mV Voltage Research Articles

A biodegradable electrical bioconductor made of polypyrrole nanoparticle/poly(D,L-lactide) composite: A preliminary in vitro biostability study.

The electrical stability of a novel polypyrrole (PPy)/poly(D,L-lactide) (PDLLA) composite was studied in vitro and compared with that of PPy-coated polyester fabrics. Specimens were incubated in Ringer's solution at 37 degrees C for up to 8 weeks with or without the circulation of DC current under a constant 100 mV voltage. In situ current variation with incubation time was recorded. The AC volume electrical conductivity of the specimens before and after incubation in phosphate-buffered saline was recorded using a frequency analyzer. Water absorption and weight loss were monitored metrologically. Changes in the oxidation state of incubated PPy were analyzed with X-ray photoelectron spectroscopy. The morphological changes were observed with scanning electron microscopy, and the glass transition temperature of the PDLLA was investigated using differential scanning calorimetry. The PPy/PDLLA composite in Ringer's solution sustained a relatively stable conductivity up to 8 weeks after an initial period of "conditioning." The PPy-coated fabrics experienced a rapid loss of conductivity when subjected to electrical circulation and regained part of it when disconnected. The volume conductivity of the nonincubated PPy/PDLLA membrane behaved as a typical conductor in the low-frequency range. The mechanisms involved in the various electrical behaviours of the PPy/PDLLA composite and PPy-coated fabrics are discussed. In conclusion, the PPy/PDLLA composite was able to deliver a biologically significant electrical current in a simulated biological solution for up to 8 weeks and therefore may be considered as a first-generation synthetic biodegradable bioconductor.

Thermal stability of atomic-layer-deposited HfO2 thin films on the SiNx-passivated Si substrate

HfO 2 thin films were deposited on SiNx-passivated Si wafers at 300 and 400 °C using an atomic-layer-deposition technique. The SiNx films were deposited by another atomic-layer-deposition process at 595 °C. The SiNx films worked well as barriers to both Si and O diffusion, resulting in a small decrease in the capacitance density even after post-annealing at temperatures up to 1000 °C, compared either to the HfO2 film deposited directly on Si or an Al2O3-barrier-layer/Si substrate. The decrease in the capacitance density after post-annealing, although relatively small, was due to Hf and O diffusion into the interface layer. Interestingly, post-annealing under an atmosphere containing small amount of oxygen (∼1%) decreased the capacitance density to a smaller degree. However, the interface and bulk capturing of the carrier was serious, resulting in a rather large hysteresis (∼100 mV) voltage in the capacitance–voltage measurements even after post-annealing.

Low threshold T-type calcium current in rat embryonic chromaffin cells.

1. The gating kinetics and functions of low threshold T-type current in cultured chromaffin cells from rats of 19-20 days gestation (E19-E20) were studied using the patch clamp technique. Exocytosis induced by calcium currents was monitored by the measurement of membrane capacitance and amperometry with a carbon fibre sensor. 2. In cells cultured for 1-4 days, the embryonic chromaffin cells were immunohistochemically identified by using polyclonal antibodies against dopamine beta-hydroxylase (DBH) and syntaxin. The immuno-positive cells could be separated into three types, based on the recorded calcium current properties. Type I cells showed exclusively large low threshold T-type current, Type II cells showed only high voltage activated (HVA) calcium channel current and Type III cells showed both T-type and HVA currents. These cells represented 44 %, 46 % and 10 % of the total, respectively. 3. T-type current recorded in Type I cells became detectable at -50 mV, reached its maximum amplitude of 6.8 +/- 1.2 pA pF(-1) (n = 5) at -10 mV and reversed around +50 mV. The current was characterized by criss-crossing kinetics within the -50 to -30 mV voltage range and a slow deactivation (deactivation time constant, tau(d) = 2 ms at -80 mV). The channel closing and inactivation process included both voltage-dependent and voltage-independent steps. The antihypertensive drug mibefradil (200 nM) reduced the current amplitude to about 65 % of control values. Ni(2+) also blocked the current in a dose-dependent manner with an IC(50) of 25 microM. 4. T-type current in Type I cells did not induce exocytosis, while catecholamine secretion by exocytosis could be induced by HVA calcium current in both Type II and Type III cells. The failure to induce exocytosis by T-type current in Type I cells was not due to insufficient Ca(2+) influx through the T-type calcium channel. 5. We suggest that T-type current is expressed in developing immature chromaffin cells. The T-type current is replaced progressively by HVA calcium current during pre- and post-natal development accompanying the functional maturation of the exocytosis mechanism.

Component development for a 16 Gb/s RSFQ-CMOS interface system

We have been developing an RSFQ-CMOS interface system. The system consists of three modules: a 1 to 32 bit DDST demultiplexer which converts a 16 Gb/s SFQ data input into a 32-channel 500 Mb/s output, asynchronous stacked-SQUID amplifiers which amplify an SFQ data input into a 5 mV voltage level output, and 77 K CMOS amplifiers which amplify a 5 mV voltage level input into a 5 V output at 500 MHz. We have implemented the asynchronous stacked-SQUID amplifier and the 77 K CMOS amplifier using the HYPRES 1 kA/cm/sup 2/ Nb process and the ROHM 0.6 /spl mu/m CMOS process, respectively. It was demonstrated that the 24-stage asynchronous stacked-SQUID amplifier amplifies an SFQ data input into a 2.0 mV voltage level at 600 MHz. The 77 K CMOS amplifier was shown to amplify a 5 mV voltage level input into 5 V at 500 MHz from the simulation, and a 175 mV voltage input into 3.5 V at 90 MHz from the experiment.

Investigation of an InGaP/GaAs resonant-tunneling heterojunction bipolar transistor

An interesting InGaP/GaAs resonant-tunneling heterojunction bipolar transistor incorporating a superlattice (SL) structure in the emitter has been fabricated and studied. With the n-type doped well, the strongly coupling effect dominating the biased SL behaves like a double barrier operation. On the basis of the transfer matrix method, the transport mechanism of sequential miniband conduction can be developed by the theoretical calculation associated with the RT in the studied SL structure. Experimentally, the double negative differential resistance phenomena are presented both in the two-and three-terminal current–voltage characteristics at 300 K. In addition, excellent transistor behaviors including the high dc current gain as high as 70, low saturation voltage smaller than 1.2 V, low offset voltage of 110 mV and high breakdown voltage larger than 20 V are obtained.

Fabrication of Screen-Printed Carbon Electrode Arrays for Sensing Neuronal Messengers

Deciphering the methods of communication between neurons and ensembles of neurons in the brain is a major area of interest in the field of neuroscience. An array of sensors designed to sense specific neuronal messengers or neurotransmitters should provide a better method to study their spatial and temporal activity across a tissue. Screen-printing is a simple and inexpensive technique for fabricating arrays of sensors that can be used to monitor neurotransmitter activity in the brain. One important neuronal messenger known to actively modulate neuronal excitability is nitric oxide (NO). Carbon has been shown to interact with NO in an oxidation-reduction reaction that produces a current proportional to the amount of NO present. The proposed design uses carbon polymer inks screen printed onto aluminum traces to form the sensors. A thick, photodefineable epoxy resin, known as SU-8, serves as an insulator and a mold for the carbon ink. A potentiostat is used to apply a 900 mV voltage between the carbon sensor and a reference electrode positioned in the bath of the experimental setup. The current produced indicates the concentration of NO in close proximity to the carbon site. The screen-printing technique provides an elegant way to produce an array of individual carbon sensors. The carbon sensor array promises a novel approach to mapping the distribution of neurotransmitters in brain tissue.

Cell volume-sensitive sodium channels upregulated by glucocorticoids in U937 macrophages.

Glucocorticoids exert their anti-inflammatory action in part by influencing macrophages. As regulation of macrophage function involves ion channels, the present study was performed to elucidate the influence of glucocorticoids on macrophage ion channel activity. To this end, the effects of corticosteroids on the sodium conductance in human monocytic cells (U937) was studied using whole-cell and outside-out patch-clamp techniques. Increasing extracellular osmolarity from 310 to 420 mosmol/kg led to cell shrinkage followed by marked activation of inward whole-cell current from -36+/-2 to -72+/-9 pA (n=13; recorded at -150 mV voltage with CsCl intracellular solution, NaCl extracellular solution) while outward current remained unchanged. The increase of inward current was accompanied by a positive shift of reversal potential and was sensitive to amiloride (100 microM). The activation of inward current by shrinkage was not observed when external sodium was replaced by potassium, indicating that the shrinkage-stimulated conductance is sodium selective. Outside-out single-channel measurements revealed a unitary conductance of 6+/-1 pS (n=5) for the sodium-selective amiloride-sensitive current. Pretreating the cells with deoxycorticosterone (100 nM/6 h) markedly upregulated the shrinkage-activated Na+ current. In conclusion, human macrophage-like U937 cells express a sodium-selective shrinkage-activated channel which is upregulated by corticosteroids. Activation of the channel may increase cell volume, an effect of glucocorticoids in other cells.

SUPERCONDUCTING-RESISTIVE-TRANSITION DEVICE FOR THE PRECISION MEASUREMENT OF LOW AC VOLTAGE

Single and multijunctions thermal converters are devices widely utilized for AC measurements at room temperature. However, low sensitivity and high noise of these devices limits their applications at voltage level above 10 mV. A cryogenic thermal transfer sensor has been developed to realise AC measurements at 1 mV voltage level. This device consists of a superconducting-resistive-transition Nb thin film, which detects the AC power, dissipated on a Cr film resistor. To improve the sensitivity, the sensor has been fabricated on a 500 nm thick square silicon nitride membrane with size ranging from 1 × 1 mm 2 to 3.5 × 3.5 mm 2. The device has been tested at liquid helium and a thermal conductance lower than 10-6 W/K has been measured. From these data we expect an increasing of responsivity higher than three order of magnitude and a noise limited by intrinsic thermal noise.

Apical nonspecific cation channels in everted collecting tubules of potassium-adapted ambystoma.

We observed intermediate conductance channels in approximately 20% of successful patch-clamp seals made on collecting tubules dissected from Ambystoma adapted to 50 mm potassium. These channels were rarely observed in collecting tubules taken from animals which were maintained in tap water. Potassium-adaptation either leads to an increase in the number of channels present or activates quiescent channels. In cell-attached patches the conductance averaged 30.3 +/- 2.4 (9) pS. Since replacement of the chloride in the patch pipette with gluconate did not change the conductance, the channel carries cations, not anions. Notably, channel activity was observed at both positive and negative pipette voltages. When the pipette was voltage clamped at 0 mV or positive voltages, the current was directed inward, consistent with the movement of sodium into the cell. The pipette voltage at which the polarity of the current reversed (movement of potassium into the pipette) was -29.6 +/- 6.5(9) mV. Open probability at 0 mV pipette voltage was 0.08 +/- 0.03 and was unaffected when the apical membrane was exposed to either 2 x 10(-6) or 2 x 10(-5) m of amiloride. Exposure of the basolateral surface of the tubule to a saline containing 15 mm potassium caused a significant increase (P less than 0.001) in the open probability of these channels to 0.139 +/- 0.002 without affecting the conductance of the apical channel. These data illustrate the presence of an intermediate conductance, poorly selective, amiloride-insensitive cation channel in native vertebrate collecting tubule. We postulate that, at least in amphibia, this channel may be used to secrete potassium.

An altered repolarizing potassium current in rat cardiac myocytes after subtotal nephrectomy.

Renal failure in humans is associated with electrocardiographic changes including altered QT interval dispersion, which suggests that cardiac myocyte repolarization is abnormal and which appears to correlate with cardiac prognosis. In this study, cardiac myocyte repolarizing currents have been studied in isolated cells from rats 8 wk after subtotal nephrectomy (SNx), using sham-operated animals as controls. In addition, monophasic cardiac action potentials were recorded from the epicardial surface of the left ventricle (LV) apex, LV base, and the right ventricle of isolated perfused hearts paced at 320/min. SNx was associated with cardiac hypertrophy and histologic evidence of myocardial fibrosis, but SNx rats were not hypertensive. Repolarizing K(+) currents were measured using whole-cell patch-clamp, and 4-aminopyridine (4-AP)-sensitive transient outward (I(to)) and 4-AP-insensitive sustained outward (I(so)) components were quantified. After SNx, I(to) was increased by two to threefold at voltages from -30 to +60 mV and showed increased heterogeneity. For example, at 0 mV voltage clamp pulse, the median I(to) was increased from 3.23 pA/pF in control myocytes (interquartile range 3.20 pA/pF, n = 24) to 5.86 pA/pF in SNx myocytes (interquartile range 7.32 pA/pF, n = 21, P: < 0.005). The kinetics of inactivation of I(to) were altered after SNx with slowing both of the onset and the recovery from inactivation. The mean time constant of inactivation at +30 mV after SNx was 14.2 +/- 1.6 ms (n = 20) compared with control values of 9.8 +/- 0.6 ms (n = 23, P: < 0.05). Neither I(so) nor inward rectifier K(+) currents were altered after SNx. The action potential duration (APD(50)) at the left ventricular base was approximately 20% shorter (P: < 0.02) in hearts from SNx rats compared with controls. 4-AP (2 mM) prolonged the APD(50) in all regions in hearts from both SNx and control rats and abolished the APD(50) shortening in SNx. These results indicate that abnormalities of the cardiac transient outward K(+) current contribute to alterations in the cardiac action potential in renal failure and warrant further investigation because they may contribute to altered repolarization and arrythmogenesis.

Major potassium conductance in type I hair cells from rat semicircular canals: characterization and modulation by nitric oxide.

Mammalian vestibular organs have two types of hair cell, type I and type II, which differ morphologically and electrophysiologically. Type I hair cells alone express an outwardly rectifying current, I(K, L), which activates at relatively negative voltages. We used whole cell and patch configurations to study I(K,L) in hair cells isolated from the sensory epithelia of rat semicircular canals. I(K,L) was potassium selective, blocked by 4-aminopyridine, and permeable to internal cesium. It activated with sigmoidal kinetics and was half-maximally activated at -74.5 +/- 1.6 mV (n = 35; range -91 to -50 mV). It was a very large conductance (91 +/- 8 nS at -37 mV; 35 nS/pF for a cell of average size). Patch recordings from type I cells revealed a candidate ion channel with a conductance of 20-30 pS. Because I(K,L) was activated at the resting potential, the cells had low input resistances (R(m)): median 25 MOmega at -67 mV versus 1.3 GOmega for type II cells. Consequently, injected currents comparable to large transduction currents (300 pA) evoked small (</=10 mV) voltage responses. The cells' small voltage responses and negative resting potentials (V(R) = -81.3 +/- 0.2 mV, n = 144) pose a problem for afferent neurotransmission: how does the receptor potential depolarize the cell into the activation range of Ca(2+) channels (positive to -60 mV) that mediate transmitter release? One possibility, suggested by spontaneous positive shifts in the activation range of I(K,L) during whole cell recording, is that the activation range might be modulated in vivo. Any factor that reduces the number of I(K,L) channels open at V(R) will increase R(m) and depolarize V(R). Nitric oxide (NO) is an ion channel modulator that is present in vestibular epithelia. Four different NO donors, applied externally, inhibited the I(K,L) conductance at -67 mV, with mean effects ranging from 33 to 76%. The NO donor sodium nitroprusside inhibited channel activity in patches when they were cell-attached but not excised, suggesting an intracellular cascade. Consistent with an NO-cGMP cascade, 8-bromo-cGMP also inhibited whole cell I(K,L). Ca(2+)-dependent NO synthase is reported to be in hair cells and nerve terminals in the vestibular epithelium. Excitatory input to vestibular organs may lead, through Ca(2+) influx, to NO production and inhibition of I(K,L). The resulting increase in R(m) would augment the receptor potential, a form of positive feedback.

Very negative potential for half-inactivation of, and effects of anions on, voltage-dependent sodium currents in acutely isolated rat olfactory receptor neurons.

Previous measurements with CsF pipette solutions using whole-cell patch-clamp techniques in dissociated rat olfactory receptor neurons (ORNs) indicated that the sodium currents had very negative inactivation characteristics with the implication that the cell resting potential must also normally have a very negative value. This study supports the conclusions that such an effect was real and not dependent on either the nature of the pipette anions or the recording situation previously used. For all pipette solutions, sodium currents showed a threshold activation approximately -80 mV and half-maximal activation voltages approximately -55 with half-inactivation potential < or =-100 mV, without being significantly affected by the replacement of F(-) by other pipette anions (H(2)PO(-)(4) and acetate(-)) or the addition of nucleotides and glutathione (which did cause a very slight positive shift). F(-), followed by H(2)PO(-)(4) and to a much lesser extent by acetate(-), was the most favorable pipette anion for obtaining good seals and whole-cell sodium currents in these extremely small ORNs. These results implied that resting potentials, for viable responsive cells, should be more negative than about -90 mV, as supported by the observation that action potentials could only be evoked from holding potentials more negative than -90 mV.

Resting potential of excitable neuroblastoma cells in weak magnetic fields.

The mechanism by which static and low-frequency magnetic fields are transduced into biological signals responsible for reported effects on brain electrical activity is not yet ascertained. To test the hypothesis that fields can cause a subthreshold change in the resting membrane potential of excitable cells, we measured changes in transmembrane current under voltage clamp produced in SH-SY5Y neuroblastoma cells, using the patch-clamp method in the whole-cell configuration. In separate experiments, cells were exposed to static fields of 1, 5, and 75 G, to time-varying fields of 1 and 5 G, and to combined static and time-varying fields tuned for resonance of Na+, K+, Ca2+, or H+. To increase sensitivity, measurements were made on cells connected by gap junctions. For each cell, the effect of the field was evaluated on the basis of 100 trials consisting of a 5-s exposure immediately followed by a 5-s control period. In each experiment, the field had no discernible effect on the transmembrane current in the vicinity of zero current (- 50 mV voltage clamp). The sensitivity of the measuring system was such that we would have detected a current corresponding to a change in membrane potential as small as 38 microV. Consequently, if sensitivity of mammalian cells to magnetic fields is mediated by subthreshold changes in membrane potential, as in sensory transduction of sound, light, and other stimuli, then the ion channels responsible for the putative changes are probably present only in specialized sensory neurons or neuroepithelial cells. A change in transmembrane potential in response to magnetic fields is not a general property of excitable cells in culture.

A distributed selector IC using GaAs MESFET's with multilayer-interconnection structure

This paper describes novel high-speed selector circuits based on the distributed circuit approach and their circuit design methodologies. Two types of distributed selectors are designed and fabricated using 0.16 /spl mu/m GaAs MESFET's with multilayer-interconnection structure. Both basically consist of eight stages of series-gated source-coupled field-effect transistor (FET) logic (SCFL) selector cell units laid out in a distributed fashion. The second circuit incorporates additional functions: a data input level shifter in each cell to make an SCFL interface for the data input and a balun for single-balance transformation of the clock input. A small-signal distributed amplifier design is extended to a large-signal distributed logic IC design, taking dynamic variations in transistor parameters into consideration. The error-free operation of both fabricated distributed selector IC's is confirmed at up to 40 Gbit/s, and the first IC still exhibited eye opening with 130 mV voltage swing of the inside measurement at 70 Gbit/s, which reaches 80% of f/sub T/ of the fabricated FET. These distributed selector IC's successfully exhibit eye opening at higher bit rates compared to the conventional lumped-element design selector.

Electrochemical studies of a truncated laccase produced in Pichia pastoris.

The cDNA that encodes an isoform of laccase from Trametes versicolor (LCCI), as well as a truncated version (LCCIa), was subcloned and expressed by using the yeast Pichia pastoris as the heterologous host. The amino acid sequence of LCCIa is identical to that of LCCI except that the final 11 amino acids at the C terminus of LCCI are replaced with a single cysteine residue. This modification was introduced for the purpose of improving the kinetics of electron transfer between an electrode and the copper-containing active site of laccase. The two laccases (LCCI and LCCIa) are compared in terms of their relative activity with two substrates that have different redox potentials. Results from electrochemical studies on solutions containing LCCI and LCCIa indicate that the redox potential of the active site of LCCIa is shifted to more negative values (411 mV versus normal hydrogen electrode voltage) than that found in other fungal laccases. In addition, replacing the 11 codons at the C terminus of the laccase gene with a single cysteine codon (i.e., LCCI-->LCCIa) influences the rate of heterogeneous electron transfer between an electrode and the copper-containing active site (k(het) for LCCIa = 1.3 x 10(-4) cm s(-1)). These results demonstrate for the first time that the rate of electron transfer between an oxidoreductase and an electrode can be enhanced by changes to the primary structure of a protein via site-directed mutagenesis.

Elevation of basolateral K+ induces K+ secretion by apical maxi K+ channels in Ambystoma collecting tubule.

We previously reported that exposure of aquatic-phase Ambystoma tigrinum to a solution containing 50 mM K+ (K+ adaptation) caused a nearly 10-fold increase in the number of detectable maxi K+ channels on the apical membrane of their initial collecting tubules. In apparent contradiction to the notion that maxi K+ channels contribute to K+ secretion, these channels were not routinely active at the resting membrane potential (0 mV voltage clamp). To test the possibility that hyperkalemia yields maxi K+ channels that are secreting K+ (i.e., active at 0 mV), we patch-clamped the apical membranes of initial collecting tubules under conditions of elevated basolateral K+ (15 mM). Seven patches containing maxi K+ channels were studied. Six of the seven patches showed maxi K+ channel activity when voltage was clamped at 0 mV. Open probability and unitary current averaged 0.059 +/- 0.016 and 1.65 +/- 0.50 pA, respectively. This activity, together with the high density of channels observed (1.06 channels/micrometer2), indicates that after K+ adaptation, maxi K+ channels contribute to the ability of the late distal nephron of amphibians to secrete K+.

A damage mechanism: lightning-initiated fault-current arcs to communication cables buried beneath overhead electric power lines

A lightning strike to an energised overhead conductor of an electric power line is dangerous; the lightning impulse will establish a conductive path across the power-line insulator, down the pole, and through the soil to any buried utility line. In a significant number of cases, this conductive path will allow the establishment of a large, long-duration power fault current from the lightning-struck power conductor to the buried utility line. This power arc will terminate on the grounded pipe or cable shield, causing rupture and failure. The existence of this damage mechanism was confirmed in the laboratory with a full-scale mock-up of a utility right-of-way. The phenomenon of lightning-triggered arc establishment through soil was then examined more closely with a high-resolution apparatus in which most parameters could be tightly controlled. Artificial lightning impulses from 0.3 to 2.8 MV and 60-Hz power-line voltages from 6.24 to 15.71 kV were used. Soil condition, electrode spacing, power-line voltage, lightning impulse voltage, and geometry were found to govern the probability of a lightning-initiated fault current arc through the soil in a predictable manner. For soil of 500 000-/spl Omega//spl middot/cm resistivity, the distance between a simulated power system lightning ground and a buried cable at which a fault current arc is not initiated was found to be about 40 cm. This safe distance was proportional to the geometric mean of the power-line voltage and the peak lightning impulse voltage.

Blockade by 18beta-glycyrrhetinic acid of intercellular electrical coupling in guinea-pig arterioles.

1. Intercellular electrical communication between smooth muscle and endothelial cells was examined in guinea-pig mesenteric arterioles using the whole-cell patch-clamp method. The time course of the current required to impose a 10 mV voltage clamp step was used to determine the extent of electrical coupling between them. Currents recorded from both smooth muscle and endothelial cells relaxed in a multi-exponential manner, indicating the existence of electrical coupling between cells. 2. 18beta-Glycyrrhetinic acid, a gap junction blocker, quickly blocked electrical communication at 40 microM, while neither heptanol nor octanol did so at concentrations of up to 1 mM. 3. In the current clamp mode, repetitive spikes, induced by 10 mM Ba2+ solutions, could be recorded from both kinds of cells. After blocking gap junctions, spikes could only be recorded from the smooth muscle cell layer, indicating that they had been conducted through myoendothelial junctions. 4. In endothelial cells, acetylcholine (ACh, 3 microM) induced hyperpolarizing responses, which had two phases (an initial fast and a second slower phase) in the current clamp condition. This ACh response persisted in the presence of 18beta-glycyrrhetinic acid, although this compound seemed to make the membrane slightly leaky. 5. After blocking gap junctions, the membrane potential of a single cell in a multicellular preparation could be well clamped. Thus, 18beta-glycyrrhetinic acid may be useful in studying the function of both arteriolar smooth muscle and endothelial cells while they remain located within a multicellular preparation.

Impedance of goat eye lens at different DC voltages.

A computer assisted AC impedance system is used to measure the DC voltage-current (V-I) characteristics and AC impedance of a goat eye lens using a two-probe Ag-AgCl electrode system. The measurement of the V-I characteristics shows that when a DC voltage from 0 mV to 30 mV is applied, the resultant current decreases from an initial value of 0.58 microA to 0.006 microA. However, when the voltage is increases beyond 30 mV, the current increases and reaches a value of 0.9 microA at 100 mV. The data on the frequency response (0.01-10 Hz) of the impedance of lens tissue show an inverse relationship with frequency. The effect of various DC voltages, namely 0, 30, 50, 100 and 200 mV, on the impedance of the eye lens is also investigated over a frequency range of 0.01-10 Hz. The measurement results for both V-I characteristics and AC impedance further suggest the presence of a 30 mV voltage compartment in the goat eye lens.

The Reduction in Electroporation Voltages by the Addition of a Surfactant to Planar Lipid Bilayers

The effects of a nonionic surfactant, octaethyleneglycol mono n-dodecyl ether (C 12E 8), on the electroporation of planar bilayer lipid membranes made of the synthetic lipid 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), was studied. High-amplitude (∼100–450 mV) rectangular voltage pulses were used to electroporate the bilayers, followed by a prolonged, low-amplitude (∼65 mV) voltage clamp to monitor the ensuing changes in transmembrane conductance. The electroporation thresholds of the membranes were found for rectangular voltage pulses of given durations. The strength-duration relationship was determined over a range from 10 μs to 10 s. The addition of C 12E 8 at concentrations of 0.1, 1, and 10 μM to the bath surrounding the membranes decreased the electroporation threshold monotonically with concentration for all durations ( p < 0.0001). The decrease from control values ranged from 10% to 40%, depending on surfactant concentration and pulse duration. For a 10- μs pulse, the transmembrane conductance 150 μs after electroporation ( G 150) increased monotonically with the surfactant concentration ( p = 0.007 for 10 μM C 12E 8). These findings suggest that C 12E 8 incorporates into POPC bilayers, allowing electroporation at lower intensities and/or shorter durations, and demonstrate that surfactants can be used to manipulate the electroporation threshold of lipid bilayers.