Biomedical subjects

V Krauthamer

Publications and source records attributed to V Krauthamer.

At least 19 recordsLinked to original sources

PubMed2004

Acute effects of adrenergic agents on post-defibrillation arrest time in a cultured heart model.

Possible drug interactions with electrical defibrillation were examined. We tested the hypothesis that adrenergic agents (epinephrine, norepinephrine, isoproterenol) and a calcium channel blocker (verapamil), when applied acutely, alter the duration of arrest following a defibrillator shock. A secondary hypothesis (based on observations) was that the drugs alter the occurrence of changes to normal rhythms following the shock. Dissociated heart cells from 10-day chicken embryos were cultured to form spherical aggregates and plated in petri dishes. In the experiments, the spheres were paced at 0.75 V/cm above contraction threshold, and a biphasic defibrillator shock was applied for 1 ms at 46 V/cm. The arrest time and occurrence of rhythm changes were recorded. The adrenergic agents shortened the duration of arrest following a defibrillator shock, while the calcium channel blocker lengthened the arrest time. Comparisons with the control proportion of double beats showed no significant change with the adrenergic agents and a decrease with verapamil.

Adrenergic Agents↗

PubMed2002

Effects of high-rate electrical stimulation upon firing in modelled and real neurons.

Many medical devices use high-rate, low-amplitude currents to affect neural function. This study examined the effect of stimulation rate upon action potential threshold and sustained firing rate for two model neurons, the rabbit myelinated fibre and the unmyelinated leech touch sensory cell. These model neurons were constructed with the NEURON simulator from electrophysiological data. Alternating-phase current pulses (0-1250 Hz), of fixed phase duration (0.2 ms), were used to stimulate the neurons, and propagation success or failure was measured. One effect of the high pulse rates was to cause a net depolarisation, and this was verified by the relief of action potential conduction block by 500 Hz extracellular stimulation in leech neurons. The models also predicted that the neurons would maintain maximum sustained firing at a number of different stimulation rates. For example, at twice threshold, the myelinated model followed the stimulus up to 500 Hz stimulation, half the stimulus rate up to 850 Hz stimulation, and it did not fire at 1250 Hz stimulation. By contrast, the unmyelinated neuron model had a lower maximum firing rate of 190 Hz, and this rate was obtained at a number of stimulation rates, up to 1250 Hz. The myelinated model also predicted sustained firing with 1240 Hz stimulation at threshold current, but no firing when the current level was doubled. Most of these effects are explained by the interaction of stimulus pulses with the cell's refractory period.

Animals↗

PubMed2000

Electrostimulators for acupuncture: safety issues.

Three representative electrostimulators were evaluated to determine whether they meet the manufacturers' labeled nominal output parameters and how the measured parameters compare with a safety standard written for implanted peripheral nerve stimulators. The pulsed outputs (pulse width, frequency, and voltage) of three devices were measured with an oscilloscope across a 500-ohm resistance, meant to simulate subdermal tissue stimulated during electroacupuncture. For each device, at least two measured parameters were not within 25% of the manufacturer's claimed values. The measured values were compared with the American National Standard ANSI/AAMI NS15 safety standard for implantable peripheral nerve stimulators. Although for two stimulators the pulse voltage at maximum intensity was above that specified by the standard, short-term clinical use may still be safe because the standard was written for long-term stimulation. Similarly, the net unbalanced DC current, which could lead to tissue damage, electrolysis, and electrolytic degradation of the acupuncture needle, was within the limits of the standard at 30 pulses per second, but not at higher frequencies. The primary conclusions are (1) that the outputs of electrostimulators must be calibrated and (2) that practitioners must be adequately trained to use these electrostimulators safely.

Electric Stimulation↗

PubMed1997

BAPTA-AM and ethanol protect cerebellar granule neurons from the destructive effect of the weaver gene.

The mechanisms by which the weaver gene (Reeves et al., 1989; Patil et al., 1995) inhibits neurite extension and/or induces death of the granule neurons in homozygous weaver mouse cerebellum are not presently understood. Here we show that BAPTA-AM and ethanol, which either reduce cytosolic levels of free calcium or prevent calcium entry, promote neurite outgrowth of the weaver neurons similar to the L-type calcium channel blocker verapamil (Liesi and Wright, 1996). Importantly, BAPTA-AM, ethanol, and verapamil not only restore neurite outgrowth of the weaver neurons but adjust their depolarized resting membrane potentials to the levels of normal neurons. These results indicate that calcium-dependent mechanisms mediate the action of the weaver gene and that the weaver neurons can be normalized by blocking this calcium effect. We further report that BAPTA-AM and verapamil also have a neuroprotective effect on normal neurons exposed to high concentrations of ethanol. We suggest that verapamil should be evaluated as a drug for treatment of alcohol-induced brain damage and neurodegenerative disorders.

Animals↗

PubMed1997

Calcium dynamics in cultured heart cells exposed to defibrillator-type electric shocks.

Spatial and temporal changes in intracellular calcium ion concentration and transmembrane voltage were recorded optically from single-isolated cultured chick-embryo heart cells exposed to high-voltage, defibrillator-type shocks. Fluorescence changes were measured during 5 msec electric shocks of field strengths up to 56 volts/cm in single myocytes stained with a Ca(++)-sensitive or voltage-sensitive dye. Shocks caused a reversible period of depolarization, elevated cytosolic Ca++, and refractoriness. Intracellular Ca++ elevation had two temporal phases: first, a Ca++ spike with morphology independent of shock intensity; and second, a prolonged Ca++ elevation with a shock-intensity-dependent magnitude and duration, and with greatest Ca++ elevation at the poles of the cell adjacent to the electrodes. The prolonged elevation (second phase) was initiated earlier at the anode-facing pole of the cell than at the cathode-facing pole. These results suggest that postshock Ca++ entry consists of two parts: early normal entry through excitation channels plus a prolonged elevation which may be related to cellular damage.

Animals↗

PubMed1996

Spontaneous firing of NG108-15 cells induced by transient exposure to ammonium chloride.

1. We report that NG108-15 (neuroblastoma x glioma) cells differentiated in defined serum-free media are capable of exhibiting stable automaticity (the spontaneous occurrence of regenerative action potentials) following exposure to extracellular perfusates containing NH4Cl. 2. Membrane depolarization (4-5 mV) concomitant with an increased pHi during NH4Cl exposure are followed by hyperpolarization (5-7 mV), sub-threshold oscillations, and spontaneous firing after the removal of NH4Cl. 3. Cells cultured in 10% serum did not exhibit automaticity. Cells cultured in serum-free media are twice as likely to show automaticity as those cultured in reduced (1.5%) serum media. 4. We have examined factors that contribute to the events following NH4Cl exposure, namely, membrane depolarization and hyperpolarization, subthreshold oscillations, and automaticity. The inward currents activated at more negative potentials and the ionic currents associated with pronounced afterhyperpolarization in NG108-15 cells cultured in serum-free media provide a basis for the repetitive activity in general and automaticity in particular.

Amiloride↗

PubMed1995

Directional guidance of neurite outgrowth using substrates patterned with biomaterials.

The use of geometrically simple networks formed by cultured neurons facilitates the electrophysiological study of biological computation. We used chemically patterned substrates for culturing SK-N-SH human neuroblastoma cells and embryonic rat hippocampal neurons to geometrically control their neurite outgrowth. On patterned substrates (parallel lines, 5-10 microns width), the neuroblastoma cells developed bipolar morphology with long neurite processes (approximately 200 microns) in the presence of retinoic acid. Hippocampal neurons cultured on substrates of hexagonal patterns extended their neurites preferentially along the circumferences of the hexagons and formed geometrically well defined network structures.

Animals↗

PubMed1994

Use of chemically patterned substrate to study directional effect of damaging electrical stimulation on cultured neuroblastoma cells.

We used ordered arrangements of neuroblastoma cells in culture on chemically patterned substrates to direct the orientation of electrical stimulation with respect to cell alignment. Chemically patterned parallel lines of self-assembled monolayer films were fabricated on glass substrates via a deep UV lithographic procedure. Cultured neuroblastoma cells deposited on these substrates formed long (approximately 300 microns in length) neuritic processes along the patterned lines in the presence of retinoic acid. Cells attached to the surface of these substrates were placed in a stimulation chamber so that an electric field (1.4-1.9 V/cm) could be applied in the direction parallel or perpendicular to neuritic or orientation. A majority of cells aligned parallel to the orientation of electrical stimulation exhibited a variety of cellular responses including neuritic tip damage, reductions in neuritic length and varicosity formation. These effects were observed to a lesser degree on the cells when electrical stimulation with the same magnitude was applied perpendicularly to the cell alignment. This work supports earlier findings that geometry is a crucial factor in determining cellular response to applied electric fields and goes on to show that cellular orientation is a key factor in determining cellular damage in culture.

Electric Stimulation↗

PubMed1994

Two-point electrical-fluorescence recording from heart with optical fibers.

Optical recordings from frog myocardium, stained with a voltage-sensitive dye, have been made through a fiber optic system that uses fiber couplers to provide two excitation/detection paths and to separate excitation light from the fluorescence signal. The excitation light, from a green He-Ne laser (543 nm), is focused into a 100 microns-core fiber then is split 1:1 to two other fibers. Each of these two fibers transmits part of the excitation light through a fiber coupler (1:15 transmittance ratio) to the heart preparation which is stained with the voltage-sensitive dye RH237. The returning red fluorescence is split at the same fiber coupler (15:1 transmittance ratio) and is directed to a photomultiplier tube through a longpass filter. With this two-point mapping method, differences in action potential shape and timing have been observed.

Action Potentials↗

PubMed1993

Containment and growth of neuroblastoma cells on chemically patterned substrates.

Patterned substrates offer the promise of controlled positioning and directional guidance of growing neurites. Therefore, they could be useful for constructing small neuronal networks with defined geometry in vitro. We have fabricated chemically patterned substrates using self-assembled monolayer films with a lithographic mask technique and demonstrated the feasibility for geometrically patterning neuroblastoma cells in culture. N-octadecyltrichlorosilane (OTS) was chemically bonded to glass and fused silica substrates, rendering the surface hydrophobic and non-adhesive to cells. Using surface analysis techniques, we have confirmed that OTS films were true monolayers and can be photocleaved from the surface by deep UV irradiation. An adhesive pattern of n-(2-aminoethyl-3-aminopropyl)trimethoxysilane was formed on a selectively irradiated OTS surface via a deep UV lithographic procedure. The chemically patterned surface was then seeded with SK-N-SH human neuroblastoma cells, and cellular attachment and growth were monitored by optical microscopy. The use of 2-dimensional substrates supported the containment and growth of neuroblastoma cells within the pattern for at least 15 days in culture. These chemical patterns may also be useful in controlled arrangements of hearts cells or muscle cells on prosthetic implant devices.

Cell Adhesion↗

PubMed1991

Deep UV photochemistry of chemisorbed monolayers: patterned coplanar molecular assemblies.

Deep ultraviolet (UV) irradiation is shown to modify organosilane self-assembled monolayer (SAM) films by a photocleavage mechanism, which renders the surface amenable to further SAM modification. Patterned UV exposure creates alternating regions of intact SAM film and hydrophilic, reactive sites. The exposed regions can undergo a second chemisorption reaction to produce an assembly of SAMs in the same molecular plane with similar substrate attachment chemistry. The UV-patterned films are used as a template for selective buildup of fluorophores, metals, and biological cells.

Axons↗

PubMed1991

Excitation and detection of action potential-induced fluorescence changes through a single monomode optical fiber.

An optical probe capable of detecting intracellular potential changes in individual cells, in vitro, which has the potential for in vivo applications, has been developed. A single-mode optical fiber directs laser light onto cells stained with the voltage-sensitive fluorescent dye, WW781 and also returns part of the resulting fluorescence to a detection system. Frog cardiac cells in vitro were used in these initial experiments. The fractional change in fluorescent intensity of 10(-3) for a 50 mV shift in transmembrane potential obtained from a heart immobilized in zero calcium Ringer's solution is comparable to that reported for other optical methods. For hearts in normal calcium Ringer's solutions, very large reproducible motion related artifacts were detected.

Animals↗

PubMed1991

Morphological and electrophysiological changes produced by electrical stimulation in cultured neuroblastoma cells.

Electric fields, which were equivalent to those generated by medical devices, were applied to cultured neuroblastoma cells (mouse and human) to test for morphological damage and to establish damage thresholds. Each of two methods of applying fields permitted flow of electrical current and minimized exposure of cells to electrode-breakdown products. One method consisted of a pair of parallel wires in a Petri dish by which current was delivered within a fixed volume of flowing tissue-culture media. With the other method, the cells were held in a confined geometrical chamber and current was applied via agar bridges. Under a given set of stimulation parameters, damage was found to be variable from cell to cell. By changing the strength of the electric field (frequency and duration of stimulation held constant), thresholds of several V/cm were found above which cell damage could be reliably produced. Depending on the intensity of the field, damage took the form of cell lysis or damage to neurites. Intracellular recordings from the mouse neuroblastoma cells revealed a correlation between a decline in resting transmembrane potential and stimulus intensity. Human neuroblastoma cells were less susceptible to damage than were the mouse neuroblastoma cells, given the same strength of applied electric fields.

Animals↗

PubMed1990

Modulation of conduction at points of axonal bifurcation by applied electric fields.

This study investigated how weak electric fields, on the order of 100 mV/cm, modulate action potential conduction through points of axonal bifurcation in leech touch sensory neurons. Axonal branch points in neurons are ubiquitous structures, and they are sites of low safety-factor for action potential propagation. In this study calibrated electric fields were applied around excised ganglia from the leech central nervous system. The electric fields were generated by 500 ms constant current square waves applied to the bath containing the tissue. Microelectrode penetration of the neurons was used to: 1) record transmembrane potential changes in the cell body of the neuron that resulted from the external field; 2) monitor conduction block when action potentials, evoked in the periphery, propagated into the ganglion; 3) inject current directly into the cell in an experimental analysis of the mechanism by which the externally applied field produced block. Conduction block was reliably induced by electric fields too weak to reach threshold for firing action potentials. In an experimental analysis where block was produced by the direct intracellular injection of negative current, a reversed polarity field relieved it. This indicates that when the external field induces block, it does so by membrane hyperpolarization at the branch point.

Action Potentials↗

PubMed1989

Properties of barnacle photoreceptor cells in culture.

1. Properties of median photoreceptor cells in cultured ocelli from the giant barnacle (Balanus nubilus) were compared in isolated ocelli, ocelli maintained with the supraesophageal ganglion, and fresh ocelli. 2. Cultured photoreceptor cells exhibited slight deterioration after 2-4 weeks. Cell bodies maintained their structure but apparently lost some dendrites. Electron micrographs revealed fewer rhabdomeres. Axons did not degenerate. 3. Intracellularly recorded responses to light in both cultured preparations were qualitatively normal with a small decrease in sensitivity and increase in input resistance. The waveforms of the light responses were normal. 4. The characteristic shadow reflex was maintained after 6 weeks.

Animals↗

PubMed1985

Electrophysiology of identified neurosecretory and non-neurosecretory cells in the cockroach pars intercerebralis.

Two cell types can be distinguished with intracellular recording from the pars intercerebralis of the American cockroach (Periplaneta americana). The first type, which corresponds morphologically to the medial neurosecretory cell, always had spontaneously occurring, overshooting action potentials. These action potentials are probably endogenously produced. Tetrodotoxin experiments revealed that sodium is the dominant ion of the action potential. The action potentials are followed by a relatively long after-hyperpolarization. The input resistance of these cells ranged from 120 to 390 M omega. A mathematical model, based on cellular morphology and response to current pulses, revealed a membrane time constant of about 100 msec and an axonal:somatic conductance ratio of approximately 13. Area-specific membrane resistance was estimated at 33 k omega cm2. These cells also often had reversible and spontaneous inhibitory postsynaptic potentials. The second cell type, which is non-neurosecretory, never produced spontaneous action potentials and rarely had synaptic potentials. Action potentials could be evoked by current injection into the cell body or by extracellular stimulation of their axons in the posteroventral portion of the the protocerebrum. These action potentials also depend on sodium ions. Their input resistance ranged from 16 to 35 M omega. They had a membrane time constant of approximately 15 msec and an axonal:somatic conductance ratio of about 9. Their area specific membrane resistance was estimated at 14 k omega cm2.

Action Potentials↗

PubMed1985

Morphology of identified neurosecretory and non-neurosecretory cells in the cockroach pars intercerebralis.

Electrophysiologically identified cells of the cockroach pars intercerebralis (Periplaneta americana) were injected with the dye Lucifer Yellow for morphological examination and with horseradish peroxidase for ultrastructural marking. In addition to this, uninjected cells were also studied to elaborate the findings from the injected material. The two electrophysiologically distinct classes of cells (type I and type II) correspond to two distinct morphological and ultrastructural classes. Type I cells are the medial neurosecretory cells of the pars intercerebralis, which project their axons to the retrocerebral neuro-hemal complex. Their cell bodies have a mean diameter of 17 microns, and they contain neurosecretory granules 200 nm in diameter. Arborizations emanate from the axon in the anterior part of the protocerebral neuropil. The type II cell bodies are larger (38 microns in diameter). Their axons project into the contralateral circumesophageal connective. These cells were usually multipolar, having somatic arborizations in the anterior portocerebral neuropil. The cell bodies contain vesicles 40 nm in diameter, numerous trophospongia, and a multi-layered glial envelope.

Animals↗

PubMed1984

Optical measurements of potential changes in axons and processes of neurons of a barnacle ganglion.

Optical techniques using voltage-sensitive dyes were used to record electrical events simultaneously from many positions on certain neurons of the barnacle supraesophageal ganglion. By signal-averaging, recordings with good signal-to-noise ratios and time resolution were obtained from fine dendritic processes as well as the axon and cell body. Controls established that the optical signals faithfully matched recordings made with intracellular electrodes for short times (5 to 10 msec), but deviations were observed at longer times. Pharmacological effects and photodynamic damage due to the dye were insignificant. The optical records were correlated with positions on the stimulated cell determined from Lucifer Yellow injections. This comparison demonstrated that signal-averaged records with large signal-to-noise ratios were obtained from those parts of the visual field which contained elements of the stimulated cell and hence could be attributed to specific locations on the cell. The quality of the optical signals were adequate to: (a) determine variations in the shape of action potentials in different parts of the cell; (b) demonstrate electrotonic spread of hyperpolarizing pulses; (c) determine the direction and velocity of action potential propagation, and (d) in some circumstances, using reasonable assumptions, estimate variations in the amplitude of action potentials or electrotonic pulses in different regions of the cell.

Action Potentials↗