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PubMed2004

Store-operated calcium entry: a tough nut to CRAC.

Store-operated or capacitative Ca2+ entry is a prominent feature of many electrically nonexcitable cell types. It is due to Ca2+ ion permeation pathways in the plasma membrane that are activated after receptor-mediated Ca2+ release from intracellular stores. Despite hundreds of publications on the topic of store-operated Ca2+ entry and intense efforts by many dedicated laboratories, neither the molecular nature of the ion permeation pathway nor its activation mechanism is known. Here we review the progress made on the characterization of store-operated currents and the challenges encountered in identifying the molecular components of store-operated Ca2+ entry.

Animals↗
PubMed1999

Active electrolocation of objects in weakly electric fish

Weakly electric fish produce electric signals (electric organ discharges, EODs) with a specialised electric organ creating an electric field around their body. Objects within this field alter the EOD-induced current at epidermal electroreceptor organs, which are distributed over almost the entire body surface. The detection, localisation and analysis of objects performed by monitoring self-produced electric signals is called active electrolocation. Electric fish employ active electrolocation to detect objects that are less than 12 cm away and have electric properties that are different from those of the surrounding water. Within this range, the mormyrid Gnathonemus petersii can also perceive the distance of objects. Depth perception is independent of object parameters such as size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters of the electric image that the object projects onto the fish's skin. Electric fish can not only locate objects but can also analyse their electrical properties. Fish are informed about object impedance by measuring local amplitude changes at their receptor organs evoked by an object. In addition, all electric fish studied so far can independently determine the capacitative and resistive components of objects that possess complex impedances. This ability allows the fish to discriminate between living and non-living matter, because capacitance is a property of living organisms. African mormyrids and South American gymnotiforms use different mechanisms for capacitance detection. Mormyrids detect capacitance-evoked EOD waveform distortions, whereas gymnotiforms perform time measurements. Gymnotiforms measure the temporal phase shift of their EODs induced at body parts close to the object relative to unaffected body parts further away.

Journal Article↗
PubMed2002

X-ray absolute calibration of the time response of a silicon photodiode.

The time-dependent response of a 1-mm2 silicon photodiode was characterized by use of pulsed synchrotron radiation in the 4- to 16-nm-wavelength range. Modeling the input radiation pulse and the electrical response of the photodiode allowed the photodiode's capacitance as a function of wavelength and applied bias voltage to be determined. The capacitance was in the 7- to 19-pF range and resulted in response fall times as small as 0.4 ns. The capacitance determined by pulsed x-ray illumination was in good agreement with the capacitance determined by pulsed optical laser illumination. The absolute responsivity was measured by comparison with the responsivity of a calibrated photodiode.

Journal Article↗
PubMed2001

Signal transduction in electrically stimulated bone cells.

BACKGROUND: Electrical stimulation is used to treat nonunions and to augment spinal fusions. We studied the biochemical pathways that are activated in signal transduction when various types of electrical stimulation are applied to bone cells. METHODS: Cultured MC3T3-E1 bone cells were exposed to capacitive coupling, inductive coupling, or combined electromagnetic fields at appropriate field strengths for thirty minutes and for two, six, and twenty-four hours. The DNA content of each dish was determined. Other cultures of MC3T3-E1 bone cells were exposed to capacitive coupling, inductive coupling, or combined electromagnetic fields for two hours in the presence of various inhibitors of signal transduction, with or without electrical stimulation, and the DNA content of each dish was determined. RESULTS: All three signals produced a significant increase in DNA content per dish compared with that in the controls at all time-points (p < 0.05), but only exposure to capacitive coupling resulted in a significant, ever-increasing DNA production at each time-period beyond thirty minutes. The use of specific metabolic inhibitors indicated that, with capacitive coupling, signal transduction was by means of influx of Ca(2+) through voltage-gated calcium channels leading to an increase in cytosolic Ca(2+) (blocked by verapamil), cytoskeletal calmodulin (blocked by W-7), and prostaglandin E2 (blocked by indomethacin). With inductive coupling and combined electromagnetic fields, signal transduction was by means of intracellular release of Ca(2+) leading to an increase in cytosolic Ca(2+) (blocked by TMB-8) and an increase in activated cytoskeletal calmodulin (blocked by W-7). CONCLUSIONS: The initial events in signal transduction were found to be different when capacitive coupling was compared with inductive coupling and with combined electromagnetic fields; the initial event with capacitive coupling is Ca(2+) ion translocation through cell-membrane voltage-gated calcium channels, whereas the initial event with inductive coupling and with combined electromagnetic fields is the release of Ca(2+) from intracellular stores. The final pathway, however, is the same for all three signals-that is, there is an increase in cytosolic Ca(2+) and an increase in activated cytoskeletal calmodulin.

Animals↗
PubMed1983

Formation and properties of cell-size lipid bilayer vesicles.

Hydration of single or mixed phospholipids or lipid protein mixtures at low ionic strength results in the formation of a population of large, solvent free, single bilayer vesicles with included volumes of up to 300 microliters/mumol lipid. Their size ranges from 0.1 to 300 microns and they can be sorted out according to size by centrifugation. When formed in distilled water their internal solution has a conductivity of 20-50 microseconds/cm-1, an osmolarity of 0.5-5 mOsM, and a density of 1.0005-1.001. The osmotic pressure produced by the internal solutes cause a surface stress of 25 dyn/cm for a 20-microns vesicle. Their elastic constant ranges from 75-150 dyn/cm. During formation they can internalize particles such as latex beads or cell nuclei. They can be impaled with microelectrodes, or patch clamped. They can also be sealed to a small Vaseline-treated hole in a thin partition between two aqueous compartments. Sealing occurs in two stages. In the first stage sealing resistance is similar to that seen with patch-clamp pipettes. In the second stage, a much tighter seal is obtained. After sealing, the smaller portion of the sealed vesicle can be selectively broken by an electric shock leaving a single membrane across the hole. The capacitance and resistance of such membranes, in the presence of 10 mM NaCl, are approximately 0.7 microF/cm2 and 10(8) omega cm2 for pure lipid vesicles. Gramicidin increases the membrane conductance and monazomycin induces voltage-dependent gating thus providing further evidence that the vesicles are bounded by a single bilayer.

Animals↗
PubMed1987

Reflex control of nasal blood vessels.

The effect of stimulation of vagal afferent fibers on nasal blood vessels was studied in 36 cats. Volume change of the nasal capacitance vessels was measured by plethysmographic balloons inserted into the nose. Electrical stimulation of the vagus nerve produced a vasodilatation of nasal mucosa. Pulmonary stretch receptor stimulation by veratridine alkaloid and progressive lung inflation in open-chest cats also produced a vasodilatation of the nasal mucosa. These reflexes were abolished by sectioning the vagus nerves. These results suggest a reflex arc between the lung and nasal capacitance vessels which arises from pulmonary stretch receptors.

Airway Resistance↗
PubMed1980

II. Electrical measurements in the nanosecond range of the charge separation from chloroplasts spread at a heptane-water interface. Application of a novel capacitive electrode.

Spinach chloroplasts are spread at a heptane-water interface. Applying a novel capacitative electrode introduced in the preceding paper (Trissl, H.-W. (1980) Biochim. Biophys. Acta 595, 82-95) the changes of the interface potential induced by single laser flashes are investigated. The following results are obtained: (1) The chloroplasts spread at the interface form a thin layer with asymmetrical orientation. The structural state of this layer is discussed. (2) The photovoltage from the interfacial layer shows similar characteristics as the field-indicating absorption change of chloroplast suspensions, the latter reflecting the photosynthetic primary charge separation: (a) Both can be abolished by addition of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea. (b) About one half of the signals can be reactivated by addition of N-methyl-phenazonium methosulfate. (c) Both signals saturate at low flash light intensities. (d) Both signals can be abolished by background illumination of comparable intensities. (e) Both signals are independent of the ionic strength. (3) The half-rise time of the photovoltage is determined to be less than 3 ns. It is suggested from these results that the photovoltage from the interfacial layer reflects the primary charge separation process in photosynthesis, i.e. the latter is accomplished also within less than 3 ns.

Chloroplasts↗
PubMed1985

Capacitive and ionic currents in BLM from phosphatidic acid in Ca2+-induced phase transition.

The development of electric current with time in a bilayer lipid membrane (BLM) formed from dipalmitoylphosphatidic acid on introducing Ca2+ ions into the medium was studied at constant temperature and pH. The phase transition in the Ca2+-induced BLM is accompanied by the initial capacitive current followed by the occurrence of single ionic channels. The amount of transported charges in the capacitive current is 5 C/ microF. The conductivity of the single ionic channels ranges from 50 to 100 pSm.

Calcium↗
PubMed1994

Cell coupling in the supporting cells of Corti's organ: sensitivity to intracellular H+ and Ca+2.

The input capacitance of cell pairs or small groups can be used to gauge the degree of electrical coupling via gap junctions (Santos-Sacchi, 1991). In order to estimate junctional sensitivity to intracellular Ca+2 and H+ concentration, the input capacitance of supporting cell syncytia of the organ of Corti was measured with the whole cell voltage clamp technique, while directly modifying the cation concentrations via the patch pipette. Typically, a pH below 6.5 was capable of uncoupling Hensen cells. On the other hand, pCa levels as low as 3 were ineffective.

Animals↗
PubMed1993

A simplified method for selecting a carbon-fiber electrode in pulse voltammetry.

A method for selecting a usable carbon-fiber electrode using the equivalent resistance and capacitance is presented. This method uses an instrument with a PC-based look-up table for measuring the electrical characteristics of a carbon-fiber electrode in pulse voltammetry. Using this instrument, the equivalent resistance and capacitance of the carbon-fiber electrode in saturated sodium chloride solution can be obtained. This instrument includes a decade resistance box, a peak current detection and hold circuit, a half peak comparator and a decay duration counter. A look-up table is established by using RC circuits to emulate the electrochemical reaction of the carbon-fiber electrode in pulse voltammetry. The equivalent resistance is obtained from the decade resistance box according to Kirchhoff's law. Then the equivalent capacitance is determined from the decay duration counter reading and equivalent resistance with the look-up table via a PC interpolation program. After obtaining the equivalent resistance and capacitance of an electrode, the values are compared with the usable thresholds. This method provides an effective quality evaluation index of carbon-fiber electrode for the user in order to reduce electrode-induced experimental failure. The method is also available for other kinds of carbon-fiber electrodes as long as their look-up table and desired thresholds are established.

Electric Conductivity↗
PubMed1984

A sequential pulse generator for producing true biphasic stimuli.

The ability to generate biphasic pulses during electrical stimulation of nervous tissue has important advantages over monophasic or capacitively coupled stimulation. A comparatively simple circuit is described which, when used with standard electrophysiological laboratory equipment, can economically implement biphasic stimulation. The resultant system is quite flexible, yet easy to operate.

Electric Stimulation↗
PubMed1989

[The effect of the ventral structures of the medulla oblongata on systemic arterial pressure and on the resistance and capacitance of the skeletal muscle vessels].

Following the isolation of ventral portions of the medulla oblongata from the dorsal ones and from the upper parts of the c. n. s. in cats, no changes were found in the initial level of systemic blood pressure, in perfusion pressure or in venous outflow in the m. gastrocnemius, vessels. Electrical stimulation of ventral portions of the lateral paragigantocellular nucleus under these conditions increased the systemic AP, regional vascular resistance and decreased the capacitance of the n. gastrocnemius' vessels, whereas after bilateral electrical coagulation of the nucleus the stimulation led to a stable and obvious decrease in the systemic AP and perfusion pressure in the muscle vessels. No changes of the regional vascular capacitance were noted. The significance of ventral structures of medulla oblongata in maintaining of initial AP level, formation of tonic neurogenic messages to arterial vessels of m. gastrocnemius and in actualization of the reflex neurogenic effects upon arterial and venous vessels of skeletal muscles, is discussed.

Animals↗
PubMed1997

Functional coupling in bovine ciliary epithelial cells is modulated by carbachol.

The functional coupling of the ciliary epithelium was studied in isolated pairs (couplets) of pigmented ciliary epithelial (PCE) and nonpigmented ciliary epithelial (NPCE) cells using the whole cell patch clamp and the fluorescent dye lucifer yellow. One cell of the pair (usually the NPCE cell of a NPCE-PCE cell couplet) was accessed with a 2-5 M omega electrode, containing 1-2 mM lucifer yellow, in the whole cell configuration of the patch clamp. After voltage-clamp experiments were completed, cells were viewed under a fluorescent microscope to confirm that the cells were coupled. The electrical coupling of the cells was also studied by calculating the capacitance (using the time-domain technique), assuming a "supercell" model for coupled cells. The mean capacitance of coupled pairs was 79.8 +/- 4.3 (SE) pF (n = 47) compared with single cell capacitances of 36.8 +/- 3.4 pF (n = 10) for PCE cells and 38.1 +/- 3.1 pF (n = 15) for NPCE cells. Octanol, carbachol (CCh), and raised extracellular Ca2+ concentration ([Ca2+]o) all caused uncoupling in pairs (couplets) of coupled NPCE and PCE cells. At room temperature (22-24 degrees C), the capacitance of the couplets decreased from 70.5 +/- 8.0 to 48.0 +/- 5.2 pF (n = 5) when exposed to octanol (1 mM), from 73.8 +/- 9.2 to 43.2 +/- 9.5 pF (n = 4) when exposed to CCh (100 microM), and from 80.5 +/- 6.7 to 49.9 +/- 7.8 pF (n = 4) when exposed to 10 mM [Ca2+]o. The response to CCh was dose dependent; at higher temperatures of 34-37 degrees C, 10 microM CCh caused a 38% reduction in capacitance, from 53.7 +/- 9.7 to 33.5 +/- 3.3 pF (n = 7) with a half-time of 249 s, and 100 microM CCh caused a 49% reduction in capacitance, from 51.3 +/- 5.6 to 26.0 +/- 2.4 pF (n = 7) with a half-time of 124 s. After pairs uncoupled and the uncoupling agent was washed out, the cell pairs often exhibited an increase in capacitance that we interpreted as "recoupling" or a reopening of the gap junctional communication pathway; the half-time for this process was 729 s after uncoupling with 100 microM CCh and 211 s after uncoupling with 10 microM CCh. This interpretation was confirmed optically by the spread of lucifer yellow into both cells of an uncoupled pair with a time course corresponding to the increase in electrical coupling. The controllable coupling of ciliary epithelial cells extends the idea of a functional syncytium involved in active transport. PCE cells take up solute and water from the blood, which then cross to NPCE cells via gap junctions and from there are secreted into the posterior chamber of the eye. Modulation of the coupling between NPCE and PCE cells may provide a mechanism to control secretion.

Animals↗
PubMed1993

Characterization of the preparation process and the photochemical control of electrical properties of bilayer lipid membranes containing azobenzene chromophores.

We prepared photoresponsive bilayer lipid membranes (BLMs) containing azobenzene derivatives (4'-octylazobenzene-4-oxybutyric acid (AZ)) and observed the rapid and reversible changes in their electrical properties when irradiated with light. The BLMs consist of AZ (8 mol%) and glyceryl monooleate. The changes in capacitance and conductance upon irradiation by light were found to be 10 and 20%, respectively. The changes in the electrical properties of the membrane and in the structure of AZ under light irradiation were analyzed simultaneously by in-situ spectroscopic, electrical and microscopic measurements. These measurements showed that the electrical changes induced by exposure to light resulted from reversible changes in the membrane structure initiated by the photoisomerization reaction of AZ. This structural change in the membrane occurred within 1 s.

Azo Compounds↗
PubMed1992

Electrical energy changes conductivity and determines optimal electrotransformation frequency in gram-negative bacteria.

In many bacterial electrotransformation protocols, pulse time is related to the time constant for a capacitor discharging across a sample of fixed resistance. Using an electroporator which controls pulse time independently of the capacitor time constant, we found that the resistance of bacterial suspensions fluctuates widely during capacitor discharge. With three gram-negative species of bacteria, electrotransformation frequency and survival could be more simply related to the electrical energy delivered in each pulse than to component parameters, such as initial field strength, capacitance, and pulse time. In each case, the number of transformants per survivor increased exponentially and leveled off when more than 0.5 to 1.0 J of electrical energy was delivered. An inverse log-linear relationship between survival and energy delivered was also observed for all three species.

Journal Article↗
PubMedDate not supplied

The electrical and spectroscopic properties of planar asymmetrical membranes incorporating chlorophyll a and plastoquinone-9. Influence of surface charges on electron transfer.

We studied the influence of surface charges on the efficiencies of electron transfer between a donor molecule, chlorophyll a (Chla), and an acceptor molecule, plastoquinone-9 (PQ-9), asymmetrically incorporated into a phospholipid matrix built from phosphatidylethanolamine, phosphatidylserine, and dimethyldistearylammonium bromide. Membrane conductance and capacitance measurements, as well as fluorescence emission experiments, were performed on bilayers containing positive or negative surface charges. The conductance of the bilayers showed important increases upon illumination of the Chla, this effect being observed only when both the donor and the acceptor molecules were present within the bilayer. This suggested that an electron transfer between Chla and PQ-9 occurred. The same kind of behaviour was observed with the membrane capacitance, but the amplitude of the effect was smaller. The results showed that an electric field gradient favorably oriented to promote electron transfer from Chla to PQ-9 maximized the electron transfer between these two molecules. However, both the membrane resistance and capacitance were permanently modified when illumination was stopped. On the other hand, the fluorescence results showed that for the range of surface charges covered, the position of the maximum of absorption was found unchanged around 675 nm and the intensity of fluorescence was almost constant, of the order of 7 x 10(6)-8 x 10(6) photons.s-1. This suggested that Chla was embedded as microdomains within the bilayer. The results presented here were also compared with what is known on the organization of the donor and acceptor molecules within the reaction centres of photosynthetic bacteria.

Chlorophyll↗