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PubMed2003

Structural-functional characterization of the cathodic haemoglobin of the conger eel Conger conger: molecular modelling study of an additional phosphate-binding site.

The protein sequence data for the alpha- and beta-chains have been deposited in the SWISS-PROT and TrEMBL protein knowledgebase under the accession numbers P83479 and P83478 respectively. The Conger conger (conger eel) haemoglobin (Hb) system is made of three components, one of which, the so-called cathodic Hb, representing approx. 20% of the total pigment, has been purified and characterized from both a structural and functional point of view. Stripped Hb showed a reverse Bohr effect, high oxygen affinity and slightly low cooperativity in the absence of any effector. Addition of saturating GTP strongly influences the pH dependence of the oxygen affinity, since the reverse Bohr effect, observed under stripped conditions, is converted into a small normal Bohr effect. A further investigation of the GTP effect on oxygen affinity, carried out by fitting its titration curve, demonstrated the presence of two independent binding sites. Therefore, on the basis of the amino acid sequence of the alpha- and beta-chains, which have been determined, a computer modelling study has been performed. The data suggest that C. conger cathodic Hb may bind organic phosphates at two distinct binding sites located along the central cavity of the tetramer by hydrogen bonds and/or electrostatic interactions with amino acid residues of both chains, which have been identified. Among these residues, the two Lys-alpha(G6) (where the letter refers to the haemoglobin helix and the number to the amino acid position in the helix) appear to have a key role in the GTP movement from the external binding region to the internal central cavity of the tetrameric molecule.

Allosteric Regulation↗
PubMed1997

Human corneal epithelial cells reorient and migrate cathodally in a small applied electric field.

PURPOSE: To test whether human corneal epithelial cells (HCECs) respond to small applied electric fields (EFs) in a similar manner to bovine corneal epithelial cells (BCECs), the orientation and directed migration in small EFs of both primary cultures and of a human corneal epithelial cell line were quantified. METHODS: Primary cultures of human corneal epithelial cells (PHCECs) and transformed human corneal epithelial cells (THCECs) were exposed to EFs (100 mV/mm-250 mV/mm) in different media. Cell migration was traced using an image analyser. RESULTS: PHCECs and THCECs reoriented and migrated towards the cathode (negative pole) when cultured in small direct current (dc) EFs. Both the reorientation and directional migration were voltage- and serum-dependent, as shown previously for bovine cells. PHCECs and THCECs showed significant perpendicular orientation in EFs at 150 mV/mm in medium with serum, while at the same voltage, no significant orientation was found in serum free medium. PHCECs started to show perpendicular reorientation around 30 min after onset of EF at 150 mV/mm. They showed significant directional migration at 150 mV/mm, with directedness of 0.35 +/- 0.07 and a migration rate of 9.1 +/- 0.7 microns/h (n = 90), both significantly higher than that of cells in serum free medium. Addition of EGF-induced significant reorientation and directional migration of THCECs at 100 mV/mm. Additionally, as for BCECs, which remained viable and responsive to electric fields for at least 75 h at 150 mV/mm, THCECs also remained viable and showed responsiveness during long periods of exposure to EFs (at least 20 h). CONCLUSIONS: Cultured human primary CECs and a human corneal epithelial cell line both responded to small EFs with perpendicular reorientation and cathodally-directed migration. Cell responses were qualitatively similar to those reported previously for bovine CECs. The endogenous EFs generated by wounded cornea may play an important role in promoting cell shape changes and directed migration of CECs during the healing process.

Animals↗
PubMed2005

Fabrication of nanoelectrodes for neurophysiology: cathodic electrophoretic paint insulation and focused ion beam milling.

The fabrication and characterization of tungsten nanoelectrodes insulated with cathodic electrophoretic paint is described together with their application within the field of neurophysiology. The tip of a 127 mum diameter tungsten wire was etched down to less than 100 nm and then insulated with cathodic electrophoretic paint. Focused ion beam (FIB) polishing was employed to remove the insulation at the electrode's apex, leaving a nanoscale sized conductive tip of 100-1000 nm. The nanoelectrodes were examined by scanning electron microscopy (SEM) and their electrochemical properties characterized by steady state linear sweep voltammetry. Electrode impedance at 1 kHz was measured too. The ability of a 700 nm tipped electrode to record well-isolated action potentials extracellularly from single visual neurons in vivo was demonstrated. Such electrodes have the potential to open new populations of neurons to study.

Journal Article↗
PubMed1997

Effect of anode-cathode configuration on paresthesia coverage in spinal cord stimulation.

OBJECTIVE: To provide a theoretical basis for the selection of the anode-cathode configuration in spinal cord stimulation for the management pain when one percutaneous epidural electrode or two electrodes in parallel are used. METHODS: A computer model of spinal cord stimulation at T8-T9 was used to calculate the dorsal column areas recruited in stimulation by various configurations used in clinical practice. RESULTS: Tripolar (or bipolar) stimulation by a single electrode, symmetrically placed over the dorsal columns, recruits the largest area and will give the widest paresthesia coverage. Stimulation by two symmetrically placed electrodes connected in parallel to a single channel pulse generator may give similar results, because of their generally smaller distance from the spinal cord, but a "summation effect" does not exist. A smaller dorsal column area is activated when two offset electrodes are used. An electrode placed laterally or transverse bipolar stimulation results in unilateral, usually segmentary, paresthesia. CONCLUSIONS: The relative positions of cathodes and anodes and their distance from the spinal cord are the major determinants of dorsal column/dorsal root activation and paresthesia distribution. The large interpatient variability of the intraspinal geometry is the main cause of differences in paresthesia coverage among patients having optimally placed electrode(s). Changes of paresthesia coverage over time are more probable when multiple electrodes are used.

Computer Simulation↗
PubMed1992

Influence of polarographic cathode diameter on measured oxygen transmissibility of hydrogel contact lenses with optical power.

The oxygen transmissibility of a contact lens is defined as its oxygen permeability (Dk) divided by its thickness (L). Transmissibility can be obtained from separate measurements of Dk and L, or from a single measurement of oxygen flux through the lens (as for example by the polarographic method). Dk/L of hydrogel contact lenses with optical power measured by the polarographic method was compared with Dk/L calculated from separate measurements of Dk and L. Polarographic sensors of different cathode diameters were used to show the effect of the area over which the flux is measured on the observed Dk/L. Dk/L from oxygen flux measured by the polarographic sensor was found to be a function of the optical power of the lens and cathode diameter. Dk/L calculated from separately determined Dk and L for optically powered lenses was found to be a function of Dk and the choice of L (central or average).

Contact Lenses↗
PubMed2000

Nitrogen atom energy distributions in a hollow-cathode planar sputtering magnetron

Energy distributions of nitrogen atoms (N) in a hollow-cathode planar sputtering magnetron were obtained by use of optical emission spectroscopy. A characteristic line, N I 8216.3 A, well separated from molecular nitrogen emission bands, was identified. Jansson's nonlinear spectral deconvolution method, refined by minimization of chi(2)(w), was used to obtain the optimal deconvolved spectra. These showed nitrogen atom energies from 1 eV to beyond 500 eV. Based on comparisons with VFTRIM computer code results, it is proposed that the energetic N's are generated from N+2 ions after these ions are accelerated through the sheath and dissociatively reflect from the cathode.

Journal Article↗
PubMed2005

Development of a cathode-directed streamer discharge in air at different pressures: experiment and comparison with direct numerical simulation.

The results are given of an experimental investigation of a cathode-directed streamer discharge in synthetic air in the pressure range from 760 to 300 torr and their comparison with the results of direct numerical simulation in a 2D hydrodynamic approximation. The pattern of discharge branching upon variation of pressure is investigated experimentally. The results are given of comparison of the predicted and measured values of anode current, streamer propagation velocity, and channel diameter. It has been demonstrated that the electric field in the streamer head is hardly affected by the pressure decrease, while the electron concentration decreases with pressure by an order of magnitude. At the same time, production of chemical species in a cathode-directed streamer discharge varies at a rate of at least the second power of inverse pressure.

Journal Article↗
PubMed2005

Influence of electron recapture by the cathode upon the discharge characteristics in dc planar magnetrons.

In dc magnetrons the electrons emitted from the cathode may return there due to the applied magnetic field. When that happens, they can be recaptured or reflected back into the discharge, depending on the value of the reflection coefficient (RC). A 2d3v (two-dimensional in coordinate and three-dimensional in velocity space) particle-in-cell-Monte Carlo model, including an external circuit, is developed to determine the role of the electron recapture in the discharge processes. The detailed discharge structure as a function of RC for two pressures (4 and 25 mtorr) is studied. The importance of electron recapture is clearly manifested, especially at low pressures. The results indicate that the discharge characteristics are dramatically changed with varying RC between 0 and 1. Thus, the electron recapture at the cathode appears to be a significant mechanism in magnetron discharges and RC a very important parameter in their correct quantitative description that should be dealt with cautiously.

Journal Article↗
PubMed2004

X-ray absorption spectroscopy study of the LixFePO4 cathode during cycling using a novel electrochemical in situ reaction cell.

The extraction and insertion of lithium in LiFePO4 has been investigated in practical Li-ion intercalation electrodes for Li-ion batteries using Fe K-edge X-ray absorption spectroscopy (XAS). A versatile electrochemical in situ reaction cell was utilized, specifically designed for long-term X-ray experiments on battery electrodes during the lithium-extraction/insertion process in electrode materials for Li-ion batteries. The electrode contained about 7.7 mg of LiFePO4 on a 20 microm-thick Al foil. In order to determine the charge compensation mechanism and structural perturbations occurring in the system during cycling, in situ X-ray absorption fine-structure spectroscopy (XAFS) measurements were conducted on the cell at a moderate rate using typical Li-ion battery operating voltages (3.0-4.1 V versus Li/Li+). XAS studies of the LiFePO4 electrode measured at the initial state (LiFePO4) showed iron to be in the Fe(II) state corresponding to the initial state (0.0 mAh) of the battery, whereas in the delithiated state (FePO4) iron was found to be in the Fe(III) state corresponding to the final charged state (3 mAh) of the battery. The X-ray absorption near-edge structure (XANES) region of the XAS spectra revealed a high-spin configuration for the two states [Fe(II), d6 and Fe(III), d5]. The XAFS data analysis confirmed that the olivine structure of the LiFePO4 and FePO4 is retained by the electrodes, which is in agreement with the X-ray diffraction observations on these compounds. The XAFS data that were collected continuously during cycling revealed details about the response of the cathode to Li insertion and extraction. These measurements on the LiFePO4 cathode show that the material retains good structural short-range order leading to superior cycling.

Electric Power Supplies↗
PubMed1994

Selective stimulation of smaller fibers in a compound nerve trunk with single cathode by rectangular current pulses.

Electrical stimulation of unmyelinated nerve fibers is analyzed, using point sources in a simple volume conductor model and a dynamic Hodgkin-Huxley model of nerve fiber. The excitation and blocking threshold of single cathode stimulation with an indifference anode at infinity are calculated by solving difference equations with axons of different diameters. The relation between the blocking threshold and the pulsewidth of single cathode stimulation is also calculated. The results suggest a method of selectively stimulating the smaller fibers in a compound nerve trunk. Two kinds of stimulation electrodes are designed to test this method. Both of them are proven to yield results in accordance with our model by the animal experiments on a toad's sciatic nerve trunk. It is possible to excite the smaller fibers without exciting the larger ones in a compound nerve trunk by properly controlling the stimulus intensity. The method is likely to be used in both physiological experiments and neural prostheses.

Action Potentials↗
PubMed1982

Serum concentration of cathodic trypsin-like immunoreactivity and pancreatic isoamylase in insulin-dependent diabetes mellitus.

The relationship between diabetes mellitus and the exocrine pancreatic function was evaluated in 29 patients with insulin-dependent diabetes mellitus by measuring cathodic trypsin-like immunoreactivity (TLI) and the enzymatic activity of pancreatic isoamylase in serum before and 90 min after breakfast and insulin. Thirty healthy subjects served as reference group. Median fasting serum concentrations in the diabetic subjects were significantly lower than in the reference subjects: for TLI 143 and 299 micrograms trypsin standard/l and for pancreatic isoamylase 43 and 101 U/l, respectively (p less than 0.001 for both). A positive correlation between TLI and pancreatic isoamylase was present in the diabetics (Sperman's rho = 0.56, p less than 0.01). The serum concentrations of TLI and pancreatic isoamylase were not related to the duration of diabetes, daily insulin dose or glycemic control measured by blood glucose and total glycosylated hemoglobins. Cathodic TLI and pancreatic isoamylase in serum were not influenced by food and insulin.

Adult↗
PubMed2006

A controlled clinical trial of cathodal DC polarization in patients with refractory epilepsy.

PURPOSE: To study the effects of cathodal DC polarization in patients with refractory epilepsy and malformations of cortical development (MCDs) as indexed by seizure frequency and epileptiform EEG discharges. METHODS: Nineteen patients with MCDs and refractory epilepsy underwent one session of DC polarization (20 min, 1 mA) targeting the epileptogenic focus. The number of epileptiform discharges (EDs) in the EEG and seizures were measured before (baseline), immediately after, and 15 and 30 days after either sham or active DC polarization. Seizure frequency after the treatment was compared with baseline. RESULTS: Active compared with sham DC polarization was associated with a significant reduction in the number of epileptiform discharges [mean ED reduction of -64.3% (95% CI, -122.5% to -6.0%) for the active treatment group and -5.8% (95% CI, -26.8% to 15.2%) for the sham treatment group]. A trend (p = 0.06) was noted for decrease in seizure frequency after active compared with sham treatment [mean seizure frequency decrease of -44.0% (95% CI, -95.0% to 7.1%) for the active treatment group and -11.1% (95% CI, -22.2% to 44.4%) for the sham treatment group]. CONCLUSIONS: This randomized, controlled study shows that cathodal DC polarization does not induce seizures and is well tolerated in patients with refractory epilepsy and MCDs. Furthermore, the results suggest that this technique might have an antiepileptic effect based on clinical and electrophysiological criteria.

Adult↗
PubMedDate not supplied

The development of high-efficiency cathode converters for a multiwire proportional chamber positron camera.

A high-efficiency cathode converter for 511-keV photons has been developed for incorporation into a multiwire proportional chamber (MWPC) positron camera. The converter consists of a honeycomb pattern produced in a 1-mm-thick lead sheet to leave lead walls with a thickness of approximately 60 micron. The converter also serves as the cathode of an MWPC, the gap between the converter and the anode wire plane being 2.5 mm. This small gap results in a high secondary electron extraction efficiency without the need for additional drift voltages. Measurements of the efficiencies of a plane converter and of two types of structured converters in a single section MWPC are described and the efficiency is found to increase in proportion to the converter surface area. This result justifies the use of a simple theoretical model whereby an extrapolation to the efficiency of a detector consisting of a stack of 20 MWPC sections, each section having two converters, is made. The efficiency of this proposed system is calculated to be 17% for 511-keV photons.

Beta Particles↗
PubMed2000

Effects of anodal vs. cathodal pacing on the mechanical performance of the isolated rabbit heart.

Previous studies have suggested that anodal pacing enhances electrical conduction in the heart near the pacing site. It was hypothesized that enhanced conduction by anodal pacing would also enhance ventricular pressure in the heart. Left ventricular pressure measurements were made in isolated, Langendorff-perfused rabbit hearts by means of a Millar pressure transducer with the use of a balloon catheter fixed in the left ventricle. The pressure wave was analyzed for maximum pressure (Pmax) generated in the left ventricle and the work done by the left ventricle (Parea). Eight hearts were paced with monophasic square-wave pulses of varying amplitudes (2, 4, 6, and 8 V) with 100 pulses of each waveform delivered to the epicardium. Anodal stimulation pulses showed statistically significant improvement in mechanical response at 2, 4, and 8 V. Relative to unipolar cathodal pacing, unipolar anodal pacing improved Pmax by 4.4 +/- 2.3 (SD), 5.3 +/- 3.1, 3.5 +/- 4.9, and 4.8 +/- 1.9% at 2, 4, 6, and 8 V, respectively. Unipolar anodal stimulation also improved Parea by 9.0 +/- 3.0, 12.0 +/- 6.0, 10.1 +/- 7.7, and 11.9 +/- 6.0% at 2, 4, 6, and 8 V, respectively. Improvements in Pmax and Parea indicate that an anodally paced heart has a stronger mechanical response than does a cathodally paced heart. Anodal pacing might be useful as a novel therapeutic technology to treat mechanically impaired or failed hearts.

Animals↗
PubMed1981

Evaluation of the anode and cathode for transcatheter electrocoagulation.

The effect of changing the size and position of the anode and cathode during direct current Transcatheter Electrocoagulation (TCEC) was evaluated in dogs. The results showed that there was no difference in the time required for vessel occlusion when the size and position of the electrodes were changed. However, there were differences noted in the amount of voltage needed to maintain the constant current. Based on these results, for TCEC we recommend positioning the largest possible guidewire anode against the vessel wall. The cathode should be a highly lubricated sponge covered Bovie ground plate.

Animals↗
PubMed1982

Alpha 1-antitrypsin phenotype: transient cathodal shift in serum of infant girl with urinary cytomegalovirus and fatty liver.

A 2-month-old white girl had severe liver disease (but without signs of hepatic necrosis, infection or cirrhosis), urinary cytomegalovirus, transient reduction of alpha 1-antitrypsin concentration and transient abnormal alpha 1-antitrypsin phenotype that were not present in her parents. Five serum specimens that were obtained during the 11/2 months of acute phase liver disease indicated, by polyacrylamide gel isoelectric focusing (PAG-IEF), acid starch gel and agarose electrophoresis as well as immunofixation, an unusual alpha 1-antitrypsin phenotype that we labeled delta (delta). It migrated adjacent to Z, i.e., cathodal of Z and Zpratt on PAG-IEF; anodal of Z but cathodal of X, S, Zpratt on starch gel. We labeled the girl's complete phenotype M delta. After clinical recovery, her phenotype was MM and identical to that of her parents. Hepatic electronmicroscopy of the acute phase specimen showed dilated bile canaliculi. We observed the following in hepatocytes: clusters of globular inclusions surrounded by myelin sheets that, to a lesser extent, also appeared in the liver of CMV-infected children with phenotype MM; dilated endoplasmic reticulum cisternae that contained floccular material; and marked steatosis. These changes were less severe in the convalescent liver specimen.

Cytomegalovirus↗
PubMed1998

Hydrogen ion titrations of the anodic and cathodic haemoglobin components of the European eel Anguilla anguilla.

H+ titrations were conducted on the separated haemoglobin components of eel Anguilla anguilla in both the oxygenated and deoxygenated states. In anodic haemoglobin, the addition of GTP, and to a lesser extent C1-, increased the magnitude of the Haldane effect and shifted its maximum value into the in vivo pH range. Of the 22 histidine residues in the anodic component, only approximately seven were titratable, presumably the beta-chain residues at positions 41, 97, 109 and 146 (helical positions C7, FG4, G11 and HC3, respectively). In cathodic haemoglobin, a small negative Haldane effect was observed at pH values between 6.8 and 8.5 which disappeared in the presence of GTP (molar ratio 3:1 GTP:haemoglobin tetramer). GTP had virtually no effect on the buffer value at fixed oxygenation status, and the lowest buffer value was observed at in vivo pH values. No titratable histidine residues were observed in the cathodic component, indicating that all 14 histidines in this component are buried. We conclude that the anodic component, which constitutes two-thirds of the haemoglobin in the eel, plays the predominant role in CO2 transport and pH homeostasis in vivo.

Anguilla↗
PubMed2004

Spectral matching factors between Super S25 and New S25 photo cathodes and reflective radiation of objects.

According to the response of photoelectric device to a light source, the formula of spectral matching factor of photo cathode-object combination is deduced. The spectral matching factors of Super S25 and New S25 photo cathodes for green vegetation and rough concrete are calculated and compared. For Super S251, the spectral-matching factors for green vegetation and rough concrete are 0.707 and 0.743, respectively, under the full-moon radiation and are 0.504 and 0.577, respectively, under the clear-star radiation. For Super S252, the full-moon factors are 0.561 (green vegetation) and 0.732 (rough concrete), and those for clear-star radiation are 0.338 (green vegetation) and 0.471 (rough concrete). For New S25, the full-moon factors are 0.741 (green vegetation) and 0.762 (rough concrete), and those for clear-star radiation are 0.603 (green vegetation) and 0.657 (rough concrete). An analysis of results shows that the spectral-matching factor has influence on the performance of a low-light level night vision system and is essential for evaluating the visual range of a night-vision system.

Journal Article↗