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At least 1,063 records · Page 59Linked to original sources
PubMed2005

Physiological properties of rod photoreceptor electrical coupling in the tiger salamander retina.

Using dual whole-cell voltage and current clamp recording techniques, we investigated the gap junctional conductance and the coupling coefficient between neighbouring rods in live salamander retinal slices. The application of sinusoidal stimuli over a wide range of temporal frequencies allowed us to characterize the band-pass filtering properties of the rod network. We found that the electrical coupling of all neighbouring rods exhibited reciprocal and symmetrical conductivities. On average, the junctional conductance between paired rods was 500 pS and the coupling coefficient (the ratio of voltage responses of the follower cell to those of the driver cell), or K-value, was 0.07. Our experimental results also demonstrated that the rod network behaved like a band-pass filter with a peak frequency of about 2-5 Hz. However, the gap junctions between adjacent rods exhibited linearity and voltage independency within the physiological range of rods. These gap junctions did not contribute to the filtering mechanisms of the rod network. Combined with the computational modelling, our data suggest that the filtering of higher frequency rod signals by the network is largely mediated by the passive resistive and capacitive (RC) properties of rod plasma membranes. Furthermore, we found several attributes of rod electrical coupling resembling the physiological properties of gene-encoded Cx35/36 gap junctions examined in other in vitro studies. This indicates that the previously found Cx35/36 expression in the salamander rod network may be functionally involved in rod-rod electrical coupling.

Action Potentials↗
PubMed1982

Properties of a microcoaxial electrode designed for unit recording from human peripheral nerves.

A new microcoaxial electrode is presented, which has been used successfully for recording single- and multiunit activity from myelinated and unmyelinated human nerve fibres. The main advantages (as compared with conventional needle electrodes) are electrical stability, mechanical durability, capability of being re-used and an insulation not easily scraped off, resulting in a low leakage capacitance. The AC polarization impedance and the potential transducing properties of the microelectrode have also been studied.

Electric Conductivity↗
PubMed1996

Factors affecting electrode-gel-skin interface impedance in electrical impedance tomography.

The magnitude, mismatch and temporal variations of the electrode-gel-skin interface impedance can cause problems in electrical impedance tomography (EIT) measurement. It is shown that at the high frequencies generally encountered in EIT the capacitive properties of the electrode interface, and especially those of the skin, are of primary importance. A wide range of techniques are reviewed that could possibly be used to minimise these problems. These techniques include the use of skin preparation, penetration enhancers, temperature and electrical impulses. Although several of these techniques appear very attractive, they are not without serious potential drawbacks. A combination of some of these techniques may well hold the key to success.

Electric Impedance↗
PubMed1976

Effects of deuterium oxide on mechano-sensory receptor.

In the crayfish stretch receptor organ, a total substitution of D2O for H2O in the bathing solution produced a decrease in the amplitude of the receptor potential to a level of 34% of the control. The electrical resistance of the receptor neuron was slightly increased by the D2O substitution. The input capacitance of the neuron was unchanged. The viscoelastic properties of the receptor muscle were not altered by D2O. Thus, we conclude that D2O has an inhibitory effect on the transduction process which links the deformation of the dendrites with the permeability increase that is responsible for the receptor potential.

Action Potentials↗
PubMed1997

Permeation of phloretin across bilayer lipid membranes monitored by dipole potential and microelectrode measurements.

The transmembrane diffusion of phloretin across planar bilayer lipid membranes is studied under steady-state conditions. Diffusion restrictions and adsorption related effects are measured independently. The adsorption of aligned phloretin dipoles generates a change in the intrinsic dipole potential difference between the inner and outer leaflets of the lipid bilayer. It is monitored by capacitive current measurements carried out with a direct current (dc) bias. The variation of the intramembrane electric field indicates a saturation of the binding sites at the membrane interface. In contrast, pH profile measurements undertaken in the immediate membrane vicinity show a constant membrane permeability. If phloretin binding and transmembrane diffusion are treated as two competitive events rather than subsequent steps in the transport queue the contradictory results become explainable. A mathematical model is developed where it is assumed that diffusing phloretin molecules are randomly oriented, i.e., that they do not contribute to the intrinsic membrane potential. Only the dipoles adsorbing onto the membrane are oriented. Based on these theory the membrane permeability is calculated from the capacitive current data. It is found to agree very well with the permeability deduced from the microelectrode measurements.

Adsorption↗
PubMed1988

Increased cAMP production after short-term capacitively coupled stimulation in bovine growth plate chondrocytes.

Growth plate chondrocytes from newborn calf costochondral junctions grown in monolayer were subjected to a capacitive AC signal of 500 V peak to peak (P-P) at 60 kHz for 48 h and were analyzed for [3H]thymidine uptake. The stimulated chondrocytes showed a 130% greater uptake over unstimulated controls. Other newborn calf growth plate chondrocytes were stimulated at 500 V P-P at 60 kHz for 2.5, 5.0, 10.0, and 20.0 min and were analyzed for cAMP. Chondrocytes stimulated for 2.5 and 5.0 min showed a 142.8% (p less than 0.05) and 394.5% (p less than 0.01) increase over controls, respectively. The chondrocytes stimulated for 10.0 and 20.0 min showed no significant difference from the controls. It is concluded that short-term exposure of growth plate chondrocytes to an appropriate capacitively coupled field stimulates cAMP production, but longer-term application of the electrical field is ineffective.

Animals↗
PubMed2006

The regulatory role of mitochondria in capacitative calcium entry.

Capacitative regulation of calcium entry is a major mechanism of Ca2+ influx into electrically non-excitable cells, but it also operates in some excitable ones. It participates in the refilling of intracellular calcium stores and in the generation of Ca2+ signals in excited cells. The mechanism which couples depletion of intracellular calcium stores located in the endoplasmic reticulum with opening of store-operated calcium channels in the plasma membrane is not clearly understood. Mitochondria located in close proximity to Ca2+ channels are exposed to high Ca2+ concentration, and therefore, they are able to accumulate this cation effectively. This decreases local Ca2+ concentration and thereby affects calcium-dependent processes, such as depletion and refilling of the intracellular calcium stores and opening of the store-operated channels. Finally, mitochondria modulate the intensity and the duration of calcium signals induced by extracellular stimuli. Ca2+ uptake by mitochondria requires these organelles to be in the energized state. On the other hand, Ca2+ flux into mitochondria stimulates energy metabolism. To sum up, mitochondria couple cellular metabolism with calcium homeostasis and signaling.

Animals↗
PubMed2004

Large dense-core vesicle exocytosis in pancreatic beta-cells monitored by capacitance measurements.

This article discusses the currently used methodologies for monitoring exocytosis as changes in cell capacitance. Details are given on composition of solutions, experimental protocols, and how the observed responses can be interpreted physiologically. The concepts are illustrated by examples from our own work on insulin-releasing pancreatic beta-cells. Finally, we consider the feasibility of applying capacitance measurements to endocrine cells in intact pancreatic islets, where the cells are electrically coupled to each other.

Animals↗
PubMed1978

Effect of ultrasound on a bilayer lipid membrane.

The effects of continuous wave ultrasound at a frequency of 1 MHz in the intensity range of 0-1.4 W/cm2 on an oxidized cholesterol bilayer lipid membrane (BLM) were observed. Ultrasound at 1.5 W/cm2 broke the membrane; in the range from 0.5 to 1.4 W/cm2, it accelerated the draining of the bulk lipid solution from the annulus to the Teflon support. At all intensities it has no effect on the conductance, the capacitance, or the dependence of each on the voltage applied across the membrane. Electrical parameters were measured in the presence of aqueous solutions of NaCl, KCl, and distilled water. The motivation and results of this project are explained in relation to an overall objective of determining the specific effects of ultrasound on biological membranes.

Cholesterol↗
PubMed2003

Real-time measurement of exocytosis and endocytosis using interference of light.

We describe a new approach for making real-time measurements of exocytosis and endocytosis in neurons and neuroendocrine cells. The method utilizes interference reflection microscopy (IRM) to image surface membrane in close contact with a glass coverslip (the "footprint"). At the synaptic terminal of retinal bipolar cells, the footprint expands during exocytosis and retracts during endocytosis, paralleling changes in total surface area measured by capacitance. In chromaffin cells, IRM detects the fusion of individual granules as the appearance of bright spots within the footprint with spatial and temporal resolution similar to total internal reflection fluorescence microscopy. Advantages of IRM over capacitance are that it can monitor changes in surface area while cells are electrically active and it can be applied to mammalian neurons with relatively small synaptic terminals. IRM reveals that vesicles at the synapse of bipolar cells rapidly collapse into the surface membrane while secretory granules in chromaffin cells do not.

Animals↗
PubMed1980

Effect of glycerol treatment on the calcium current of frog skeletal muscle.

1. Current and voltage clamp experiments were carried out on frog skeletal muscle fibres. For voltage clamp, the three micro-electrode technique near the fibre end was used. 2. Calcium spikes and currents were recorded in TEA sulphate saline. The addition of 400 mM-glycerol did not appreciably modify them. 3. Muscle fibers were detubulated with the glycerol method. They showed sodium propagating action potentials, with sodium and potassium currents of expected amplitudes. 4. Calcium spikes and currents were reduced or abolished in detubulated muscle fibres. 5. An analysis of fibre capacitance showed a linear correlation between the remaining ICa and the degree of electric discontinuity between the transverse tubular system and the surface membrane. 6. These results indicate that ICa is mainly located in the transverse tubular system. This localization is compatible with some role during mechanical activation.

Action Potentials↗
PubMed2003

Response of a silicon photodiode to pulsed radiation.

Both the integrated-charge and the peak-voltage responsivity of a 1-cm2 Si photodiode optimized for the extreme ultraviolet have been measured with 532-nm-wavelength pulsed radiation. The peak power of the optical pulse is varied from 35 mW to 24 kW with a pulse width of 8.25 ns. A decrease in responsivity is observed with increasing pulse energy, and a model is presented that accounts for the observed loss of responsivity. The integrated-charge responsivity decreases because the presence of photogenerated majority carriers increases the direct recombination rate. The peak-voltage responsivity is reduced because the electric susceptibility of the electrons and holes in the depletion region increases the capacitance of the device. The influence of an applied reverse bias on both responsivities is investigated. The integrated-charge responsivity is found to be identical, with a 1% uncertainty, to the cw responsivity of the device if the energy dependence is considered.

Journal Article↗
PubMed2006

Multiparametric sensor-chip based technology for monitoring metabolic activity: A proof-of-principle study with live tissue.

The recent development of an electronic test system based on silicon sensor-chips allows the continuous parallel recording of relative changes in extracellular acidification, oxygen consumption and electric impedance in living cells. The objective of this proof-of-principle study therefore, was to clarify whether this system can also be applied to live tissue slices thus providing a device for an ultimately envisioned chemosensitivity testing apparatus for individualized treatment schemes in cancer therapy. A prototype of the testing apparatus equipped with six individual measuring devices has been used to simultaneously analyze changes in extracellular acidification, oxygen consumption and electronic impedance in live liver tissue and compared to data obtained from a tumor cell line. In contrast to tumor cells, tissue slices showed low rates of extracellular acidification but high rates of oxygen consumption. Monitoring of electrical impedance values, reflecting cellular morphology, revealed that the compact cell structure of the tissue slices was able to function as electric insulator and actively change the impedance values of the system. Exposure of tumor cells to 1 microM cytochalasin B, a fungal metabolite known to interact with the cytoskeleton and influence glucose metabolism, resulted in the rapid decline of extracellular acidification, increased oxygen consumption rates and increased values in capacitance. In tissue slices upon addition of 1 microM cytochalasin B, a decline of both extracellular acidification and electrical impedance was observed within 1 h. Determination of ATP content in the tissue slices revealed that decreasing ATP content paralleled diminishing oxygen consumption. This new technique offers the possibility of generating metabolic profiles for cells and tissues by studying oxygen consumption, extracellular acidification and electrical impedance.

Acid-Base Equilibrium↗