Comments on "the effects of the coronary capacitance on the interpretation of diastolic pressure-flow relationships" which appeared in circ. res. 50: 334-341, 1982.
Explore the source record for details and available documents.
Coronary Circulation↗
SEARCH · Search PubMed
Results for “Electric Capacitance”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
[Participation of the diencephalic structures in the regulation of the tonus of the capacitive and resistive vessels of the musculocutaneous region].
Explore the source record for details and available documents.
Animals↗
Influenza hemagglutinin-mediated fusion pores connecting cells to planar membranes: flickering to final expansion.
We have studied the fusion between voltage-clamped planar lipid bilayers and influenza virus infected MDCK cells, adhered to one side of the bilayer, using measurements of electrical admittance and fluorescence. The changes in currents in-phase and 90 degrees out-of-phase with respect to the applied sinusoidal voltage were used to monitor the addition of the cell membrane capacitance to that of the lipid bilayer through a fusion pore connecting the two membranes. When ethidium bromide was included in the solution of the cell-free side of the bilayer, increases in cell fluorescence accompanied tee admittance changes, independently confirming that these changes were due to formation of a fusion pore. Fusion required acidic pH on the cell-containing side and depended on temperature. For fusion to occur, the influenza hemagglutinin (HA) had to be cleaved into HA1 and HA2 subunits. The incorporation of gangliosides into the planar bilayers greatly augmented fusion. Fusion pores developed in four distinct stages after acidification: (a) a pre-pore, electrically quiescent stage; (b) a flickering stage, with 1-2 nS pores opening and closing repetitively; (c) an irreversibly opened stage, in which pore conductances varied between 2 and 100 nS and exhibited diverse kinetics; (d) a fully opened stage, initiated by an instantaneous, time-resolution limited, increase in conductance leveling at approximately 500 nS. The expansion of pores by stages has also been shown to occur during exocytosis in mast cells and fusion of HA-expressing cells and erythrocytes. We conclude that essential features of fusion pores are produced with proteins in just one of the two fusing membranes.
Animals↗
Evaluation of the effect of water-uptake on the impedance of dental resins.
UNLABELLED: Electrical impedance spectroscopy (EIS) offers a quantitative method of measuring the stability of resin films in aqueous solution over time. PURPOSE: The purpose of this study was to measure the EIS of five experimental dental adhesive films (ca. 17 microm thick) of increasing hydrophilicity (ranked by their Hoy's solubility parameters), and how much these values change over 3 weeks in aqueous buffer. METHODS: The resin films were placed in a U-shaped chamber and a pair of Ag-AgCl electrodes was used for EIS. The EIS results were confirmed by immersing the films in 50% AgNO3 for 24 h to trace the distribution of any water absorption into the resins by TEM observations. RESULTS: The resistance (Rr) of the resins 1-4 films increased most during the first day, and varied from 1x10(11) ohm for resin 1, to 40Omega for resin 5 at day 1. The day 1 Rr values of resins 1-4 were inversely proportional to their Hoy's solubility parameter for hydrogen bonding forces. Electrical impedance values of resins 1-3 and 5 varied widely but were relatively constant over time, while those of resin 4 decreased more than 99% from day 1 to 21 (p<0.05). Capacitance (Cr) of films of resins 1-4 all increased over the first day and then were relatively unchanged over the 20 days (except for resin 4 that continued to increase) and were between 0.01 and 1 nF. Silver uptake by TEM revealed the development of water-filled branching structures that formed in resins 4 and 5 over time.
Adhesives↗
Computer simulation of cardiopulmonary resuscitation: computer analysis of a simple electrical model of the circulation.
Extensive research is being conducted to study the mechanism of blood flow during cardiopulmonary resuscitation (CPR). Recently, work has been published using a simple electrical model of the circulation to simulate the hemodynamics of CPR. This analog was a hard-wired circuit consisting of the heart and great vessels modeled as a resistive-capacitive network, pressure as voltage, blood flow as current, blood inertia as inductance and vascular valves as diodes. Such a model is useful for examining the physiology of various methods and techniques of CPR administration. In this investigation, a general purpose circuit simulation program, SPICE Version 2G.6, was used to analyze previously published CPR models. With minor modifications, the program was fully able to simulate the hard-wired circuits. The program is very flexible, allowing for easy model modification and a wide range of parameter values. In addition, the program offers the advantages of increased accuracy and low cost. Suggested future applications are for rapid evaluation of new CPR concepts.
Aorta↗
Heterogeneous expression of the delayed-rectifier K+ currents i(K,r) and i(K,s) in rabbit sinoatrial node cells.
1. The electrical activity of sinoatrial node cells is heterogeneous. To understand the reasons for this, the density of the delayed-rectifier K+ current and its two components, i(K,r) and i(K,s), as a function of the size (as measured by cell capacitance) of rabbit sinoatrial node cells was investigated using the whole-cell voltage-clamp technique at 35 degrees C. 2. i(K,r) and i(K,s) were isolated using E-4031 and 293B. Features of the E-4031-sensitive and 293B-insensitive currents corresponded well to those of i(K,r), while features of the E-4031-insensitive and 293B-sensitive currents corresponded well to those of i(K,s). 3. The densities of the outward current under control conditions and the drug-sensitive and -insensitive currents were significantly (P < 0.01) correlated with cell capacitance, with current densities being greater in larger cells. 4. The effects of partial blockade of i(K,r) by 0.1 microM E-4031 on spontaneous action potentials were greater in smaller cells. 5. It is concluded that there are cell size-dependent differences in the density of the i(K,r) and i(K,s) components, and these may be involved in the heterogeneity of the electrical activity of single sinoatrial node cells as well as that of the intact sinoatrial node.
Action Potentials↗
Action potentials initiated by single channels opening in a small neuron (rat olfactory receptor).
Rat olfactory receptor neurons were enzymatically dissociated and studied with the cell-attached configuration of the patch-clamp technique. Biphasic current waveforms induced across the membrane patch by intracellular action potentials were observed in approximately 5% of cells studied. In one cell in particular, current injected by the opening of a single channel initiated an action potential in the remainder of the cell each time the channel opened. A conventional type of electrical model of the cell and patch allowed the accurate modeling of cell excitability. The same model was used to explain the shape of the action potential current waveforms induced across the patch. The analysis indicated that the whole cell resistance (Ro) was approximately 40 G omega and the membrane capacitance (Co) was close to the standard value of 1 microF.cm-2. In addition, the threshold potential change necessary to initiate an action potential (Vth) was approximately 13 mV and a minimum current injection of 1 pA was required to depolarize the cell to spike threshold. When the smaller size of mammalian receptors are taken into account, membrane electrical properties were found to be consistent with those of salamander cells investigated by others using whole-cell recording. The analysis also revealed possible errors in the determination of single-channel conductances and reversal potentials by cell-attached recording from small cells.
Action Potentials↗
Use of electrochemical impedance measurements to monitor beta-adrenergic stimulation of bovine aortic endothelial cells.
Due to the high permeability of endothelial cell layers derived from macrovascular vessels, precise determination of their barrier function towards ion movement requires refined experimental techniques. We thus cultured bovine aortic endothelial cells (BAEC) directly on thin gold-film electrodes and measured the electrochemical impedance to study their passive electrical properties in general and during beta-adrenergic stimulation. Impedance spectra (10-2.10(6) Hz) of confluent cell monolayers revealed that the electrical characteristics of the cells can be modelled by a simple resistor-capacitor parallel network. Under control conditions the overall resistance of confluent BAEC monolayers was 3.6+/-0.6 Omega.cm2 (n=30) and the capacitance was 0. 6+/-0.1 microF/cm2. Both quantities are discussed with respect to morphological characteristics of these cells. Stimulation of BAECs with the synthetic beta-adrenoceptor agonist isoproterenol leads to a concentration-dependent, highly specific increase of the cell layer resistance characterized by a concentration for half-maximal response (EC50) of 0.3+/-0.1 microM. The cell layer capacitance, however, remained unaffected. Using impedance measurements at a single frequency, we analysed the response of BAECs to treatment with isoproterenol in comparison with several chemically unrelated compounds known to stimulate the adenosine 3',5'-cyclic monophosphate (cAMP)-dependent signal transduction cascade. These studies confirmed that the enhancement of the cell layer resistance after beta-adrenergic stimulation is mediated by an increase in intracellular cAMP.
Adenylyl Cyclases↗
Dielectric behavior of yeast cells treated with HgC-12 and cetyl trimethyl ammonium bromide.
The change in dielectric properties caused by the destruction of the transport barrier of yeast cells has been investigated. Dielectric measurements were made over the frequency range of 1 kc to 2 Mc by using "leaky" yeast cells prepared by treatments with HgCl(2) or CTAB (cetyl trimethyl ammonium bromide). The Hg-treated cells were observed to give smaller dielectric constants and lower critical frequencies as compared with that of the intact cells, while the CTAB-treated cells gave no clear-cut dielectric dispersion. These observations are interpreted on the basis of Maxwell-Wagner's theory as indicating the changes in the intracellular conductivity, the membrane capacitance and the membrane conductance.
Anti-Infective Agents↗
Inward rectifier K+-channel kinetics from analysis of the complex conductance of Aplysia neuronal membrane.
Conduction in inward rectifier, K+-channels in Aplysia neuron and Ba++ blockade of these channels were studied by rapid measurement of the membrane complex admittance in the frequency range 0.05 to 200 Hz during voltage clamps to membrane potentials in the range -90 to -40 mV. Complex ionic conductances of K+ and Cl- rectifiers were extracted from complex admittances of other membrane conduction processes and capacitance by vector subtraction of the membrane complex admittance during suppressed inward K+ current (near zero-mean current and in zero [K+]0) from complex admittances determined at other [K+]0 and membrane potentials. The contribution of the K+ rectifier to the admittance is distinguishable in the frequency domain above 1 Hz from the contribution of the Cl- rectifier, which is only apparent at frequencies less than 0.1 Hz. The voltage dependence (-90 to -40 mV) of the chord conductance (0.2 to 0.05 microS) and the relaxation time (4-8 ms) of K+ rectifier channels at [K+]0 = 40 mM were determined by curve fits of admittance data by a membrane admittance model based on the linearized Hodgkin-Huxley equations. The conductance of inward rectifier, K+ channels at a membrane potential of -80 mV had a square-root dependence on external K+ concentration, and the relaxation time increased from 2 to 7.5 ms for [K+]0 = 20 and 100 mM, respectively. The complex conductance of the inward K+ rectifier, affected by Ba++, was obtained by complex vector subtraction of the membrane admittance during blockage of inward rectifier, K+ channels (at -35 mV and [Ba++]0 = 5 mM) from admittances determined at -80 mV and at other Ba++ concentrations. The relaxation time of the blockade process decreased with increases in Ba++ concentration. An open-closed channel state model produces the inductive-like kinetic behavior in the complex conductance of inward rectifier, K+ channels and the addition of a blocked channel state accounts for the capacitive-like kinetic behavior of the Ba++ blockade process.
Animals↗
Voltage-sensitive outward currents in cat motoneurones.
1. The soma membrane of cat motoneurones was voltage-clamped in vivo using intracellular current and voltage electrodes whose tips were separated by at least 5 micrometer. 2. Depolarization activates two separate, non-interacting K conductance systems whose rates of activation and decay differ by a factor of about 10. These conductances have a similar reversal potential, in the range of -6 to -21 mV (these and all subsequent voltages are expressed relative to the resting potential). Both conductances show linear 'instantaneous' current-voltage relationships. The steady-state magnitudes of both conductances increase with increasing depolarization. Neither conductance inactivates substantially during prolonged depolarizations. 3. The faster K conductance is similar to that described for squid axons and frog node. Activation begins at about +30 mV and is more than 90% complete within 5 msec of a depolarizing voltage step to +50 mV. Activation kinetics appear to be nonlinear. This fast K conductance contributes to the fast falling phase of the action potential. Following repolarization, this conductance decays with a time constant of 2-4 msec. 4. The slower K conductance activates during depolarizations of 10 mV or greater. The activation and decay of this conductance can be described by first-order exponential functions with time constants ranging from 20 to 50 msec. The slow K conductance underlies the prolonged hyperpolarization that follows motoneurone action potentials. Evidence from other studies suggests that this slow K conductance is regulated by intracellular Ca ions. 5. In addition to the two K conductance systems activated by depolarization, motoneurones exhibit another distinct conductance system that is activated by hyperpolarization. This third system has a reversal potential near the resting potential. Activation of this conductance during a hyperpolarizing voltage step can be fitted by a single exponential function with a time constant of 50-60 msec over the range -20 to -50 mV. This hyperpolarization-activated conductance accounts for some aspects of the anomalous rectification reported in cat motoneurones. 6. When the clamp circuit was turned off and the motoneurones were stimulated to discharge repetitively by depolarizing current steps, the apparent soma threshold voltage increased as the applied current (and discharge frequency) increased. 7. The basic features of the motoneurone action potential were reconstructed by simulations based on voltage clamp measurements of the voltage dependent conductance systems and previous measurements of passive membrane properties. These simulations assumed that the kinetics of the fast Na and K conductance systems in motoneurones can be described by equations of the same form as the Hodgkin-Huxley equations. These action potential reconstructions indicated that a major portion of the delayed depolarization following the action potential is attributable to capacitative currents from the dendrites...
Action Potentials↗
Electrophysiological observations in normal and dystrophic chicken muscles.
Intracellular recordings were made on the fast posterior latissimus dorsi muscles of normal and dystrophic chickens. In the dystrophic chickens, the rate of rise of the action potential was decreased. With repetitive indirect stimulation, the action potentials decreased in size and disappeared; only an end-plate potential remained. Membrane resistance, membrane capacitance, and duration of miniature end-plate potentials were increased. A decrease in sodium permeability may be in part responsible for the observed alterations in the electrical properties of the nerve terminal and postsynaptic muscle membrane.
Action Potentials↗
Thermo- and photoelectric current in hornet cuticle.
Thermoelectric and photoelectric currents were measured in the cuticle of hornets. The spontaneous current in the studied specimens ranged between 30-40 nAmp under conditions of darkness whereas under illumination the current drops to near zero. Upon warming up to 28-29 degrees C, the current rises to 50-200 nAmp but subsequently, after a while, it declines, regardless of whether the temperature is held steady, continues to rise or is lowered. In light, the current values are lower than in darkness and this under all conditions. When the specimen is charged with an electric current under fixed temperature, the current attains several microAmp in darkness but is usually less than that under illumination by about one order of magnitude. The capacitance values range between 1-7 mFarad both in light and in the dark. Possible mechanisms for creating this cuticular current and the changes which it undergoes under the various experimental conditions are discussed, and so also the properties of hornet cuticle as a semiconductor and possible applications of the described phenomena in everyday life of hornets.
Animals↗
Analogue solution for electrical capacity of membrane-covered cubes in cubic array at high concentration.
Earlier measurements have shown that the equations derived for the resistance of suspension of spheres apply up to a volume concentration of 100% for close-packing forms. They have also shown, by a resistance-capacitance analogue, that they apply for the capacity of a close-packing of membrane-covered square cylinders in square array, approximating muscle and nerve. The present work is an extension of the two-dimensional to a three-dimensional array of membrane-covered cubes in a cubic array. It is found by measurements of a three-dimensional electrolytic analogue that the capacitance is indeed expressed by an extension of the analytic solution at low concentrations up to 100% volume concentration of the membrane-covered form, such as epithelial tissues. There is thus at least one example each of two-and three-dimensional forms which conform to the low concentration analysis up to 100% volume and so give a basis for the extensions to other and more complicated forms to complete a survey to work begun by Fricke in 1923.
Cell Physiological Phenomena↗
Properties of the fusion pore that forms during exocytosis of a mast cell secretory vesicle.
During exocytosis, secretory vesicles of mast cells generate a current transient that marks the opening of the fusion pore, the first aqueous connection that forms between the vesicle lumen and the cell exterior. By recording and analyzing such current transients, we have tracked the conductance of the fusion pore over the first millisecond of its existence. The first opening of the pore occurs rapidly, generally within 100 microseconds at 23 degrees C. The electric conductance of the pore is a few hundred picosiemens at first, but gradually increases over the subsequent milliseconds. Evidently the pore opens abruptly and then dilates. The initial conductance of the pore suggests a diameter comparable to that of a large ion channel. From an analysis of "capacitance flicker" we infer that a pore can increase its diameter severalfold and still close again completely. This suggests that several early events in membrane fusion are reversible.
Animals↗
Reliability of spike propagation in arborizations of dorsal root fibers studied by analysis of postsynaptic potentials mediated by electrotonic coupling in the frog spinal cord.
1. Postsynaptic potentials were recorded in lumbar motoneurons of the frog in response to electrical activation of dorsal roots. After chemical synaptic transmission was blocked by replacing Ca2+ with Mg2+ in the superfusion medium, it was confirmed that the remaining electrical excitatory postsynaptic potentials (EEPSPs) recorded in motoneurons consisted of potential changes-produced by electrical coupling between the motoneurons and the stimulated axons. The EEPSPs could then be used as an assay to study the reliability of spike propagation into presynaptic terminals. 2. EEPSPs typically consisted of three components. The first was a small positive deflection (prespike or presynaptic volley) that could also be recorded extracellularly. The second component was a spikelike fast positive component and the third was a slow positive component that followed the second but had a distinct maximum and a slow decay. The amplitude of the fast component did not correlate with that of either the prespike or the slow component. 3. 4-Aminopyridine (0.1 mM), which widens action potentials by blocking K+ channels, increased the amplitude and width of EEPSPs. Heptanol (1-4 mM), which is known to be a blocker of electrical coupling, could block EEPSPs. 4. The amplitudes of EEPSPs evoked by dorsal root stimulation were compared at different temperatures (7.5-19.5 degrees C). A slight decrease of the amplitude of the fast component with increasing temperature (Q10 = 0.8) was within limits predicted by resistance-capacitance filtering of the presynaptic spike at the different temperatures, suggesting that the temperature does not affect propagation of the spike in this synapse. 5. The amplitude of the fast component of EEPSPs evoked by single-pulse and paired-pulse stimulation did not fluctuate more than the baseline noise in 37 experiments in which the SD of baseline noise was < 100 microV. We conclude that electrical synaptic transmission does not fluctuate intermittently in this system, and that branch points conduct or fail to conduct for periods of time longer than the longest period in the analyzed experiments.
Animals↗
Secretory apical Cl- channels in A6 cells: possible control by cell Ca2+ and cAMP.
Distal kidney cells (A6) from Xenopus laevis were cultured to confluency on porous supports. Tissues were mounted in Ussing-type chambers to measure short-circuit current (Isc), transepithelial conductance and capacitance, and to analyse the fluctuation in Isc. In the absence of apical NaCl, but with normal basolateral NaCl Ringer's solution, extracellular addition of ATP, oxytocin, a membrane-permeant cAMP derivative, and forskolin produced a transient increase of the electrical parameters. Noise analysis revealed a spontaneous Lorentzian component. All responses depend strictly on the presence of basolateral Cl- and are caused by the activation of an apical (CFTR type) Cl- permeability. Repetitive treatment with ATP (or oxytocin) resulted in refractoriness. ATP and oxytocin acted antagonistically, whereas cAMP and ATP had additive effects. Incubation with the vesicular Ca2+ pump inhibitor thapsigargin or application of the Ca2+ channel blocker nifedipine elicited finite but variable Cl- channel activity. After treatment with nifedipine or thapsigargin, the response to oxytocin was severely impaired. We speculate that not only cAMP but also cell Ca2+ plays a crucial role in the activation of CFTR in A6. Ca2+ may be multifunctional but the rise in capacitance (apical area) observed with all stimulants strongly suggests its involvement in, and contribution to, exocytosis in the process of the CFTR-mediated transcellular Cl- movements.
Adenosine Triphosphate↗
Electrical properties associated with wide intercellular clefts in rabbit Purkinje fibres.
1. Rabbit Purkinje fibres were studied using micro-electrode recordings of electrical activity or a two-micro-electrode voltage clamp. Previous morphological work had suggested that these preparations offer structural advantages for the analysis of ionic permeability mechanisms. 2. Viable preparations could be obtained consistently by exposure to a K glutamate Tyrode solution during excision and recovery. In NaCl Tyrode solution, the action potential showed a large overshoot and fully developed plateau, but no pacemaker depolarization at negative potentials. 3. The passive electrical properties were consistent with morphological evidence for the accessibility of cleft membranes within the cell bundle. Electrotonic responses to intracellular current steps showed the behaviour expected for a simple leaky capacitative cable. Capacitative current transients under voltage clamp were changed very little by an eightfold reduction in the external solution conductivity. 4. Slow current changes attributable to K depletion were small compared to those found in other cardiac preparations. The amount of depletion was close to that predicted by a cleft model which assumed free K diffusion in 1 micron clefts. 5. Step depolarizations over the plateau range of potentials evoked a slow inward current which was resistant to tetrodotoxin but blocked by D600. 6. Strong depolarizations to potentials near 0 mV elicited a transient outward current and a slowly activating late outward current. Both components resembled currents found in sheep or calf Purkinje fibres. 7. These experiments support previous interpretations of slow plateau currents in terms of genuine permeability changes. The rabbit Purkinje fibre may allow various ionic channels to be studied with relatively little interference from radial non-uniformities in membrane potential or ion concentration.
Action Potentials↗