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PubMed1979

Temperature dependence on the passive and dynamic electrical parameters of muscle cells.

Measurements of the temperature dependence in the range from 10 C to 30 C on the passive and dynamic electrical properties of single frog muscle cell following Arrhenius relation have been made. The propagated responses (V-t) and conduction velocity theta were analyzed following the H-H propagated cable equation. The ionic current-membrane potential relationship (I-t) was calculated from the phase-plane trajectory analysis (V-V) of the action potential curve (V-t). All the rate and time constants of the excitation and propagation processes kr, kNa, kK, tau Na, tau K, the negative conductance (-gNa) and the ionic conductances gNa, gK, influencing the evolution of the curves (V-t), (V-V) and (I-V) are correlated. The magnitudes of the resting (Vr) and action potential amplitude (Vs), the excitation potential (V*), the negative after potential (Vn), and the sodium equilibrium potential (VNa); the magnitudes of the maximum rate of rise and fall of the spike (V+) and (V-) and those corresponding to the inward INa and outward IK ionic currents, were analyzed. Two general classes of findings were obtained. One group of action potential parameters theta, V+, V-, Vn, kr, kNa, kK, tau Na, tau K, -gNa, gNa, gK, INa and IK is strongly temperature dependent with Q 10 S approximately 2 and energy of activation E approximately 10 kcal/mole. The other group of parameters, Gm (passive conductance), Cm (capacitance), tau, Vr, V*, Vs, and VNa are slightly temperature dependent, with Q10's lower than 1.4. This study contributes deeply to the analysis of temperature effects on the electrical cell responses to adequate stimuli. This temperature dependence analysis was designed to detect possible "masked" actions of microwave radiation on cell membrane functions.

Action Potentials↗
PubMed1984

Fourier analysis of effects of varying pressure waveforms in electrical lung analogs.

Six voltage waveforms were devised to simulate pressure curves of varying configuration for use in artificial ventilation. These waveforms were subjected to Fourier analysis and terms of the resulting series applied to a simple two-branch resistive-capacitive circuit intended to represent a lung analog using computer simulation. Current (analogous to flow) and charge (analogous to volume) in each branch could be graphically displayed. Differences among the waveforms in such attributes as efficiency, inspiratory work, volume introduced per unit of mean pressure applied, and relative volume distribution between the two branches could be demonstrated. All waveforms were capable of delivering a predetermined volume to the circuit with adjustment of their peak pressure (voltage). It was not possible to designate any of the waveforms as "superior" since advantage in one attribute, such as efficiency, was accompanied by deficiencies in other characteristics such as uneven volume distribution. Despite obvious severe limitations on physiological interpretations of such data, Fourier analysis of respiratory waveforms appears to be a useful teaching, illustrative, and exploratory method.

Computers↗
PubMed1992

Ca(2+)-activated and voltage-gated K+ currents in smooth muscle cells isolated from human mesenteric arteries.

1. Smooth muscle cells were enzymatically isolated from arteries dissected from mesenteric fat removed from patients undergoing routine surgery. The whole-cell patch clamp technique was used to characterize the potassium (K+) currents and passive electrical properties of these cells, using high-K(+)-containing pipette solutions with either 0.2 mM EGTA or 10 mM EGTA and 10 mM BAPTA. 2. Cell capacitance, which is proportional to membrane surface area, was normally distributed around a value of 46 pF, and independent of artery size between 0.4 and 3.6 mm. The mean membrane potential measured under current clamp was -44.1 +/- 1.9 mV (n = 52). 3. Cells dialysed with 0.2 mM EGTA in order to weakly buffer intracellular Ca2+ demonstrated a noisy outward current with an apparent threshold near -30 mV, upon which were superimposed spontaneous transient outward currents (STOCs). In the presence, but not the absence, of extracellular Ca2+, this current was potentiated if the holding potential was depolarized into the voltage range between -40 and +50 mV. This potentiation had a bell-shaped potential dependency which reflected the activation of voltage-gated Ca2+ channels in these cells. 4. The noisy current was blocked by externally applied tetraethylammonium (the dissociation constant, Kd = 0.85 mM), as were STOCs. This current was also reduced by about 40% by 8 nM charybdotoxin, and was transiently potentiated by 10 mM caffeine. The characteristics of this current therefore suggested that it was carried by large-conductance Ca(2+)-activated K+ channels. 5. Dialysis of human mesenteric arterial cells with 10 mM EGTA and 10 mM BATPA was not able to completely suppress the Ca(2+)-activated current, and reduced by approximately 50% the amplitude of the outward current recorded at positive potentials. 6. Depolarization of strongly Ca(2+)-buffered cells in the presence of 30 mM TEA to block Ca(2+)-activated K+ channels revealed a residual outward current which had both transient and sustained components. These were blocked by 4-aminopyridine (4-AP) with a similar efficiency (Kd was 1.04 and 1.16 mM at +60 mV for transient and sustained current, respectively), but the voltage ranges over which they inactivated, and their rates of recovery from inactivation, were significantly different. 7. The transient and sustained currents had different sensitivities to external Ca2+ and Cd2+ ions. Ca2+ (5 mM) significantly reduced the amplitude and shifted the voltage dependency of inactivation of the transient but not the sustained component of the outward current. Cd2+ (0.2 mM) reduced the transient current by about 30% without affecting the sustained component amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Cadmium↗
PubMed1987

Fast charge translocations associated with partial reactions of the Na,K-pump: I. Current and voltage transients after photochemical release of ATP.

Nonstationary electric currents are described which are generated by the Na,K-pump. Flat membrane sheets 0.2-1 micron in diameter containing a high density of oriented Na,K-ATPase molecules are bound to a planar lipid bilayer acting as a capacitive electrode. In the aqueous phase adjacent to the bound membrane sheets, ATP is released within milliseconds from an inactive, photolabile precursor ("caged" ATP) by an intense flash of light. After the ATP-concentration jump, transient current and voltage signals can be recorded in the external circuit corresponding to a translocation of positive charge across the pump protein from the cytoplasmic to the extracellular side. These electrical signals which can be suppressed by inhibitors of the Na,K-ATPase require the presence of Na+ but not of K+ in the aqueous medium. The intrinsic pump current Ip(t) can be evaluated from the recorded current signal, using estimated values of the circuit parameters of the compound membrane system. Ip(t) exhibits a biphasic behavior with a fast rising period, followed by a slower decline towards a small quasi-stationary current. The time constant of the rising phase of Ip(t) is found to depend on the rate of photochemical ATP release. Further information on the microscopic origin of the current transient can be obtained by double-flash experiments and by chymotrypsin modification of the protein. These and other experiments indicate that the observed charge-translocation is associated with early events in the normal transport cycle. After activation by ATP, the pump goes through the first steps of the cycle and then enters a long-lived state from which return to the initial state is slow.

Adenosine Triphosphate↗
PubMed1987

Simultaneous electrical and optical measurements show that membrane fusion precedes secretory granule swelling during exocytosis of beige mouse mast cells.

Mast cells show dramatic morphological changes when undergoing exocytosis. We have investigated whether the first of those morphological changes, swelling of the secretory granule, precedes--and therefore possibly initiates--secretion or whether it occurs after fusion of the granule and plasma membranes. We used cell membrane capacitance to detect the moment when granule and plasma membrane become continuous. We measured large capacitance increases, often preceded by transients in capacitance. The rise-times of the capacitance increases were half-maximal at 2-59 msec. We observed cells with high-resolution video microscopy while these measurements were done. The capacitance increase always preceded the granular swelling that leads to exocytosis. To rule out the possibility that fusion was induced by a mechanical stress imparted by the internal pressure of a taut granule, we performed control experiments using cells in which vesicles were shrunken with hyperosmotic solutions. With these flaccid granules, again, the capacitance rise always preceded the swelling of the granules. We conclude that swelling cannot be the driving force for membrane fusion in this system.

Animals↗
PubMed1976

Voltage-induce capacitance relaxation of lipid bilayer membranes. Effects of membrane composition.

The specific capacity of black lipid membranes of different phospholipids dissolved in n-alkanes was investigated. The hydrocarbon thickness of these membranes, as calculated from the electric capacity with a dielectric constant of 2.1, was in most cases close to 5 nm. It was found that the specific capacity is not constant with time after blackening. It shows a linear time dependence characteristic for each lipid/solvent system. The influence of a transmembrane potential on the capacity of the membranes was measured. It was shown that the extent of the capacity change, obtained 10 s after applying a voltage, was strongly dependent on the lipid composition as well as the solvent content of the membranes. The capacity change of the membranes seems to be caused mainly by a thickness change and not by an area increase of the membranes.

Electric Conductivity↗
PubMed1990

The proteoliposomal steady state. Effect of size, capacitance and membrane permeability on cytochrome-oxidase-induced ion gradients.

1. The flux pathways for H+ and K+ movements into and out of proteoliposomes incorporating cytochrome c oxidase have been investigated as a function of the electrical and geometrical properties of the vesicles. 2. The respiration-induced pH gradient (delta pH) and membrane potential (delta psi) are mutually dependent and individually sensitive to the permeability properties of the membrane. A lowering or abolition of delta psi by the addition of valinomycin increased the steady-state level of delta pH. Conversely, removal of delta pH by the addition of nigericin resulted in a higher steady-state delta psi. 3. Vesicles prepared by sonication followed by centrifugation maintained similar pH gradients at steady state to those in vesicles prepared by dialysis, although the time taken to reach steady state was longer. Higher pH gradients can be induced in non-centrifuged sonicated preparations. 4. No significant differences were found in H+ and K+ permeability between proteoliposomes prepared by dialysis or by sonication. The permeability coefficient of the vesicle bilayers for H+ was 6.1 x 10(-4) cm.s-1 and that for K+ was 7.5 x 10(-10) cm.s-1. An initial fast change in internal pH was seen on the addition of external acid or alkali, followed by a slower, ionophore-sensitive, change. The initial fast phase can be increased by the lipid-soluble base dibucaine and the weak acid oleate. In the absence of ionophores, increasing concentrations of oleate increased the rate of H+ translocation to a level similar to that seen in the presence of nigericin. Internal alkalinization could also be induced by oleate upon the addition of potassium sulphate. 5. The initial, pre-steady-state and steady-state delta pH and delta psi changes can be simulated using a model in which the enzyme responds to both delta pH and delta psi components of the protonmotive force. At steady state, the electrogenic entry of K+ is countered by electroneutral exit via a K+/H+ exchange. 6. The permeability coefficient, PH, calculated from H+ flux under steady-state turnover conditions, was approx. 100 times higher than the corresponding 'passive' measurements of PH. Under conditions of oxidase turnover, the vesicles appear to be intrinsically more permeable to protons.

Animals↗
PubMed1987

Rabbit oocyte maturation: changes of membrane resistance, capacitance, and the frequency of spontaneous transient depolarizations.

Immature oocytes from rabbits were examined with electrophysiological techniques to determine if their membrane properties change during maturation. The input resistance increased and input capacitance decreased during maturation, although no significant change in membrane potential was observed. The changes observed were consistent with a decrease of corona radiata-oocyte electrical coupling accompanying maturation. Spontaneous transient depolarizations were recorded from immature oocytes surrounded by corona radiata, but not from mature ova. Each event consisted of a rapid depolarization, sustained for 1-100 sec, and a slow repolarization to the resting potential. Spontaneous inward currents with a time course similar to the spontaneous transient depolarizations occurred when the oocyte's membrane potential was held constant by voltage clamp. The frequency with which spontaneous transient depolarizations occurred decreased during maturation. These findings are consistent with a model in which spontaneous depolarizations originate in corona radiata cells and are detected in the oocyte via electrical coupling.

Action Potentials↗
PubMed2006

TRPM4 controls insulin secretion in pancreatic beta-cells.

TRPM4 is a calcium-activated non-selective cation channel that is widely expressed and proposed to be involved in cell depolarization. In excitable cells, TRPM4 may regulate calcium influx by causing the depolarization that drives the activation of voltage-dependent calcium channels. We here report that insulin-secreting cells of the rat pancreatic beta-cell line INS-1 natively express TRPM4 proteins and generate large depolarizing membrane currents in response to increased intracellular calcium. These currents exhibit the characteristics of TRPM4 and can be suppressed by expressing a dominant negative TRPM4 construct, resulting in significantly decreased insulin secretion in response to a glucose stimulus. Reduced insulin secretion was also observed with arginine vasopressin stimulation, a Gq-coupled receptor agonist in beta-cells. Moreover, the recruitment of TRPM4 currents was biphasic in both INS-1 cells as well as HEK-293 cells overexpressing TRPM4. The first phase is due to activation of TRPM4 channels localized within the plasma membrane followed by a slower secondary phase, which is caused by the recruitment of TRPM4-containing vesicles to the plasma membrane during exocytosis. The secondary phase can be observed during perfusion of cells with increasing [Ca(2+)](i), replicated with agonist stimulation, and coincides with an increase in cell capacitance, loss of FM1-43 dye, and vesicle fusion. Our data suggest that TRPM4 may play a key role in the control of membrane potential and electrical activity of electrically excitable secretory cells and the dynamic translocation of TRPM4 from a vesicular pool to the plasma membrane via Ca(2+)-dependent exocytosis may represent a key short- and midterm regulatory mechanism by which cells regulate electrical activity.

Animals↗
PubMed1999

Selectivity of prandial glucose regulators: nateglinide, but not repaglinide, accelerates exocytosis in rat pancreatic A-cells.

The effects of the two prandial glucose regulators, repaglinide and nateglinide, on ATP-sensitive K(+) (K(ATP)) channel activity, membrane potential and exocytosis in single rat pancreatic A-cells were investigated using the patch-clamp technique. K(ATP) channel activity was reversibly blocked by repaglinide (K(d)=22 nM) and nateglinide (K(d)=410 nM) and this was associated with membrane depolarisation and initiation of electrical activity. The effect of repaglinide and nateglinide on stimulation of glucagon secretion by direct interference with the exocytotic machinery was investigated by the use of capacitance measurements. Nateglinide, but not repaglinide, at concentrations similar to those required to block K(ATP) channels potentiated Ca(2+)-evoked exocytosis 3-fold. In alphaTC1-9 glucagonoma cells addition of nateglinide, but not repaglinide, was associated with stimulation of glucagon secretion. These results indicate that the fast-acting insulin secretagogue nateglinide is glucagonotropic primarily by stimulating Ca(2+)-dependent exocytosis.

ATP-Binding Cassette Transporters↗
PubMed1999

Basolateral store-operated Ca(2+)-entry in polarized human bronchial and colonic epithelial cells.

Bronchial epithelial cells respond to extracellular nucleotides from the luminal and basolateral side activating Cl- secretion via [Ca2+]i increase. In this study we investigated the differences of apically (ap) and basolaterally (bl) stimulated [Ca2+]i signals in polarized human bronchial epithelial cells (16HBE14o-). Specifically we investigated the localization of 'capacitative Ca2+ entry' (CCE). 16HBE14o- cells grown on permeable filters were mounted into an Ussing chamber built for the simultaneous measurement of Fura-2 fluorescence and electrical properties. Application of ATP from both sides induced a rapid [Ca2+]i increase and subsequent sustained [Ca2+]i plateau due to transmembraneous Ca(2+)-influx. The use of different nucleotides revealed the following rank order or potency which was very similar for addition from the apical or basolateral side: UTP (EC50 ap: 4 microM, bl: 5 microM) > ATP (EC50 ap: 4 microM, bl: 10 microM) > ADP (n = 4-7 from both sides). 2-MeS-ATP, AMP, adenosine and beta gamma-methylene ATP were ineffective (n = 3 from both sides). The ATP- (ap and bl) induced Ca2+ influx was only abolished by removal of basolateral Ca2+. This was also true for receptor-independent activation of Ca(2+)-influx by intracellular Ca(2+)-store depletion with 2,5 Di-(tert-butyl)-1,4-benzohydroquinone (BHQ) (10 microM). Also in polarized T84 cells the basolateral carbachol and BHQ activated Ca2+ plateau was exclusively sensitive to removal of basolateral Ca2+. We propose that in all polarized epithelial cells the CCE entry pathway is located in the basolateral membrane. We furthermore suggest that Ca2+[i elevating agonists acting from the apical side of the epithelium lead to the opening of a basolateral CCE pathway.

Adenosine Triphosphate↗
PubMed2002

In-vivo measurement of swine myocardial resistivity.

We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.

Animals↗
PubMed2005

An analytical model of multilayer ultrasonic transducers with an inversion layer.

Inversion layer ultrasonic transducers have been investigated recently as an interesting approach in wideband transducer design. In this paper we present an analytical model of multilayer ultrasonic transducers with an inversion layer. Our analysis of the wave propagation problem of an inversion layer transducer includes a functional decomposition of the electrical input impedance. It becomes clear from this decomposition that an inversion layer transducer can be modeled as three elements in series connection, i.e., a clamped capacitance, a classical motional impedance, and a coupled motional impedance. The first two elements make up the classical model of a single element transducer. The coupled motional impedance describes the coupled interaction between the regular and the inverted piezoelectric sublayers, and thus reflects the effect of an inversion layer. We present examples which show that inversion layer transducers are advantageous in achieving such useful features as dual-frequency operation mode as used in harmonic imaging or broadband performance desired in most ultrasonic applications.

Journal Article↗
PubMed1985

The effects of temperature acclimation on the resting membrane of skeletal muscle fibres from green sunfish.

Conductive properties of muscle fibres from green sunfish (Lepomis cyanellus) acclimated to different temperatures were examined. The relative membrane permeability to chloride and potassium ions, PCl/PK, measured at acclimation temperature, was approximately 7.0 after acclimation at 25 degrees C and 1.3 after acclimation at 7 degrees C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 degrees C as compared to 25 degrees C-acclimated fibres. Mean (+/- S.E.M.) values of the chloride conductance were 554 +/- 68 microseconds cm-2 in warm-acclimated sunfish, and 75 +/- 9 microseconds cm-2 in cold-acclimated sunfish. Membrane capacitance also differed significantly between the two acclimation groups. When the temperature was varied acutely, the magnitude of the chloride conductance exhibited a maximum Q10 of only 1.9, compared with a Q10 of 3.0 associated with acclimation. Upon transferring 25 degrees C-acclimated sunfish to holding tanks at 7 degrees C, the total membrane resistance exhibited a sigmoidal increase over about 14 days, and a steady membrane capacitance was achieved in about 10 days. For 7 degrees C-acclimated sunfish, transferred to 25 degrees C, resistance showed a sigmoidal decrease over 10 days and capacitance was steady after 8 days. The results indicate that thermal acclimation of the muscle membrane involves cellular regulatory processes which underlie significant changes in the electrical properties of the fibre.

Animals↗
PubMed1999

The future of research on electroreception and electrocommunication

Beyond continuation of currently active areas, some less studied ones are selected for predictions of marked advance. (1) Most discoveries will be in cellular components and molecular mechanisms for different classes of receptor or central pathways. (2) More major taxa, possibly birds, reptiles or invertebrates, will be found to have electroreceptive species representing independent evolutionary 'inventions'. (3) Electric organs with weak and episodic electric discharges will be found in new taxa; first, among siluriforms. (4) New examples are to be expected, such as lampreys, where synchronized muscle action potentials sum to voltages in the range of weakly electric fish. Some of these will look like intermediates in the evolution of electric organs. (5) Ethological significance will be found for a variety of known physiological features; e.g. uranoscopids, skates and weakly electric catfish with episodic electric discharges; electroreceptive ability of animals such as lampreys, chimaeras, lungfish, sturgeons, paddlefish and salamanders with Lorenzinian-type ampullae; gymnotiform and mormyrid detection of the capacitative component of impedance. (6) The organization of some higher functions in the cerebellum and forebrain will gradually come to light.

Journal Article↗
PubMed2006

Morphologic changes in boar sperm nuclei with reduced disulfide bonds in electrostimulated porcine oocytes.

In pigs, failure of sperm nuclear decondensation has been reported after injection into oocytes. We examined the effects of pretreating sperm heads with Triton X-100 (TX-100) and dithiothreitol (DTT) and of electrical stimulation of oocytes after sperm head injection on time-dependent morphologic changes in sperm nuclei and in vitro development to the blastocyst stage. In experiment 1, spermatozoa were pretreated with 1% TX-100 and 5 mM DTT (T + D) or not treated, and then injected into in vitro matured oocytes. Electrical stimulation (1.5 kV/cm, 20 mus DC pulse) was applied to the oocytes 1 h after injection (stimulated group) or was not applied (unstimulated group). Some of the oocytes in each group were evaluated at hourly intervals until 10 h after injection for morphologic changes in the sperm nuclei. Unstimulated oocytes injected with untreated spermatozoa showed a delayed peak in the rate of nuclear decondensation (39.4-44.1%, 3-6 h after injection) compared with oocytes injected with T + D-treated spermatozoa (57.0% and 52.6%, 1 and 2 h, respectively). The rate of male pronucleus formation peaked 6 h after stimulation (by 40-60%) after injected oocytes had been stimulated with an electrical pulse, irrespective of whether or not the spermatozoa had been pretreated. In unstimulated oocytes, the rate of male pronucleus formation did not increase and stayed at the basal level (less than 20%) throughout the culture period, regardless of the sperm treatment. Thus, T + D treatment of spermatozoa did not affect completion of fertilization. In experiment 2, we evaluated the effects of electrical stimulation and sperm treatment with T + D on the rate of blastocyst formation and the mean number of cells per blastocyst. Oocytes stimulated after injection with either T + D-treated or untreated spermatozoa showed significantly higher percentages of blastocyst formation (24.8% and 27.1% respectively) than did unstimulated oocytes (1.1% and 4.1% for T + D-treated and untreated respectively; P < 0.01 by Duncan's multiple-range test). The rate of blastocyst formation did not differ between the T + D-treated and untreated groups. The mean number of cells per blastocyst did not differ among any of the groups (14.0-29.4 cells). These results suggest that pretreatment of sperm with TX-100 and DTT shifted the timing of sperm nuclear decondensation forward. However, pronucleus formation and development to the blastocyst stage in vitro were not improved by sperm treatment. Thus, electrical stimulation of injected oocytes enhances in vitro development to the blastocyst stage in pigs.

Animals↗
PubMed1960

Electrical impedance changes of the cat's foot pad in relation to sweat secretion and reabsorption.

Impedance across the cat's foot pad, the glands being at rest, has a high quite constant value in a given preparation. Stimulation of the sudomotor nerves causes a decrease to a low constant value. After cessation of stimulation impedance returns slowly over a course that is linear with respect to the logarithm of time. The resistive and capacitative components vary with each other. Sweat reabsorption during recovery progresses linearly with respect to time. Hence impedance varies as the logarithm of reabsorption, and therefore as the mean level of sweat columns in the ducts. This relation can be accommodated by supposing that the sweat duct epithelium resembles a core conductor. An electrical model constructed on this principle is shown to behave as does the foot pad. During stimulation at a fixed frequency impedance change varies as the logarithm of duration showing that the amount of sweat produced per impulse at a given frequency is a constant. With frequency of a fixed number of stimuli varied the impedance change varies with it in a manner consistent with the view that the amount of sweat produced per impulse is a constant regardless of frequency.

Animals↗