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PubMed1996

Determining blood and plasma volumes using bioelectrical response spectroscopy.

We hypothesized that an electric field (inductance) produced by charged blood components passing through the many branches of arteries and veins could assess total blood volume (TBV) or plasma volume (PV). Individual (N = 29) electrical circuits (inductors, two resistors, and a capacitor) were determined from bioelectrical response spectroscopy (BERS) using a Hewlett Packard 4284A Precision LCR Meter. Inductance, capacitance, and resistance from the circuits of 19 subjects modeled TBV (sum of PV and computed red cell volume) and PV (based on 125I-albumin). Each model (N = 10, cross validation group) had good validity based on 1) mean differences (-2.3 to 1.5%) between the methods that were not significant and less than the propagated errors (+/- 5.2% for TBV and PV), 2) high correlations (r > 0.92) with low SEE (< 7.7%) between dilution and BERS assessments, and 3) Bland-Altman pairwise comparisons that indicated "clinical equivalency" between the methods. Given the limitation of this study (10 validity subjects), we concluded that BERS models accurately assessed TBV and PV. Further evaluations of the models' validities are needed before they are used in clinical or research settings.

Adult↗
PubMed1989

Lumbar sympathetic ganglia in man: an electrophysiological study in vitro.

A method has been developed for the removal, preservation and electrophysiological study 'in vitro' of sympathetic lumbar chains (L1-L3) from subjects undergoing lumbar ganglionectomy in the treatment of peripheral vascular diseases. Extracellular recordings from interganglionic trunks, and intracellular recordings from single sympathetic neurons, were performed. The extracellular experiments substantiated the concept, hitherto deduced from animal experiments, that the preganglionic fibres in the sympathetic lumbar chain are mainly of a descending nature. In fact, stimulation of the interganglionic trunk cranial to ganglia is always much more effective in driving ganglion neurons to fire than stimulation of the interganglionic trunk caudal to ganglia. The intracellular experiments produced a good definition of the main electrical characteristics of human sympathetic neurons. The results can be summarized as follows: the resting membrane potential ranged from 50 to 75 mV (63.4 +/- 9.2 mV; 21 neurons); action potential amplitude from 62 to 93 mV (74.3 +/- 8.1 mV; 27 neurons); membrane input resistance was 42.3 +/- 12.6 m omega (8 neurons) and total membrane capacitance 83.7 +/- 15.3 pF (8 neurons).

Action Potentials↗
PubMed1970

Linear electrical properties of the transverse tubules and surface membrane of skeletal muscle fibers.

With the use of two intracellular microelectrodes and a circuit designed to compensate for the effects of stray capacitances around the electrodes, transfer impedance measurements were made at frequencies from 0.5 to 1000 c/s on frog sartorius muscle fibers bathed in 7.5 mM K Ringer solution. Complete AC cable analyses performed at 46, 100, 215, 464, and 1000 c/s showed that the fibers behaved as ideal one-dimensional cables having purely resistive internal impedances (R(i) = 102 +/- 11 Omega cm). Two circuits were considered for fiber inside-outside impedance, a four lumped parameter circuit and a parallel resistance and capacitance shunted by the input impedance of a lattice model for the T-system. Least squares fits to fiber input impedance phase angles were better with the latter circuit than with the former. With the use of the lattice model the specific capacitance of both the surface and transverse tubule membranes was found to be 1 microF/cm(2) and the internal resistivity of the tubules to be about 300 Omega cm.

Animals↗
PubMed1976

Electromechanical coupling in tubular muscle fibers. II. Resistance and capacitance of one transverse tubule.

In tubular muscle fibers of the yellow scorpion the transverse tubules are arranged in a radial symmetry. This particular morphology, enables one to derive values for electrical components of one transverse tubule (TT) by treating the TT as a core conductor rather than a complex network. The electrical properties of tubular muscle fibers were completely characterized and analyzed by measuring two independent functions of frequency, i.e., the characteristic impedance and the propagation function. The impedance of a single tubular muscle fiber was determined with microelectrodes over the frequency range 1 Hz to 1.5 kHz. The results were fitted to a possible equivalent circuit model which is based on morphological evidence. The average component values for this model are: Ri = 209 omega-cm, Rm, and RT = 980 omega-cm2 (referred to unit area of surface membrane), Cm and CT = 0.9 muF/cm2, and RL = 103 omega-cm. Relating the equivalent circuit to ultrastructure shows that the average component values are consistent with the hypothesis that the TT is open to the extracellular medium, the electrical capacity of surface and TT membranes is about 1 muF/cm2, and the spread of surface depolarization into the TT is attenuated by about 25%.

Animals↗
PubMed2003

An approach to electrical modeling of single and multiple cells.

Previous theoretical approaches to understanding effects of electric fields on cells have used partial differential equations such as Laplace's equation and cell models with simple shapes. Here we describe a transport lattice method illustrated by a didactic multicellular system model with irregular shapes. Each elementary membrane region includes local models for passive membrane resistance and capacitance, nonlinear active sources of the resting potential, and a hysteretic model of electroporation. Field amplification through current or voltage concentration changes with frequency, exhibiting significant spatial heterogeneity until the microwave range is reached, where cellular structure becomes almost "electrically invisible." In the time domain, membrane electroporation exhibits significant heterogeneity but occurs mostly at invaginations and cell layers with tight junctions. Such results involve emergent behavior and emphasize the importance of using multicellular models for understanding tissue-level electric field effects in higher organisms.

Cells↗
PubMed1993

Lumped-parameter model for in vivo cochlear stimulation.

This paper presents a lumped-parameter model that stimulates the in vivo electrical properties of a guinea pig cochlea implanted with a multielectrode stimulating array. A basic model of the low-frequency electroanatomy in a normally functioning guinea pig cochlea is developed by adding critical membrane capacitances to Strelioff's resistive network model [1]. The basic model of normal cochlear tissues is modified to account for anatomical and physiological differences between a normal and implanted cochlea, which results in an impedance model of an implanted cochlea. Simulating the results of in vivo cochlear stimulation verifies the accuracy with which the modified cochlear model represents electrical properties within an electrically stimulated cochlea. Generalized simulations using this model suggest a straightforward phasing scheme capable of achieving sharply focused, channel-independent multielectrode cochlear stimulation.

Animals↗
PubMed1984

Membrane electrical properties of developing fast-twitch and slow-tonic muscle fibres of the chick.

Isolated single fibres from the anterior (a.l.d.) and the posterior (p.l.d.) lattissimus dorsi muscles of embryonic and young chicks were used to study in vivo development of membrane electrical properties. Isolated fibres were obtained by an enzymatic dissociation procedure. Intracellular micro-electrode recordings from isolated fibres and from fibres in intact muscles showed that the dissociation procedure did not significantly alter resting membrane potentials, input resistances or membrane time constants (tau m). The 14 day embryonic fibres of a.l.d. and p.l.d. did not have a measurable resting conductance to Cl-. At hatching, about 70% of the resting conductance in p.l.d. fibres was due to Cl-. Membrane electrical properties were estimated from the analysis of voltage responses to intracellular injection of rectangular pulses of current. At 14 days in ovo, membrane resistance (Rm) was approximately 20 k omega cm2 and membrane capacitance (Cm) was 1-2 microF/cm2 for both a.l.d. and p.l.d. The mean membrane length constants (lambda) were 1.7 mm for a.l.d. and 1.5 mm for p.l.d. For p.l.d., the values of Rm, tau m and lambda decreased as development proceeded. For a.l.d., there was no change in these values by the time of hatching (21 days). The decreases in the electrical constants for p.l.d. fibres were partly explained by the appearance of a resting Cl- conductance during the last week of embryonic development.

Animals↗
PubMed2005

Electrical and spectroscopic characterization of metal/monolayer/Si devices.

A simple technique for vibrational spectroscopy of metal/monolayer/silicon structures is applied to study the interaction of Au, Al, and Ti with alkane monolayers, either assembled onto thin oxides or directly attached to Si. The results are correlated with current-voltage and capacitance-voltage measurements. Alkane films on oxides are found to be robust with respect to the deposition of Au and Al and are partially consumed during the deposition of Ti. In contrast, alkoxy films directly attached to H-terminated Si via an ether linkage are displaced by all three metals. The vibrational data are positively correlated with the electrical data to establish an improved understanding of the interactions at the buried metal/monolayer interface. The results demonstrate extreme sensitivity of the monolayer/metal reactivity to the nature of the film/substrate bonding.

Journal Article↗
PubMed1994

cAMP-enhancing agents "permit" stimulus-secretion coupling in canine pancreatic islet beta-cells.

Isolated canine islets of Langerhans differ from isolated islets of other species (including rodents and man) in that elevated glucose concentrations are unable to stimulate insulin secretion. Here we demonstrate that addition to the perifusate of isobutylmethylxanthine (IBMX), forskolin or 8-CPT-cAMP, all of which enhance cytosolic cAMP, permits insulin secretion in response to glucose, leucine or tolbutamide. These cAMP enhancers increase secretogogue-induced electrical activity in beta-cells and restore depolarization-induced, Ca(2+)-dependent granule exocytosis measured as stepwise increases in membrane capacitance. We propose that the primary permissive action of cAMP is to tightly link Ca2+ entry to insulin granule release, while a secondary action is to tighten the link between glucose metabolism and cell depolarization.

1-Methyl-3-isobutylxanthine↗
PubMed1972

The transient response and impedance locus of a mobile site membrane.

The kinetic properties of a mobile site membrane are analyzed theoretically and the results are compared with experimental data obtained from a simple model system. In the model system the measured response to a step change in electric current is a single relaxation process, in excellent agreement with the theoretically predicted behavior. To this relaxation process corresponds an anomalous capacitance whose properties are obtained by performing a frequency analysis of the system. By plotting the impedance locus of this mobile site membrane, the locus is shown to exhibit a 45 degrees phase angle at high frequencies, a phenomenon which is generally associated with depletion layers.

Binding Sites↗
PubMed1996

Comparison of chaotic and sinusoidal vasomotion in the regulation of microvascular flow.

OBJECTIVE: In order to elucidate the physiological consequences of irregular vasomotion on microvascular flow we have compared the theoretical hydrodynamic consequences of sinusoidal and chaotic fluctuations in the diameter of a single resistance vessel. METHODS: In initial experimental studies vasomotion was induced by histamine in isolated rabbit ear resistance arteries (approximately 150 microns diameter) perfused with physiological buffer under both controlled-flow and controlled-pressure conditions. The phase relationships between the observed oscillations in flow and pressure were used to validate a theoretical electrical circuit in which vasomotion was simulated as sinusoidal or as chaotic fluctuations in distal resistance, with compliance incorporated as a parallel capacitance. RESULTS: In both the experimental and theoretical situation, oscillations in flow led those in pressure by approximately 90 degrees in controlled-flow mode, whereas they were approximately 180 degrees out of phase in controlled-pressure mode. In the theoretical model an increase in the amplitude of sinusoidal or chaotic diameter fluctuations enhanced flow, but "paradoxically" increased both time-averaged resistance and conductance. The model showed that with sinusoidal fluctuations the "efficiency" of perfusion (i.e., flow/viscous work expended in perfusing the vessel undergoing vasomotion) exhibited a peak whose magnitude was a function of vasomotion amplitude and the proximal capacitance in the circuit, and was attributable to transient release of charge from this capacitance. This phenomenon was not observed in simulations with chaotic vasomotion. Hydrodynamic effects specific to the presence of chaotic dynamics (e.g., abrupt increases or decreases in flow under the variation of a single parameter) were also evident when the intrinsic complexity of the vasomotion, rather than its amplitude, was varied. CONCLUSIONS: The model suggests (i) that vasomotion may serve to increase flow, (ii) that conductance provides a more accurate physiological measure of the functional consequences of active vasomotion than resistance, (iii) that chaotic vasomotion dissipates transients more readily than sinusoidal vasomotion, thereby conferring greater stability to microcirculatory perfusion and (iv) that specific modes of chaotic vasomotion may influence flow independently of their amplitude.

Animals↗
PubMed1999

Leishmania amazonensis infection induces changes in the electrophysiological properties of macrophage-like cells.

Whole cell patch-clamp recordings were used to study the electrical properties of the macrophage-like cell line J774.1, after infection with Leishmania amazonensis. Infection induced a significant increase in cell size and membrane capacitance, suggesting that parasite invasion leads to the addition of plasma membrane to the host cell. By 24 hr after infection, the host cell membrane potential was significantly more hyperpolarized than control cells, and this difference remained for the subsequent 72 hr post-infection. The hyperpolarization was paralleled by an increase in the density of inward rectifying K(+) currents. The shape of the conductance vs. voltage curve, the kinetic properties and the pharmacological profile of these currents were not significantly altered by infection. These results suggest that infection by L. amazonensis causes an increase in the number of functional inward rectifying K(+) channels, leading to hyperpolarization of the host cell membrane.

Animals↗
PubMed1994

Effects of chronic spinalization on ankle extensor motoneurons. III. Composite Ia EPSPs in motoneurons separated into motor unit types.

1. In this paper we continue an examination of changes in composite Ia excitatory postsynaptic potentials (EPSPs) in ankle extensor motoneurons after 6-wk (L1-L2) spinal cordotomy. The ratio of rheobase to input resistance was used to divide motoneurons into three groups approximating fast-fatigable (FF), fast fatigue-resistant (FR), and slow (S) motor units in barbiturate-anesthetized cats. Homonymous monosynaptic Ia EPSPs evoked by low-strength [1.2 times threshold (T)] electrical stimulation and heteronymous EPSPs evoked by 2T stimulation were compared between groups of motoneurons in unlesioned and chronic spinal preparations. 2. The distribution of motor unit types of triceps surae and plantaris (PL) motoneurons according to the present classification scheme agrees well with that obtained elsewhere using mechanical typing. Chronic spinalization resulted in an increased proportion of type FF motoneurons in PL and type FR motoneurons in lateral gastrocnemius (LG) motoneurons. There was a numeric but insignificant increase in the proportion of fast medial gastrocnemius motor units. 3. Membrane time constant (tau m) and estimated total cell capacitance were significantly reduced in FF and S motoneurons in chronic spinal preparations. FF motoneurons from chronic spinal animals also had a reduced afterhyperpolarization duration. Mean values of membrane electrical properties in FR motoneurons were unaltered after spinalization. 4. Homonymous Ia EPSP changes after chronic spinalization occurred preferentially in type FR and S motor units. Amplitudes increased 69% in type FR and 38% type S motor units but were unchanged in type FF units. Furthermore, the amplitudes of heteronymous Ia EPSPs in type FF and S units in the chronic spinal preparation were almost double those in unlesioned preparations. 5. Homonymous EPSP 10-90% rise times decreased 25% in type FR motor units and 15% in type S motor units and were unchanged in type FF motor units. Homonymous EPSP half-width decreased in all three motoneuron groups. Normalization of EPSP rise time and half-width to tau m reduced the difference between EPSP shape indexes in unlesioned and chronic spinal preparations in type FF and S motoneurons but less so in type FR motoneurons. Normalized EPSP shape indexes in some type FR units were shorter after chronic spinalization than any in unlesioned preparations. 6. The increased amplitude and decreased rise time of Ia EPSPs in type FR motoneurons after spinalization occurred without changes in the electrical properties of type FR motor units.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Cisplatin: effects on the stretch receptor neuron of the crayfish.

The effects of cisplatin on electrical and mechanotransducer properties of the crayfish stretch receptor neuron was studied using a microelectrode voltage clamp technique. In the stretch receptor neuron, negligible changes in membrane capacitance, leak conductance, resting membrane potential, potential-dependent currents or mechanoreceptor current were seen either on acute cisplatin treatment or after long-lasting treatment for up to 2 weeks. The inhibitory GABA-sensitive synapse on the neuron was not affected by cisplatin. The cisplatin cytotoxicity on sensory neurons such as outer hair cells of the organ of Corti cannot be explained by direct effects on ionic channels of these cells including stretch-activated channels.

Animals↗
PubMed1981

The molecular organisation of bimolecular lipid membranes. The dielectric structure of the hydrophilic/hydrophobic interface.

Improvements to a previously described very low-frequency impedance-measuring technique have now allowed the characterisation of a third, electrically distinct, type of substructural region in phosphatidylcholine biomolecular lipid membranes. This region was found to have properties intermediate to those of the hydrophobic (hydrocarbon) layer and the regions containing the polar heads of the phosphatidylcholine molecules. Its properties are consistent with it being associated with the oxygen-rich carboxyl ester portions of the phosphatidylcholine molecules which lie at the hydrophilic/hydrophobic interface. We will refer to these regions in the membrane as the acetyl regions. The individual properties of the three distinct types of region in the phosphatidylcholine membranes were determined at KCl electrolyte concentrations of 1, 10, 100 and 1000 mM. It was found that with increasing KCl concentration: (a) The capacitance, CH, of the hydrophobic region increased slightly, indicating a decrease in the thickness of this region. (b) The conductance, GH, of this hydrophobic region increased by a factor of 20 in going from 1 to 1000 mM electrolyte. (c) The capacitance of the acetyl region was independent of KCl concentration although its conductance increased 5-fold over the range 1-1000 mM KCl. (d) The volume-specific electrical properties of the region containing the polar heads appeared to be essentially independent of KCl concentration. However, a change in thickness of these regions was observed which was consistent with the cholinephosphate dipole being oriented normal to the bilayer surface in 1 mM KCl and parallel to the surface in 1000 mM KCl external solutions.

Electric Conductivity↗