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PubMed1988

Genetic transformation of Streptococcus thermophilus by electroporation.

A rapid and convenient electroporation procedure was developed for the genetic transformation of intact cells of Streptococcus thermophilus with various species of plasmid DNA. Transformation frequency was influenced by the capacitance and voltage selected for electric pulsing, the pH and composition of the electroporation medium and the molecular mass of the transforming DNA. Electroporation is a simple and effective technique to introduce plasmid DNA into S. thermophilus and useful in the development of recombinant DNA technology for this important industrial microorganism.

Buffers↗
PubMed2005

Kinetic evidences of the existence of positively charged species at the quartz-aqueous solution interface.

To probe the surface speciation of quartz in strong acidic solutions (pH 0-3), where surface titration and electrophoresis are extremely difficult to perform, dissolution rates of this mineral were measured at 25 degrees C and constant ionic strength (1.0 M) using mixed-flow and batch reactors. Dissolution rates increase with activity of protons at 0 < or = pH < or = 3, which suggests the adsorption of H+ on the mineral surface, leading to polarization of SiO bonds and detachment of the silicon atom from the structure. This scheme is consistent with the presence of a non-negligible amount (i.e., up to 30-50% at pH close to 0) of protonated >SiOH2+ species on the surface, as was recently demonstrated using X-ray photoelectron spectroscopy (XPS) analysis of exactly the same quartz sample [Y. Duval, J. Mielczarski, O.S. Pokrovsky, E. Mielczarski, J.J. Ehrhardt, J. Phys. Chem. B 106 (2002) 2937-2945]. A 2-pK electrical double layer (EDL) constant capacitance surface speciation model has been used to model the obtained kinetic data. A set of surface stability constants consistent with previous spectroscopic XPS measurements (pK1 = -1.0 and pK2 = 4.0) and EDL capacitance of 1.5 F/m2 provide adequate description of the dissolution rate with reaction order with respect to [>SiOH2(+)] close to 1. Although the CCM model used in this study presents some limitations on surface charge versus pH dependences, the developed kinetic approach opens new possibilities of probing the surface speciation at the SiO2-aqueous solution interface under extreme solution conditions.

Journal Article↗
PubMed1979

Further development of a model for electrical transmission between myocardial cells not connected by low-resistance pathways.

We previously described a model for the electrical transfer of excitation from one cell to the next which utilized the electric field generated in the cleft between the cells. This model was analyzed only for the steady-state condition. In the present paper, we calculate the effects of membrane capacitance on the transmission of an action potential between two adjacent cardiac cells; the junction between cells was composed of two high-resistance excitable membranes separated by a narrow cleft. The parameters varied for this study included the threshold potential and capacitance of the junctional membranes. The calculations indicate that it is somewhat easier to achieve transmission when capacitive effects are included. Thus, the electric field model provides an alternative means of cell-to-cell propagation between myocardial cells which is electrical in nature but does not require the presence of low-resistance connections between cells.

Action Potentials↗
PubMed2005

Dielectrophoretic force microscopy of aqueous interfaces.

A novel scanning probe microscopy technique has allowed dielectrophoretic force imaging with nanoscale spatial resolution. Dielectrophoresis (DEP) traditionally describes the mobility of polarizable particles in inhomogeneous alternating current (ac) electric fields. Integrating DEP with atomic force microscopy allows for noncontact imaging with the image contrast related to the local electric polarizability. By tuning the ac frequency, dielectric spectroscopy can be performed at solid/liquid interfaces with high spatial resolution. In studies of cells, the frequency-dependent dielectrophoretic force is sensitive to biologically relevant electrical properties, including local membrane capacitance and ion mobility. Consequently, dielectrophoretic force microscopy is well suited for in vitro noncontact scanning probe microscopy of biological systems.

Journal Article↗
PubMed2005

Enhanced anion electroadsorption into carbon molecular sieve electrodes in acidic media.

We previously showed that, for neutral electrolytes of small cations and relatively larger anions, it is possible to design certain pore sizes in active carbons that are large enough to electroadsorb cations but too small to allow anion electroadsorption. This situation leads to an electrical double-layer (EDL) capacitance that is significant only at potentials that are negative to the potential of zero charge (PZC); hence, much smaller capacitance is measured at potentials positive to the PZC. It was found that when the electrolyte is a strong acid (e.g., H(2)SO(4), HCl), a considerable capacitance is observed at positive potentials, even when the average pore size is too small to allow the insertion of large anions in neutral electrolyte solutions. This effect disappears when the pore size becomes considerably larger than the size of the ions. In this case, the EDL capacitance at positive potentials for both neutral and acidic solutions is comparable. The following four-step mechanism was found to comply best with the experimental data: (1) By acid catalysis, the protons form carbonium species within the conjugated carbon network. (2) The anions react with the carbonium ions, providing uncharged species in an activated state, which are chemibound as surface groups to the walls of the pores. (3) Because these surface groups are effectively much smaller in size than are the charged ions, they can migrate by chemical bond exchange within the carbon skeleton via constrictions (known to exist in microporous and molecular sieving carbons), which are too narrow to accommodate hydrated charged species. (4) Upon reaching wider spaces, the uncharged species are reionized and solvated by water molecules, which can fill small pores. The justification for the above mechanism is thoroughly discussed and demonstrated by the experimental results.

Journal Article↗
PubMed1992

Pulmonary capillary pressure: a review.

OBJECTIVES: To demonstrate the importance of a) measuring effective pulmonary capillary pressure and b) evaluating the longitudinal distribution of pulmonary vascular resistance relative to pre- and postcapillary resistances. To review the development of methods used to determine pulmonary capillary pressure in experimental animal and clinical studies. DATA SOURCES: Human, animal, and modeling studies published since 1966 identified through MEDLINE and a review of bibliographies of relevant articles. STUDY SELECTION AND DATA EXTRACTION: All studies identified were reviewed with an emphasis on recent studies and those studies identifying various methodologies used to determine capillary pressure. Experimental studies were selected for their historical value and applicability to the clinical setting. DATA SYNTHESIS: Different models of the pulmonary circulation have been proposed. The electrical circuit model, which incorporated capacitance elements and two or four resistive elements, has been the basis for the determination of pulmonary capillary pressure in isolated lungs and in situ lungs in animals and patients. Methods used to determine pulmonary capillary pressure from a pulmonary arterial pressure tracing after balloon occlusion are: a) division of waveform into two components and logarithmic extrapolation of the slow component to occlusion time; b) visual determination of the pressure inflection point of the pulmonary arterial pressure tracing; and c) computer processing of the total arterial pressure transient. Both ease of calculations and difficulties can arise when each method is used. CONCLUSIONS: Pulmonary capillary hydrostatic pressure is an important determinant of pulmonary edema especially in the setting of pulmonary hypertension and adult respiratory distress syndrome. Hypoxia, sepsis, cardiac valvular disease, and inflammatory mediators produce variable changes in the longitudinal distribution of pulmonary vascular resistance so that an increased capillary pressure cannot be predicted by the pulmonary arterial or occlusion pressure. For proper therapy aimed at decreasing pulmonary vascular resistance, it is important to determine whether or not the particular therapy increases capillary pressure. Pulmonary capillary pressure is the most important determinant of lung fluid balance and is the major physiologic parameter that should be measured when various forms of plasma volume expansion and pulmonary vasodilators are used in the critically ill patient.

Animals↗
PubMed2004

Modeling of charge switching in ferroelectric capacitors.

To simulate charge switching in ferroelectric capacitors, a pair of exponential growth and decay currents is mapped to the process of polarization reversal. This is based on the fact that these exponential currents [i.e., i = I(m) e(t/tau) (t < or = 0) and i = I(m) e(-t/tau) (t > or = 0)], are completely specified by two constants I(m) and tau and each accommodates an integral charge Q = I(m) x tau. Equating this charge to the remanent spontaneous polarization allows for the modeling of switching current. For practical circuit simulations for charge switching, this modeling of switching current is simplified to an exponential decay current whose integral charge is set equal to the total reversed spontaneous polarization. This is because an exponential decay current can be conveniently implemented by charging a series resistor and capacitor (RC) circuit with a pulse-voltage source. The voltage transitions of the pulse source are associated with the polarization reversal and can be controlled with a noninverting Schmitt trigger that toggles at the positive and negative coercive voltages of a ferroelectric capacitor. The final circuit model incorporates such electrical and geometrical parameters as capacitance, remanent spontaneous polarization, coercive field, electrode area, and film thickness of a ferroelectric, thin-film capacitor.

Journal Article↗
PubMed1999

Pharmacological evidence for a KATP channel in renin-secreting cells from rat kidney.

1. Openers of the ATP-sensitive potassium channel (KATP channel) increase and blockers decrease renin secretion. Here we report the effects of levcromakalim (LCRK, a channel opener) and glibenclamide (GBC, a blocker) on membrane potential, whole-cell current and the cytoplasmic Ca2+ concentration of renin-secreting cells (RSC). Studies were performed on afferent arterioles from the kidney of Na+-depleted rats. 2. As monitored with the fluorescent oxonol dye DiBAC4(3), LCRK (0.3 and 1 microM) induced a hyperpolarization of approximately 15 mV which was abolished by GBC (1 microM). 3. Whole-cell current-clamp experiments showed that RSC had a membrane potential of -61 +/- 1 mV (n = 16). LCRK (1 microM) induced a hyperpolarization of 9.9 +/- 0.2 mV (n = 16) which, in the majority of cells, decreased slowly with time. 4. Capacitance measurements showed a strong electrical coupling of the cells in the preparation. 5. At -60 mV, LCRK induced a hyperpolarizing current in a concentration-dependent manner with an EC50 of 152 +/- 31 nM and a maximum current of about 200 pA. 6. Application of GBC (1 microM) produced no effect; however, when applied after LCRK (300 nM), GBC inhibited the opener-induced hyperpolarizing current with an IC50 of 103 +/- 36 nM. 7. LCRK (0.3 and 1 microM) did not significantly affect the cytoplasmic Ca2+ concentration either at rest or after stimulation by angiotensin II. 8. The data show that LCRK induces a GBC-sensitive hyperpolarizing current in rat RSC. This current presumably originates from the activation of KATP channels which pharmacologically resemble those in vascular smooth muscle cells. The stimulatory effect of KATP channel opening on renin secretion is not mediated by a decrease in intracellular Ca2+ concentration.

Angiotensin II↗
PubMed2003

Differential control of adrenal and sympathetic catecholamine release by alpha 2-adrenoceptor subtypes.

In the adrenergic system, release of the neurotransmitter norepinephrine from sympathetic nerves is regulated by presynaptic inhibitory alpha2-adrenoceptors, but it is unknown whether release of epinephrine from the adrenal gland is controlled by a similar short feedback loop. Using gene-targeted mice we demonstrate that two distinct subtypes of alpha2-adrenoceptors control release of catecholamines from sympathetic nerves (alpha 2A) and from the adrenal medulla (alpha 2C). In isolated mouse chromaffin cells, alpha2-receptor activation inhibited the electrically stimulated increase in cell capacitance (a correlate of exocytosis), voltage-activated Ca2+ current, as well as secretion of epinephrine and norepinephrine. The inhibitory effects of alpha2-agonists on cell capacitance, voltage-activated Ca2+ currents, and on catecholamine secretion were completely abolished in chromaffin cells isolated from alpha 2C-receptor-deficient mice. In vivo, deletion of sympathetic or adrenal feedback control led to increased plasma and urine norepinephrine (alpha 2A-knockout) and epinephrine levels (alpha 2C-knockout), respectively. Loss of feedback inhibition was compensated by increased tyrosine hydroxylase activity, as detected by elevated tissue dihydroxyphenylalanine levels. Thus, receptor subtype diversity in the adrenergic system has emerged to selectively control sympathetic and adrenal catecholamine secretion via distinct alpha2-adrenoceptor subtypes. Short-loop feedback inhibition of epinephrine release from the adrenal gland may represent a novel therapeutic target for diseases that arise from enhanced adrenergic stimulation.

Adrenal Glands↗
PubMed2001

Interaction between lipopolysaccharide (LPS), LPS-binding protein (LBP), and planar membranes.

The mechanism of interaction of the lipopolysaccharide (LPS)-binding protein, LBP, with differently composed symmetric and asymmetric planar lipid bilayers was investigated in electrical measurements (membrane current, potential, capacitance). From a change of the inner membrane potential difference, binding of LBP to membranes was deduced. After addition of LBP to one side of the membrane, binding of anti-LBP antibodies and LPS to LBP on both sides of the bilayer was observed. Effects resulting from an interaction of anti-LBP antiserum with membrane-bound LBP depend on the side of addition of the antiserum, indicating a directed intercalation of LBP into the membrane. Addition of LPS to the same side as LBP may induce a change of the conformation of LBP or its orientation in the membrane. Based on these observations, we propose that LBP intercalates in a directed orientation into negatively-charged membranes and assumes a transmembrane configuration. Moreover, pre-incubated complexes of LPS and LBP do not interact with membranes. These experiments show that reconstituted planar membranes are a suitable tool for investigations of the interaction of non pore-forming proteins that are involved in signal transduction.

Acute-Phase Proteins↗
PubMed1991

[Automatic, electronic determination of resting time in small laboratory animals and the effect of psychopharmaceuticals].

The free movements of a small laboratory animal on the bottom of a cage, containing capacitive sensors, are measured as electrical signals which are then amplified, classified in a classification device and counted. With reference to the class of the highest sensitivity and by the choice of appropriate device parameters, signals are only counted during the time in which animal movements are below a level defined as rest. By this, the resting time can be determined which expresses the time in which animals are in the defined rest during the whole test time. The ED50, namely the doses after which the resting time increases by 50% during the first 10 min of the exploration phase of mice has been determined of diazepam, chlordiazepoxide, haloperidol, droperidol, fluphenazine, butaperazine, 7-fluorobutaperazine, and chlorpromazine and it was compared with the ED 50 determined in the contact bottom plates motimeter according to Knoll et al. in mice and in the catalepsy test according to Wirth et al. in rats. respectively. The method of resting time determination has proved as to be striking more sensitive (5- to 10-fold) than the other methods.

Animals↗
PubMedDate not supplied

Simple electrical model of the circulation to explore design parameters for a skeletal muscle ventricle.

To efficiently investigate a variety of designs for an accessory skeletal muscle ventricle for circulatory assistance, we developed an electrical model of the human circulatory system. Heart and blood vessels were modeled as resistive-capacitive networks, pressures as voltages, blood flow as electric current, and the cardiac valves as diodes. Pumping of blood was simulated by the application of damped rectangular voltage pulses to the capacitances of the cardiac ventricles and the skeletal muscle ventricle. Three configurations of a skeletal muscle ventricle were studied: the apico-aortic, in which the skeletal muscle ventricle is interposed between the left ventricle and the abdominal aorta; the aorto-aortic, in which the skeletal muscle ventricle is interposed between the thoracic aorta and the abdominal aorta; and the atrial-aortic, in which the skeletal muscle ventricle is interposed between the left atrium and abdominal aorta. The three skeletal muscle ventricle designs were tested as counterpulsatile assist devices in simulations of the normal circulation and congestive heart failure. Performance of the various skeletal muscle ventricle designs was evaluated by comparing total output, mean left ventricular power expenditure, mean skeletal muscle ventricle power expenditure, and mean perfusion pressure of the skeletal muscle comprising the pouch. Under both normal heart and heart failure conditions, the apico-aortic design was superior to the aorto-aortic and to the atrial-aortic designs. With optimal stimulation parameters, the apico-aortic design reduced left ventricular minute work to 16% of normal during simulated heart failure while maintaining a viable resting cardiac output of 3.4 L/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Circulation↗
PubMed1994

Studies of cell pellets: I. Electrical properties and porosity.

Cell pellets formed by centrifugation provided a good system to study the osmotic behavior, electroporation, and interaction between cells. Rabbit erythrocyte pellets were used in this study because they were simpler than nucleated cells to model analytically. Structurally, cell pellets possessed properties of porous solid bodies and gels. Electrically, cell pellets were shown to behave as a parallel set of resistance, Rp, and capacitance, Cp. Information on pellet structures was obtained from electric measurements. The pellet resistance reflected the intercellular conductivity (porosity and gap conductivity), whereas the pellet capacitance depended mostly on membrane capacitance. The pellet resistance was more sensitive to experimental conditions. The intercellular gap distance can be derived from pellet porosity measurements, providing the cell volume and surface area were known. Rp increased and relaxed exponentially with time when centrifugation started and stopped; the cycles were reversible. When supernatants were exchanged with solutions containing hypotonic electrolytes or macromolecules (such as PEG) after the pellets were formed, complicated responses to different colloidal osmotic effects were observed. A transient decrease followed by a large increase of Rp was observed after the application of a porating electric pulse, as expected from a momentary membrane breakdown, followed by a limited colloidal-osmotic swelling of pelleted cells. The equilibrium values of Rp, Cp, pellet porosity, and intercellular distances were measured and calculated as functions of cell number, centrifugation force, and ionic strength of the exchanged supernatant. Thus, the structure and properties of cell pellets can be completely characterized by electrical measurements.

Animals↗
PubMed2005

A finite difference model for cMUT devices.

A finite difference method was implemented to simulate capacitive micromachined ultrasonic transducers (cMUTs) and compared to models described in the literature such as finite element methods. Similar results were obtained. It was found that one master curve described the clamped capacitance. We introduced normalized capacitance versus normalized bias voltage and metallization rate, independent of layer thickness, gap height, and size membrane, leading to the determination of a coupling factor master curve. We present here calculations and measurements of electrical impedance for cMUTs. An electromechanical equivalent circuit was used to perform simulations. Our experimental measurements confirmed the theoretical results in terms of resonance, anti-resonance frequencies, clamped capacitance, and electromechanical coupling factor. Due to inhomogeneity of the tested element array and strong parasitic capacitance between cells, the maximum coupling coefficient value achieved was 0.27. Good agreement with theory was obtained for all findings.

Computer Simulation↗
PubMed1999

[Electrical injuries during laparoscopy].

Electrical injury is uncommon during surgical laparoscopy, but may be serious. Following a comprehensive literature review, we describe five mechanisms of burn injuries: direct contact, electric arc, insulation failure, direct or capacitive coupling. We discuss these mechanisms and suggest simple preventive measures designed to ensure optimal safety.

Burns, Electric↗
PubMed2004

Social regulation of the electrical properties of gonadotropin-releasing hormone neurons in a cichlid fish (Astatotilapia burtoni).

Variation in reproductive capacity is common across the lives of all animals. In vertebrates, hypothalamic neurons that secrete GnRH are a primary mediator of such reproductive plasticity. Since social interactions suppress gonadal maturity in the African cichlid fish, Astatotilapia (Haplochromis) burtoni, we investigated whether the electrical properties of GnRH neurons were also socially regulated. Adult A. burtoni males are either territorial (T) and reproductively active or nonterritorial (NT) and reproductively regressed, depending upon their social environment. We compared the basic electrical properties of hypothalamic GnRH neurons from T and NT males using whole-cell electrophysiology in vitro. GnRH neurons were spontaneously active and exhibited several different activity patterns. A small fraction of neurons exhibited episodic activity patterns, which have been described in GnRH neurons from mammals. The type of activity pattern and spontaneous firing rate did not vary with reproductive capacity; however, several basic electrical properties were different. Neurons from T males were larger than those from NT males and had higher membrane capacitance and lower input resistance. In neurons from NT males, action potential duration was significantly longer and after-hyperpolarization characteristics were diminished, which led to a tendency for neurons from NT males to fire less rapidly in response to current injection. We predict this could serve to decrease GnRH release in NT males. These data are the first electrophysiological characterization of hypothalamic GnRH neurons in a nonmammalian species and provide evidence for several changes in electrical properties with reproductive state.

Action Potentials↗
PubMed2001

Perchlorate stimulates insulin secretion by shifting the gating of L-type Ca2+ currents in mouse pancreatic B-cells towards negative potentials.

The effects of the chaotrophic anion perchlorate (ClO4-) on glucose-induced electrical activity, exocytosis and ion channel activity in mouse pancreatic B-cells were investigated by patch-clamp recordings and capacitance measurements. ClO4- stimulated glucose-induced electrical activity and increased the action potential frequency by 70% whilst not affecting the membrane potential when applied in the presence of a subthreshold concentration of the sugar. ClO4- did not influence ATP-dependent K (KATP) channel activity and voltage-gated delayed K+ current. Similarly, ClO4- had no effect on Ca2+-dependent exocytosis. The stimulation of electrical activity and insulin secretion was instead attributable to an enhancement of the whole-cell Ca2+ current. This effect was particularly pronounced at voltages around the threshold for action potential initiation and a doubling of the current amplitude was observed at -30 mV. This was due to a 7-mV shift in the gating of the Ca2+ current towards negative voltages. The action of ClO4- was more pronounced when added in the presence of 0.1 mM BAY K8644, whereas no stimulation was observed when applied at a maximal concentration of the agonist (1 mM). Single-channel recordings revealed that the effect of ClO4- on whole-cell currents was principally due to a 60% increase in the mean duration of the long openings and the number of active channels. We propose that ClO4- stimulates insulin secretion and electrical activity by exerting a BAY K8644-like action on Ca2+ channel gating.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗