electrospray-MS or by liquid chromatography (LC)-MS. Dicationic imidocarb multiple reaction monitoring (MRM: m/z 175 â 162, 145, and 188) therefore offer the greatest opportunities for sensitive detection and LC-MS is more likely than GC-MS to yield a useful quantitative forensic analytical method for detecting imidocarb in horses.
Subject(s)
Antiprotozoal Agents/chemistry , Imidocarb/chemistry , Mass Spectrometry/methods , Antiprotozoal Agents/analysis , Chromatography, Liquid , Gas Chromatography-Mass Spectrometry , Imidocarb/analysisABSTRACT
UNLABELLED: Intra-and inter-reader reliability of semi-automated quantitative vertebral morphometry measurements was determined using lateral computed tomography (CT) scout views. The method requires less time than conventional morphometry. Reliability was excellent for vertebral height measurements, good for height ratios, and comparable to semi-quantitative grading by radiologists for identification of vertebral fractures. INTRODUCTION: Underdiagnosis and undertreatment of vertebral fracture (VFx) is a well-known problem worldwide. Thus, new methods are needed to facilitate identification of VFx. This study aimed to determine intra- and inter-reader reliability of semi-automated quantitative vertebral morphometry based on shape-based statistical modeling (SpineAnalyzer, Optasia Medical, Cheadle, UK). METHODS: Two non-radiologists independently assessed vertebral morphometry from CT lateral scout views at two time points in 96 subjects (50 men, 46 women, 70.3 ± 8.9 years) selected from the Framingham Heart Study Offspring and Third Generation Multi-Detector CT Study. VFxs were classified based solely on morphometry measurements using Genant's criteria. Intraclass correlation coefficients (ICCs), root mean squared coefficient of variation (RMS CV) and kappa (k) statistics were used to assess reliability. RESULTS: We analyzed 1,246 vertebrae in 96 subjects. The analysis time averaged 5.4 ± 1.7 min per subject (range, 3.2-9.1 min). Intra-and inter-reader ICCs for vertebral heights were excellent (>0.95) for all vertebral levels combined. Intra-and inter-reader RMS CV for height measurements ranged from 2.5% to 3.9% and 3.3% to 4.4%, respectively. Reliability of vertebral height ratios was good to fair. Based on morphometry measurements alone, readers A and B identified 51-52 and 46-59 subjects with at least one prevalent VFx, respectively, and there was a good intra-and inter-reader agreement (k = 0.59-0.69) for VFx identification. CONCLUSIONS: Semi-automated quantitative vertebral morphometry measurements from CT lateral scout views are convenient and reproducible, and may facilitate assessment of VFx.
Subject(s)
Lumbar Vertebrae/diagnostic imaging , Spinal Fractures/diagnostic imaging , Thoracic Vertebrae/diagnostic imaging , Tomography, X-Ray Computed/statistics & numerical data , Aged , Aged, 80 and over , Algorithms , Female , Humans , Lumbar Vertebrae/anatomy & histology , Male , Middle Aged , Observer Variation , Reproducibility of Results , Thoracic Vertebrae/anatomy & histologyABSTRACT
A self-consistent analytic approach is introduced for the estimation of the access resistance and the current through an open ion channel for an arbitrary number of species. For an ion current flowing radially inward from infinity to the channel mouth, the Poisson-Boltzmann-Nernst-Planck equations are solved analytically in the bulk with spherical symmetry in three dimensions, by linearization. Within the channel, the Poisson-Nernst-Planck equation is solved analytically in a one-dimensional approximation. An iterative procedure is used to match the two solutions together at the channel mouth in a self-consistent way. It is shown that the current-voltage characteristics obtained are in good quantitative agreement with experimental measurements.
Subject(s)
Electric Conductivity , Ion Channel Gating , Ion Channels/metabolism , Models, Biological , Diffusion , Ion Channels/chemistry , Linear Models , Porosity , Static ElectricityABSTRACT
OBJECTIVE: To study the effects in systemic lupus erythaematosus (SLE) of B cell directed therapy with rituximab, a chimeric monoclonal antibody directed at CD20+ B cells, without concomitant immunosuppressive therapy in mild to moderate SLE. METHODS: Patients (n=24) with active SLE and failure of >or=1 immunosuppressive were recruited from three university centres into this phase I/II prospective open-label study. Patients were followed for 1 year to assess safety, efficacy and biological effects. RESULTS: In total, 18 of the patients scheduled to receive the full lymphoma dose of rituximab were evaluable for B cell levels in peripheral blood. Of these, 17 had effective CD19+ B cell depletion (<5 cells/microl). However, six of the depleted patients showed B cell return before 24 weeks. A total of 70% of patients improved by week 55, as defined by an SLE Disease Activity Index (SLEDAI) score improvement of >or=2 units from baseline. The degree of CD19+ B cell depletion was correlated with SLEDAI improvement at week 15 (r=0.84). In general, rituximab infusions were well tolerated. Approximately a third of the patients developed human anti-chimeric antibody (HACA) titres, which correlated with poor B cell depletion. Most patients (9 of 14) did not respond to immunisations with Pneumovax and tetanus toxoid. CONCLUSIONS: Rituximab is a promising new therapy for SLE. The variability of responses in patients with SLE may be related to HACA formation. The failure to respond to immunisations is surprising, in view of the apparently low risk of infections. Better biological markers are necessary to follow these patients during treatment.
Subject(s)
Antibodies, Monoclonal/therapeutic use , Immunosuppressive Agents/therapeutic use , Lupus Erythematosus, Systemic/drug therapy , Adult , Antibodies, Monoclonal/adverse effects , Antibodies, Monoclonal, Murine-Derived , Antigens, CD20/immunology , B-Lymphocytes/drug effects , Female , Humans , Immunosuppressive Agents/adverse effects , Lupus Erythematosus, Systemic/immunology , Lymphocyte Count , Lymphocyte Depletion/methods , Male , Middle Aged , Prospective Studies , Rituximab , Treatment Outcome , Young AdultABSTRACT
Ion channels are proteins with a narrow hole down their middle that control a wide range of biological function by controlling the flow of spherical ions from one macroscopic region to another. Ion channels do not change their conformation on the biological time scale once they are open, so they can be described by a combination of Poisson and drift-diffusion (Nernst-Planck) equations called PNP in biophysics. We use singular perturbation techniques to analyse the steady-state PNP system for a channel with a general geometry and a piecewise constant permanent charge profile. We construct an outer solution for the case of a constant permanent charge density in three dimensions that is also a valid solution of the one-dimensional system. The asymptotical current-voltage (I-V ) characteristic curve of the device (obtained by the singular perturbation analysis) is shown to be a very good approximation of the numerical I-V curve (obtained by solving the system numerically). The physical constraint of non-negative concentrations implies a unique solution, i.e., for each given applied potential there corresponds a unique electric current (relaxing this constraint yields non-physical multiple solutions for sufficiently large voltages).
ABSTRACT
We demonstrate the microfabrication of a low-noise silicon based device with integrated silver/silver chloride electrodes used for the measurement of single ion channel proteins. An aperture of 150 microm diameter was etched in a silicon substrate using a deep silicon reactive ion etcher and passivated with 30 nm of polytetrafluoroethylene via chemical vapor deposition. The average recorded noise in measurements of lipid bilayers was reduced by a factor of four through patterning of a 75 microm thick SU-8 layer around the aperture. Integrated electrodes were fabricated on both sides of the device and used for repeatable, stable, giga-seal bilayer formations as well as characteristic measurements of the transmembrane protein OmpF porin.
Subject(s)
Biosensing Techniques/instrumentation , Electrochemistry/instrumentation , Ion Channels/chemistry , Lipid Bilayers/chemistry , Microelectrodes , Porins/chemistry , Silicon/chemistry , Biomimetics/instrumentation , Biomimetics/methods , Biosensing Techniques/methods , Electrochemistry/methods , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity , Systems IntegrationSubject(s)
Antibodies, Monoclonal/therapeutic use , Antirheumatic Agents/therapeutic use , Arthritis, Rheumatoid/drug therapy , Autoimmune Diseases/drug therapy , Antibodies, Monoclonal, Murine-Derived , Humans , Randomized Controlled Trials as Topic , Rituximab , Tumor Necrosis Factor-alpha/antagonists & inhibitorsABSTRACT
The access resistance (AR) of a channel is an important component of the conductance of ion channels, particularly in wide and short channels, where it accounts for a substantial fraction of the total resistance to the movement of ions. The AR is usually calculated by using a classical and simple expression derived by Hall from electrostatics (J.E. Hall 1975 J. Gen. Phys. 66:531-532), though other expressions, both analytical and numerical, have been proposed. Here we report some numerical results for the AR of a channel obtained by solving the Poisson-Nernst-Planck equations at the entrance of a circular pore. Agreement is found between numerical calculations and analytical results from Hall's equation for uncharged pores in neutral membranes. However, for channels embedded in charged membranes, Hall's expression overestimates the AR, which is much lower and can even be neglected in some cases. The weak dependence of AR on the pore radius for charged membranes at low salt concentration can be exploited to separate the channel and the access contributions to the measured conductance.
Subject(s)
Computational Biology/methods , Biological Transport , Biophysics/methods , Cell Membrane/metabolism , Computer Simulation , Diffusion , Electric Conductivity , Electric Impedance , Ion Transport , Ions , Kinetics , Models, Biological , Models, Molecular , Models, Statistical , Poisson Distribution , Salts/pharmacology , Sodium Chloride/pharmacology , Static ElectricityABSTRACT
The ionic current flowing through a protein channel in the membrane of a biological cell depends on the concentration of the permeant ion, as well as on many other variables. As the concentration increases, the rate of arrival of bath ions to the channel's entrance increases, and typically so does the net current. This concentration dependence is part of traditional diffusion and rate models that predict Michaelis-Menten current-concentration relations for a single ion channel. Such models, however, neglect other effects of bath concentrations on the net current. The net current depends not only on the entrance rate of ions into the channel, but also on forces acting on ions inside the channel. These forces, in turn, depend not only on the applied potential and charge distribution of the channel, but also on the long-range Coulombic interactions with the surrounding bath ions. In this paper, we study the effects of bath concentrations on the average force on an ion in a single ion channel. We show that the force of the reaction field on a discrete ion inside a channel embedded in an uncharged lipid membrane contains a blocking (shielding) term that is proportional to the square root of the ionic bath concentration. We then show that different blocking strengths yield different behavior of the current-concentration and conductance-concentration curves. Our theory shows that at low concentrations, when the blocking force is weak, conductance grows linearly with concentration, as in traditional models, e.g., Michaelis-Menten formulations. As the concentration increases to a range of moderate shielding, conductance grows as the square root of concentration, whereas at high concentrations, with high shielding, conductance may actually decrease with increasing concentrations: the conductance-concentration curve can invert. Therefore, electrostatic interactions between bath ions and the single ion inside the channel can explain the different regimes of conductance-concentration relations observed in experiments.
Subject(s)
Cell Membrane/chemistry , Cell Membrane/physiology , Ion Channel Gating/physiology , Ion Channels/chemistry , Ion Channels/physiology , Models, Biological , Models, Chemical , Animals , Computer Simulation , Humans , Membrane Potentials/physiologyABSTRACT
Flux between regions of different concentration occurs in nearly every device involving diffusion, whether an electrochemical cell, a bipolar transistor, or a protein channel in a biological membrane. Diffusion theory has calculated that flux since the time of Fick (1855), and the flux has been known to arise from the stochastic behavior of Brownian trajectories since the time of Einstein (1905), yet the mathematical description of the behavior of trajectories corresponding to different types of boundaries is not complete. We consider the trajectories of noninteracting particles diffusing in a finite region connecting two baths of fixed concentrations. Inside the region, the trajectories of diffusing particles are governed by the Langevin equation. To maintain average concentrations at the boundaries of the region at their values in the baths, a control mechanism is needed to set the boundary dynamics of the trajectories. Different control mechanisms are used in Langevin and Brownian simulations of such systems. We analyze models of controllers and derive equations for the time evolution and spatial distribution of particles inside the domain. Our analysis shows a distinct difference between the time evolution and the steady state concentrations. While the time evolution of the density is governed by an integral operator, the spatial distribution is governed by the familiar Fokker-Planck operator. The boundary conditions for the time dependent density depend on the model of the controller; however, this dependence disappears in the steady state, if the controller is of a renewal type. Renewal-type controllers, however, produce spurious boundary layers that can be catastrophic in simulations of charged particles, because even a tiny net charge can have global effects. The design of a nonrenewal controller that maintains concentrations of noninteracting particles without creating spurious boundary layers at the interface requires the solution of the time-dependent Fokker-Planck equation with absorption of outgoing trajectories and a source of ingoing trajectories on the boundary (the so called albedo problem).
Subject(s)
Cell Membrane/chemistry , Cell Membrane/physiology , Ion Channels/chemistry , Ion Channels/physiology , Models, Biological , Models, Chemical , Biological Transport/physiology , Computer Simulation , Diffusion , Models, Statistical , Particle SizeABSTRACT
In an electrostatic problem with nonuniform geometry, a charge Q in one region induces surface charges [called dielectric boundary charges (DBC)] at boundaries between different dielectrics. These induced surface charges, in return, exert a force [called dielectric boundary force (DBF)] on the charge Q that induced them. The DBF is often overlooked. It is not present in standard continuum theories of (point) ions in or near membranes and proteins, such as Gouy-Chapman, Debye-Huckel, Poisson-Boltzmann or Poisson-Nernst- Planck. The DBF is important when a charge Q is near dielectric interfaces, for example, when ions permeate through protein channels embedded in biological membranes. In this paper, we define the DBF and calculate it explicitly for a planar dielectric wall and for a tunnel geometry resembling the ionic channel gramicidin. In general, we formulate the DBF in a form useful for continuum theories, namely, as a solution of a partial differential equation with boundary conditions. The DBF plays a crucial role in the permeation of ions through the gramicidin channel. A positive ion in the channel produces a DBF of opposite sign to that of the fixed charge force (FCF) produced by the permanent charge of the gramicidin polypeptide, and so the net force on the positive ion is reduced. A negative ion creates a DBF of the same sign as the FCF and so the net (repulsive) force on the negative ion is increased. Thus, a positive ion can permeate the channel, while a negative ion is excluded from it. In gramicidin, it is this balance between the FCF and DBF that allows only singly charged positive ions to move into and through the channel. The DBF is not directly responsible, however, for selectivity between the alkali metal ions (e.g., Li+, Na+, K+): we prove that the DBF on a mobile spherical ion is independent of the ion's radius.
Subject(s)
Gramicidin/chemistry , Biophysical Phenomena , Biophysics , Calcium/chemistry , Ions , Models, ChemicalABSTRACT
The rapid spread of herpes simplex virus type 1 (HSV-1) in mucosal epithelia and neuronal tissue depends primarily on the ability of the virus to navigate within polarized cells and the tissues they constitute. To understand HSV entry and the spread of virus across cell junctions, we have previously characterized a human keratinocyte cell line, HaCaT. These cells appear to reflect cells infected in vivo more accurately than many of the cultured cells used to propagate HSV. HSV mutants lacking gE/gI are highly compromised in spread within epithelial and neuronal tissues and also show defects in cell-to-cell spread in HaCaT cells, but not in other, nonpolarized cells. HSV gD is normally considered absolutely essential for entry and cell-to-cell spread, both in cultured cells and in vivo. Here, an HSV-1 gD mutant virus, F-US6kan, was found to efficiently enter HaCaT cells and normal human keratinocytes and could spread from cell to cell without gD provided by complementing cells. By contrast, entry and spread into other cells, especially highly transformed cells commonly used to propagate HSV, were extremely inefficient. Further analyses of F-US6kan indicated that this mutant expressed extraordinarily low (1/500 wild-type) levels of gD. Neutralizing anti-gD monoclonal antibodies inhibited entry of F-US6kan, suggesting F-US6kan utilized this small amount of gD to enter cells. HaCaT cells expressed high levels of an HSV gD receptor, HveC, and entry of F-US6kan into HaCaT cells could also be inhibited with antibodies specific for HveC. Interestingly, anti-HveC antibodies were not fully able to inhibit entry of wild-type HSV-1 into HaCaT cells. These results help to uncover important properties of HSV and human keratinocytes. HSV, with exceedingly low levels of a crucial receptor-binding glycoprotein, can enter cells expressing high levels of receptor. In this case, surplus gD may be useful to avoid neutralization by anti-gD antibodies.