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PubMed1998

Calcium signaling by cyclic ADP-ribose, NAADP, and inositol trisphosphate are involved in distinct functions in ascidian oocytes.

ADP-ribosyl cyclase catalyzes the synthesis of two structurally and functionally different Ca2+ releasing molecules, cyclic ADP-ribose (cADPR) from beta-NAD and nicotinic acid-adenine dinucleotide phosphate (NAADP) from beta-NADP. Their Ca2+-mobilizing effects in ascidian oocytes were characterized in connection with that induced by inositol 1,4,5-trisphosphate (InsP3). Fertilization of the oocyte is accompanied by a decrease in the oocyte Ca2+ current and an increase in membrane capacitance due to the addition of membrane to the cell surface. Both of these electrical changes could be induced by perfusion, through a patch pipette, of nanomolar concentrations of cADPR or its precursor, beta-NAD, into unfertilized oocytes. The changes induced by beta-NAD showed a distinctive delay consistent with its enzymatic conversion to cADPR. The cADPR-induced changes were inhibited by preloading the oocytes with a Ca2+ chelator, indicating the effects were due to Ca2+ release induced by cADPR. Consistently, ryanodine (at high concentration) or 8-amino-cADPR, a specific antagonist of cADPR, but not heparin, inhibited the cADPR-induced changes. Both inhibitors likewise blocked the membrane insertion that normally occurred at fertilization consistent with it being mediated by a ryanodine receptor. The effects of NAADP were different from those of cADPR. Although NAADP induced a similar decrease in the Ca2+ current, no membrane insertion occurred. Moreover, pretreatment of the oocytes with NAADP inhibited the post-fertilization Ca2+ oscillation while cADPR did not. A similar Ca2+ oscillation could be artificially induced by perfusing into the oocytes a high concentration of InsP3 and NAADP could likewise inhibit such an InsP3-induced oscillation. This work shows that three independent Ca2+ signaling pathways are present in the oocytes and that each is involved in mediating distinct changes associated with fertilization. The results are consistent with a hierarchical organization of Ca2+ stores in the oocyte.

ADP-ribosyl Cyclase↗
PubMed1992

Optimal electrolytic chloriding of silver ink electrodes for use in electrical impedance tomography.

The electrode-electrolyte interface impedance may be simplistically modelled by an equivalent circuit comprising a resistance, RTOTAL, in series with an empirical, constant phase angle impedance, ZCPA. This pseudo-capacitance can be thought of as representing empirically the non-faradaic, double layer capacitance in the presence of specific adsorption and surface roughness effects. RTOTAL is the sum of the lead and electrolyte resistances. Depositing a thin layer of silver chloride on silver electrodes can yield improved electrical performance characteristics (potential and impedance) when used in conjunction with a chloride gel. An electrolytically deposited AgCl layer tends to have a rough surface profile thus leading to an increase in the effective interface area. This gives rise to a decrease in RTOTAL and ZCPA, both of which are desirable. Unfortunately AgCl is a relatively poor conductor. Increasing layer thickness causes RTOTAL to increase, thus adversely affecting the inter-electrode impedance at high frequencies. Electrode systems for use in electrical impedance tomography therefore require only relatively thin layers of AgCl.

Electric Conductivity↗
PubMed1988

The rapid induction of the acrosome reaction of human spermatozoa by electropermeabilization.

Human spermatozoa are usually prepared for in vitro fertilization (IVF) by centrifugal washing and incubation in albumin based media. This is an inefficient technique contributing to poor IVF prospects, false-negative scores in the sperm penetration assay (SPA), and inadequate quantification in the sperm chromosome assay (SCA). High yields of fusiogenically functional sperm were rapidly and efficiently prepared by exposing sperm suspensions to an electrical pulse of 750 to 1500 V cm-1 for 2.5 msec. This process was calcium-dependent, and sperm incorporation into zona-free hamster eggs exhibited a linear relationship with Ca2+. At voltages greater than 1500 V cm-1, penetration declined. Sperm from subfertile men demonstrated significantly increased penetration after electropermeabilization. Sperm development was not hindered and in the SCA, yields of sperm metaphases approaching 100% were achievable.

Acrosome↗
PubMed2001

Stray radiofrequency current as a cause of urethral strictures after transurethral resection of the prostate.

PURPOSE: This study was designed to define the pattern and significance of stray currents induced by two electrosurgical generators (ESGs) in relation to urethral strictures forming after transurethral resection of the prostate (TURP). MATERIALS AND METHODS: A 24F resectoscope irrigated with glycine was activated at various power outputs in different modes, with intact loops and loops with faulty insulation, simulating TURP. The Valleylab and ERBE ESGs were compared for inducing capacitance. An ESG analyzer simulated tissue impedance and recorded the stray currents induced along the resectoscope sheath. A fresh pig liver was used for assessment of tissue damage caused by the currents. RESULTS: In the cutting mode, the ERBE ESG produced a mean stray current of 70 mA with an intact loop and 144 mA with a loop having faulty insulation. The Valleylab ESG produced 150 mA and 161 mA, respectively. In the coagulation mode, the ERBE ESG produced an average leakage current of 35 mA and, with a loop with faulty insulation, 40 mA. The Valleylab ESG produced 148 mA and 151 mA, respectively. CONCLUSIONS: Electrical injury may represent a significant cause of urethral stricture after transurethral electrosurgery. The critical power density of 7.5 W/cm2 (which is likely to cause a urethral burn) may be reached, especially with the use of loops with faulty insulation or nonconductive lubricating gel. The ERBE ESG produced significantly less capacitance, decreasing the risk of urethral electrical burn. Conductive gel prevents dangerous current concentration.

Electric Injuries↗
PubMed1997

The influence of the subsurface cisterna on the electrical properties of the outer hair cell.

A distributed-parameter computational model of the outer hair cell was used to predict the potentials resulting from current injection. A good fit was found to the length-dependent whole cell conductance and capacitance. The fit required the presence of the subsurface cisterna and a low (0.001 mS/cm2) specific conductivity for the plasma membrane of the lateral wall. The lateral wall could not be space clamped as significant longitudinal currents pass through the extracisternal space vs the axial core. A reduction in the width of the extracisternal space decreased the whole-cell conductance and capacitance. Position-dependent phase shifts were noted during injection of sinusoidal currents (0.001575 rad/micron). These predictions support a role for extracisternal longitudinal potential gradients in experimentally observed non-linear capacitance and electromotility.

Animals↗
PubMed2001

Model channel ion currents in NaCl-extended simple point charge water solution with applied-field molecular dynamics.

Using periodic boundary conditions and a constant applied field, we have simulated current flow through an 8.125-A internal diameter, rigid, atomistic channel with polar walls in a rigid membrane using explicit ions and extended simple point charge water. Channel and bath currents were computed from 10 10-ns trajectories for each of 10 different conditions of concentration and applied voltage. An electric field was applied uniformly throughout the system to all mobile atoms. On average, the resultant net electric field falls primarily across the membrane channel, as expected for two conductive baths separated by a membrane capacitance. The channel is rarely occupied by more than one ion. Current-voltage relations are concentration dependent and superlinear at high concentrations.

Computer Simulation↗
PubMed2002

Electromagnetic fields for bone healing.

Electrical stimulation has been applied in a number of different ways to influence tissue healing. Most of the early work was carried out by orthopedic surgeons looking for new ways of enhancing fracture healing, particularly those fractures that had developed into nonunions. Electrical energy can be supplied to a fracture by direct application of electrodes or inducing current by use of pulsed electromagnetic field or capacitive coupling. Many of these techniques have not been standardized, so interpretation of the literature can be difficult and misleading. Despite this, there have been a few good laboratory and clinical studies to investigate the effect of electrical stimulation on fracture healing, which are reviewed. These do not permit recommendation or rejection of the technique per se; however, there is some room for optimism. The authors present some of the guidelines for using this treatment modality but suggest that all treatment should be carried out as part of a clinical trial in order to generate reliable data.

Journal Article↗
PubMed1982

Contractile and electrical characteristics of extensor muscle from alloxan-diabetic rats. An in vitro study.

Diabetes mellitus was produced by withholding insulin from female rats previously treated with alloxan. In vitro studies of contractile and electrical properties of the extensor digitorum longus muscle were analyzed at various periods following cessation of insulin treatment. In severely diabetic ketoacidotic rat muscles it was observed that both direct and indirectly induced twitch and tetanic tensions were significantly reduced to the same degree. Resting membrane potentials were significantly reduced but repolarized when external chloride was removed. Indirectly induced action potential amplitude and rate of depolarization were significantly depressed and there was a significant increase in action potential duration. Specific membrane in action potential duration. Specific membrane resistance decreased significantly but transiently due largely to an increase in chloride conductance and specific capacitance increased significantly. After extended periods of milder diabetes, specific tetanic tension decreased slightly while specific twitch tension was unchanged in both direct and indirectly induced contractions. Resting potentials were only slightly reduced. Indirectly elicited action potential amplitude and rate of depolarization were slightly reduced. Specific membrane resistance was significantly increased largely due to decreases in chloride conductance. Specific capacitance was unchanged.

Action Potentials↗
PubMed1993

Hypotonically induced changes in the plasma membrane of cultured mammalian cells.

Cells from three cell lines were electrorotated in media of osmotic strengths from 330 mOsm to 60 mOsm. From the field-frequency dependence of the rotation speed, the passive electrical properties of the surfaces were deduced. In all cases, the area-specific membrane capacitance (Cm) decreased with osmolality. At 280 mOsm (iso-osmotic), SP2 (mouse myeloma) and G8 (hybridoma) cells had Cm values of 1.01 +/- 0.04 microF/cm2 and 1.09 +/- 0.03 microF/cm2, respectively, whereas dispase-treated L-cells (sarcoma fibroblasts) exhibited Cm = 2.18 +/- 0.10 microF/cm2. As the osmolality was reduced, the Cm reached a well-defined minimum at 150 mOsm (SP2) or 180 mOsm (G8). Further reduction in osmolality gave a 7% increase in Cm, after which a plateau close to 0.80 microF/cm2 was reached. However, the whole-cell capacities increased about twofold from 200 mOsm to 60 mOsm. L-cells showed very little change in Cm between 280 mOsm and 150 mOsm, but below 150 mOsm the Cm decreased rapidly. The changes in Cm correlate well with the swelling of the cells assessed by means of van't Hoff plots. The apparent membrane conductance (including the effect of surface conductance) decreased with Cm, but then increased again instead of exhibiting a plateau. The rotation speed of the cells increased as the osmolality was lowered, and eventually attained almost the theoretical value. All measurements indicate that hypo-osmotically stressed cells obtain the necessary membrane area by using material from microvilli. However, below about 200 mOsm the whole-cell capacities indicate the progressive incorporation of "extra" membrane into the cell surface.

Animals↗
PubMed2006

Descending vasa recta endothelium is an electrical syncytium.

We examined gap junction coupling of descending vasa recta (DVR). DVR endothelial cells or pericytes were depolarized to record the associated capacitance transients. Virtually all endothelia and some pericytes exhibited prolonged transients lasting 10-30 ms. Carbenoxolone (100 microM) and 18beta-glycyrrhetinic acid (18betaGRA; 100 microM) markedly shortened the endothelial transients. Carbenoxolone and heptanol (2 mM) reduced the pericyte capacitance transients when they were prolonged. Lucifer yellow (LY; 2 mM) was dialyzed into the cytoplasm of endothelial cells and pericytes. LY spread diffusely along the endothelial monolayer, whereas in most pericytes, it was confined to a single cell. In some pericytes, complex patterns of LY spreading were observed. DVR cells were depolarized by voltage clamp as fluorescence of bis(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)] was monitored approximately 200 microm away. A 40-mV endothelial depolarization was accompanied by a 26.1 +/- 5.5-mV change in DiBAC(4)(3) fluorescence. DiBAC(4)(3) fluorescence did not change after 18betaGRA or when pericytes were depolarized. Similarly, propagated cytoplasmic Ca(2+) responses arising from mechanical perturbation of the DVR wall were attenuated by 18betaGRA or heptanol. Connexin (Cx) immunostaining showed predominant linear Cx40 and Cx43 in endothelia, whereas Cx37 stained smooth muscle actin-positive pericytes. We conclude that the DVR endothelium is an electrical syncytium and that gap junction coupling in DVR pericytes exists but is less pronounced.

Animals↗
PubMed2003

Control of secretion by temporal patterns of action potentials in adrenal chromaffin cells.

Action potentials (APs) are the principal physiological stimuli for neurotransmitter secretion in neurons. Most studies on stimulus-secretion coupling have been performed under voltage clamp using artificial electrical stimuli. To investigate the modulatory effects of AP codes on neural secretion, we introduce a capacitance method to study AP-induced secretion in single cells. The action potential pattern was defined by a four-parameter "code function:" F(n, m, f, d). With this method, cell secretion evoked by stimulation with an AP code was quantified in real time by membrane capacitance (Cm) in adrenal chromaffin cells. We found, in addition to AP frequency (f), for a given number of APs, another parameter of the AP code, the number of AP bursts (m) in which the set of APs occurs, can effectively modulate cell secretion. Possible mechanisms of the m effect are depletion of the readily releasable pool and inactivation of Ca2+ channels during a burst of APs. The physiological m effect may play a key role in AP-mediated neural information transfer within a single neuron and among the elements of a neural network.

Action Potentials↗
PubMed1989

Conformational transitions and change translocation by the Na,K pump: comparison of optical and electrical transients elicited by ATP-concentration jumps.

The electrogenic properties of the Na,K-ATPase were studied by correlating transient electrical events in the pump molecule with conformational transitions elicited by an ATP-concentration jump. Flat membrane fragments containing a high density (approximately 8000 microm(-2)) of oriented Na,K-ATPase molecules were bound to a planar lipid bilayer acting as a capacitive electrode. ATP was released in the medium from a photolabile inactive ATP derivative ("caged" ATP) by a 40-microsec light flash. Electrical signals resulting from transient charge movements in the protein under single-turnover conditions were recorded in the external measuring circuit. In parallel experiments carried out under virtually identical conditions, the fluorescence of membrane fragments containing Na,K-ATPase with covalently-bound 5-iodoacetamido-fluorescein (5-IAF) was monitored after the ATP-concentration jump. When the medium contained Na+, but no K+, the fluorescence of the 5-IAF-labeled protein decreases monotonously after release of ATP. In the experiments with membrane fragments bound to a planar bilayer, a transient pump current was observed which exhibited virtually the same time behavior as the fluorescence decay. This indicates that optical and electrical transients are governed by the same rate-limiting reaction step. Experiments with chymotrypsin-modified Na,K-ATPase suggest that both the fluorescence change as well as the charge movement are associated with the deocclusion of Na+ and release to the extracellular side. In experiments with Na+-free K+ media, a large inverse fluorescence change is observed after the ATP-concentration jump, but no charge translocation can be detected. This indicates that deocclusion of K+ is an electrically silent process.

Animals↗