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PubMed2004

Electrical conductivity imaging using gradient B, decomposition algorithm in magnetic resonance electrical impedance tomography (MREIT).

In magnetic resonance electrical impedance tomography (MREIT), we try to visualize cross-sectional conductivity (or resistivity) images of a subject. We inject electrical currents into the subject through surface electrodes and measure the z component Bz of the induced internal magnetic flux density using an MRI scanner. Here, z is the direction of the main magnetic field of the MRI scanner. We formulate the conductivity image reconstruction problem in MREIT from a careful analysis of the relationship between the injection current and the induced magnetic flux density Bz. Based on the novel mathematical formulation, we propose the gradient Bz decomposition algorithm to reconstruct conductivity images. This new algorithm needs to differentiate Bz only once in contrast to the previously developed harmonic Bz algorithm where the numerical computation of (inverted delta)2Bz is required. The new algorithm, therefore, has the important advantage of much improved noise tolerance. Numerical simulations with added random noise of realistic amounts show the feasibility of the algorithm in practical applications and also its robustness against measurement noise.

Algorithms↗
PubMed2000

Molecular systematics of the African electric fishes (Mormyroidea: teleostei) and a model for the evolution of their electric organs.

We present a new molecular phylogeny for 41 species of African mormyroid electric fishes derived from the 12S, 16S and cytochrome b genes and the nuclear RAG2 gene. From this, we reconstruct the evolution of the complex electric organs of these fishes. Phylogenetic results are generally concordant with earlier preliminary molecular studies of a smaller group of species and with the osteology-based classification of Taverne, which divides the group into the Gymnarchidae and the Mormyridae, with the latter including the subfamilies Petrocephalinae (Petrocephalus) and Mormyrinae (all remaining taxa). However, we find that several genera previously recognized by Taverne are non-monophyletic. Within the Mormyrinae, the genus Myomyrus is the sister group to all the remaining taxa. Other well-supported clades within this group are recovered. A reconstruction of electrocyte evolution on the basis of our best-supported topology suggests that electrocytes with penetrating stalks evolved once early in the history of the mormyrids followed by multiple paedomorphic reversals to electrocytes with non-penetrating stalks.

Animals↗
PubMed2000

[Dampness in an electric plug as a cause of electricity failure in an operation theatre].

Two cases of electricity failure in an operation theatre during open heart surgery are discussed. The fuse for the patient monitor, ventilator, surgery instruments and heart lung machine was blown. Short-circuit was established because of humidity in the plug of the heater for fluid and blood. We recommend sealed or founded plugs and that anaesthesia equipment should not be used as an electrical supply for other electronic apparatus.

Aged↗
PubMed1975

[Electrical stimulation therapy and its effects on the general activity of motor impaired cerebral palsied children; a comparative study of the Bobath physiotherapy and its combination with the Hufschmidt electrical stimulation therapy (author's transl)].

The purpose of this study was to answer the following questions: (1) Is it more effective to treat spastic cerebral palsy with the Hufschmidt electrical stimulation therapy combined with the Bobath neuro-development treatment or only with the Bobath therapy? (2) Can a general increase in activity be obtained by the electrotherapeutic muscle stimulation? A test group (combined Hufschmidt/Bobath therapy) and a control group (Bobath), both consisting of 10 subjects, were observed for four months. The duration of observation was divided into two four months treatment periods with a rest interval of two months in between. At the start of therapeutic measures, motor activity and psychic condition were tested with corresponding motormetric and psychodiagnostic techniques; three check-up examinations were carried out at the end of the first, and at the beginning and end of the second period of treatment. The motor-metric control examination showed that at the end of the first period the test group had achieved by far the better results, but at the end of the second therapeutic period, both groups were equally successful. The combined electrophysiotherapy hence reached in a relatively shorter time - as it were by leaps and bounds - the optimal obtainable state of functional improvements which, with the Bobath therapy alone, can be effected more slowly but with more continuity. The psychodiagnostic controls clearly indicate that the electrical stimulation produced an unspecified increase in activity, especially after the first phase of treatment, whereas in the second phase this could only be proven in a graded form. The report closes with an examination of the results and their consequences for the implementation of the treatment for cerebral palsied children.

Cerebral Palsy↗
PubMed1988

Electric organ discharge frequencies from two weakly electric gymnotiform fish exposed to carbon dioxide, conductivity and pH changes.

Electric organ discharge (EOD) frequencies of two weakly electric, gymnotiform, water-breathing fish decreased abruptly with an increase in carbon dioxide concentration and decrease in pH, caused by bubbling carbon dioxide in water. After carbon dioxide bubbling ceased, the recovery of EOD frequencies was linear with the return toward normal pH, but with a lag, so that the frequency was below normal even 24 h after pH returned to the control value. In another series of experiments, blood collected by cardiac puncture after carbon dioxide bubbling was cut off showed pH values below normal, indicating a lag in the blood buffering capability. Conductivity of the water did not influence EOD frequency.

Animals↗
PubMed1986

Induction of ELF transmembrane potentials in relation to power-frequency electric field bioeffects in a plant root model system. II. The effect of 60 Hz electric fields on the growth of different regions of the cucurbit root elongation zone.

The region of elongation in Cucumis sativus and Cucurbita maxima roots was marked at increasing distances from the apex to provide an analog of increasing cell size. These roots were exposed/sham-exposed to 60 Hz electric fields and the growth rates of the root segments measured. The growth rate effect magnitude varied with increasing distance from the root tip at constant field strength, and with increasing applied field strength. These results provide strong, qualitative support for the postulate that ELF transmembrane potential induction is involved in the stimulation of ELF electric field effects in the plant root model system.

Cell Division↗
PubMed1978

The larval electric organ of the weakly electric fish Pollimyrus (Marcusenius) isidori (Mormyridae, Teleostei).

The larval electric organ of Pollimyrus isidori consists of four longitudinal tubes, a dorsal and a ventral pair, which begin behind the skull, end at the beginning of the caudal peduncle and show myotomic segmentation. The elementary units are, apparently, transformed muscle fibres called electrocytes. They are shorter and thicker than muscle fibres, with long stalks and are found in the medial part of the deep lateral muscle. Electron microscopy reveals a clear difference between the anterior and posterior face of the electrocyte. Anteriorly, deep linear invaginations of the surface membrane together with many small vesicles of about 100 nm diameter can be seen. Posteriorly, many plasma membrane invaginations and vacuoles are found together with numerous cytoplasmic organelles--pleiomorphic nuclei, Golgi apparatus, oblong mitochondria and multivesicular bodies. The stalk originates at the posterior face and the nerve terminals are situated at the distal end of the stalk. In the electrocyte, myofibrils, similar to those found in muscle fibres, can be detected with clearly visible Z lines but with only a suggestion of H zones. Two bundles of myofibrils can be seen arranged orthogonally in the electrocyte. Strong acetylcholinesterase activity was found on the anterior face and on the innervated stalk. Under the given recording conditions the overall discharge amplitude of the larval electric organ reaches a maximum of about 100 mV peak to peak. The pulse duration is 1 millisecond and the main phase is head-positive.

Animals↗
PubMed1993

Frequency domain electrical conductivity measurements of the passive electrical properties of human lymphocytes.

An extensive set of electrical conductivity measurements of human lymphocyte suspensions has been carried out in the frequency range from 1 kHz to 100 MHz, where the surface polarization due to the Maxwell-Wagner effect occurs. The data have been analyzed according to well-established heterogeneous system theories and the passive electrical parameters of both the cytoplasmic and nuclear membranes have been obtained. Moreover, a further analysis to take into account the roughness of the membrane surface on the basis of a fractal model yields new estimates for the membrane conductivity and the membrane permittivity, independently of the surface architecture of the cell. These findings are confirmed by measurements carried out at higher frequencies, in the range from 1 MHz to 1 GHz, on lymphocytes dispersed in both hyperosmotic and hypoosmotic media, that influence the surface complexity of the membrane due to the microvillous protrusions. The surface roughness of the cell is described by a macroscopic parameter (the fractal dimension) whose variations are associated to the progressive swelling of the cell, as the osmolality of the solution is changed.

Cell Membrane↗
PubMed1985

Autophagic sequestration of [14C]sucrose introduced into isolated rat hepatocytes by electrical and non-electrical methods.

Isolated rat hepatocytes were found to become permeable to [14C]sucrose at 0 degree C under three different conditions: Immediately following their liberation from the collagenase-perfused liver. Following a short incubation under hypoxic conditions. After electropermeabilisation. All three conditions were characterised by the formation of small protuberances (blebs) indicative of localised cell surface damage, and it is possible that the stretched plasma membrane of such blebs acted as a high-permeability region. Disappearance of blebs and restoration of normal plasma membrane impermeability could be achieved by a short (15 min) incubation at 37 degrees C. It could be shown that [14C]sucrose introduced into rat hepatocytes by non-electrical means was autophagically sequestered at the same rate as [14C]sucrose introduced electrically. In both cases the sequestration was inhibited by the specific autophagy inhibitor 3-methyladenine to a similar extent. The subcellular distribution of sequestered isotope in metrizamide/sucrose density gradients was found to be independent of the conditions of its introduction into cells.

Adenine↗
PubMed1993

Electrical burns caused by fishing rod contact with overhead electric cables: a potential hazard to fishermen.

Three patients were admitted to the Burns Unit at Newcastle General Hospital suffering from varying degrees of electrical burn injuries. All were fishermen whose injuries had been caused by their highly conductive carbon fibre fishing rods touching overhead high voltage electrical cables. This paper also describes the information available to fishermen to assist in the prevention of this type of injury.

Adult↗
PubMed2000

Immediate reinitiation of atrial fibrillation after electrical cardioversion predicts subsequent pharmacologic and electrical conversion to sinus rhythm and amiodarone.

Ninety-one percent of patients with atrial fibrillation (AF) resisting electrical cardioversion because of immediate reinitiation of AF after the shock maintain long-term sinus rhythm with amiodarone and repeat cardioversion. Thus, immediate reinitiation of AF is an important sign that should guide further treatment in patients with electrical cardioversion-resistant AF.

Amiodarone↗
PubMed1999

Roles of electric field and fiber structure in cardiac electric stimulation.

This study investigated roles of the variation of extracellular voltage gradient (VG) over space and cardiac fibers in production of transmembrane voltage changes (DeltaV(m)) during shocks. Eleven isolated rabbit hearts were arterially perfused with solution containing V(m)-sensitive fluorescent dye (di-4-ANEPPS). The epicardium received shocks from symmetrical or asymmetrical electrodes to produce nominally uniform or nonuniform VGs. Extracellular electric field and DeltaV(m) produced by shocks in the absolute refractory period were measured with electrodes and a laser scanner and were simulated with a bidomain computer model that incorporated the anterior left ventricular epicardial fiber field. Measurements and simulations showed that fibers distorted extracellular voltages and influenced the DeltaV(m). For both uniform and nonuniform shocks, DeltaV(m) depended primarily on second spatial derivatives of extracellular voltages, whereas the VGs played a smaller role. Thus, 1) fiber structure influences the extracellular electric field and the distribution of DeltaV(m); 2) the DeltaV(m) depend on second spatial derivatives of extracellular voltage.

Animals↗
PubMed1980

Organization of thiol groups of electric-eel electric-organ sodium-plus-potassium ion-stimulated adenosine triphosphatase studied with bifunctional reagents.

The reactions of three bifunctional thiol-blocking reagents of differing cross-linking spans and two monofunctional thiol-blocking reagents with the Na+ + K+-stimulated ATPase of the electric-eel electric organ were examined. 1,5-Difluoro-2,4-dinitrobenzene with a cross-linking span of 0.3--0.5 nm (3--5 A) and high solubility in non-polar solvent was the most efficient inhibitor of enzyme activity; thus essential thiol groups exist in a non-polar environment and are approx. 0.3--0.5 nm (3--5 A) from their nearest thiol-group neighbours. Ligands promoting phosphorylation of the Na+ + K+-stimulated ATPase decreased the number of thiol groups bridged by 1,5-difluoro-2,4-dinitrobenzene and by 4,4'-difluoro-3,3'-dinitrodiphenyl sulphone [0.7--1.0 nm (7--10 A) span]. Phosphorylation is associated with a conformational change in the enzyme.

Animals↗
PubMed1991

Association of the HNK-1 epitope with 5'-nucleotidase from Torpedo marmorata (electric ray) electric organ.

5'-Nucleotidase isolated from the electric organ of the electric ray (Torpedo marmorata) has a molecular mass of 62 kDa and, on two-dimensional electrophoresis, separates into up to 13 isoforms within a pI range of 5.9-6.7. The N-terminal sequence data show a 71% identity over 17 amino acids with that previously published for the rat liver enzyme. All forms of 5'-nucleotidase are recognized by the HNK-1 monoclonal antibody. HNK-1 immunoreactivity is found at the surface of the Schwann-cell processes covering the synaptic terminals and in this respect corresponds to that of 5'-nucleotidase in the same tissue. Since a number of glycoproteins involved in cell recognition and cell adhesion carry the HNK-1 epitope, 5'-nucleotidase may play a role in cell-cell or cell-extracellular matrix interaction in addition to its activity as an enzyme.

5'-Nucleotidase↗
PubMed1993

Structure of the glycosyl-phosphatidylinositol membrane anchor of acetylcholinesterase from the electric organ of the electric-fish, Torpedo californica.

The structure of the glycan moiety of the glycosyl-phosphatidylinositol (GPI) membrane anchor from Torpedo californica (electric fish) electric-organ acetylcholinesterase was solved using n.m.r., methylation analysis and chemical and enzymic micro-sequencing. Two structures were found to be present: Glc alpha 1-2Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN alpha 1-6myo-inositol and Glc alpha 1-2Man alpha 1-2Man alpha 1-6(GalNAc beta 1-4)Man alpha 1-4GlcN alpha 1-6myo-inositol. The presence of glucose in this GPI anchor structure is a novel feature. The anchor was also shown to contain 2.3 residues of ethanolamine per molecule.

Acetylcholinesterase↗
PubMed2002

Effect of electrical stimulation of the nucleus of the solitary tract on the development of electrical amygdaloid kindling in the cat.

PURPOSE: This work analyzed the effect of electrical stimulation of the nucleus of the solitary tract (NTS) on the development of electrical amygdaloid kindling (AK) in freely moving cats. METHODS: Nine male adult cats with implanted electrodes in both amygdalae (basolateral nucleus), both lateral geniculate bodies, left NTS, and both prefrontal cortices were used. Electromyogram and electrooculogram also were recorded. The AK was performed every 24 h (1-s train, 1-ms pulses, 60 Hz, 300-600 microA). The NTS was stimulated previously for 1 min (0.5-ms pulses, 30 Hz, 150-300 microA), just before the AK at 10:00 a.m., and then every 60 min, 4 times, from 11:00 a.m. to 2:00 p.m. On different days, all NTS stimulation was suspended, and AK was continued until stage VI kindling was reached. RESULTS: Behavioral changes produced by the stimulation of the NTS were blinking, immobility periods with upward sight, licking, and swallowing. Animals with simultaneous stimulation of NTS and AK did not reach stage VI, remaining in behavioral stages I-III. Stage VI was reached after NTS stimulation was intentionally suspended. The amplitude, duration, and the propagation of the amygdaloid afterdischarge did not exhibit progressive evolution during NTS stimulation. A regression analysis was performed between the number of days with only AK stimulation and days with simultaneous NTS stimulation, which showed a positive correlation (values of r = 0.84). CONCLUSIONS: Our results suggest that NTS stimulation interferes with the development of convulsive evolution and secondary generalization. This delay effect may be due to the activation of the locus ceruleus and some areas of the midbrain reticular formation, among other structures, which has been demonstrated to inhibit experimental convulsive seizures.

Amygdala↗
PubMed1972

Purification by affinity chromatography of the molecular forms of acetylcholinesterase present in fresh electric-organ tissue of electric eel.

An acetylcholinesterase inhibitor-Sepharose conjugate was prepared by coupling a derivative of the powerful acetylcholinesterase inhibitor, N-methylacridinium, to CNBr-activated Sepharose. Use of this conjugate permitted direct purification, by affinity chromatography, of the two molecular forms of acetylcholinesterase, 14 and 18 S, present in fresh electric organ tissue. The purified 14S and 18S acetylcholinesterases retained the capacity to aggregate at low ionic strength displayed by crude extracts of the enzyme. The major polypeptide components of the 14S and 18S enzymes, as revealed by acrylamide gel electrophoresis, closely resemble those observed in the 11S form of acetylcholinesterase, previously purified after tryptic digestion of electric-organ tissue.

Acetylcholinesterase↗