Novel Brugada syndrome‐causing mutation in ion‐conducting pore of cardiac Na+ channel does not affect ion selectivity properties

Aim: Brugada syndrome is an inherited cardiac disease with an increased risk of sudden cardiac death. Thus far Brugada syndrome has been linked only to mutations in SCN5A, the gene encoding the α‐subunit of cardiac Na⁺ channel. In this study, a novel SCN5A gene mutation (D1714G) is reported, which has been found in a 57‐year‐old male patient. Since the mutation is located in a segment of the ion‐conducting pore of the cardiac Na⁺ channel, which putatively determines ion selectivity, it may affect ion selectivity properties. Methods: HEK‐293 cells were transfected with wild‐type (WT) or D1714G α‐subunit and β‐subunit cDNA. Whole‐cell configuration of the patch‐clamp technique was used to study biophysical properties at room temperature (21 °C) and physiological temperature (36 °C). This study represents the first measurements of human Na⁺ channel kinetics at 36 °C. Ion selectivity, current density, and gating properties of WT and D1714G channel were studied. Results: D1714G channel yielded nearly 80% reduction of Na⁺ current density at 21 and 36 °C. At both temperatures, no significant changes were observed in V_1/2 values and slope factors for voltage‐dependent activation and inactivation. At 36 °C, but not at 21 °C, D1714G channel exhibited more slow inactivation compared with WT channel. Ion selectivity properties were not affected by the mutation at both temperatures, as assessed by either current or permeability ratio. Conclusion: This study shows no changes in ion selectivity properties of D1714G channel. However, the profoundly decreased current density associated with the D1714G mutation may explain the Brugada syndrome phenotype in our patient.     

Nuclear magnetic resonance studies on polymer carbanions, 5. Polystyryl carbanion with lithium as counter cation and its dimer model compounds

Oligostyryllithium was synthesized by the reaction of sec-butyllithium with styrene in diethyl ether at ?40°C. Dimer model anions (counter cations: Li and K) of the growing chain ends were synthesized by metallation of 1-methoxy-1,3-diphenylpropane. The structures of the lithium compounds were corroborated by ¹³C NMR spectroscopy and compared with those of the potassium compounds. As for polystyryllithium and its model compounds, the charge density on the α-carbon increased and that on the phenyl ring of the growing end decreased with increasing molecular weight, while, in polystyrylpotassium and its model compounds, the charge density on the α-carbon increased and the one on the phenyl ring did not change with increasing molecular weight. The temperature change of the ¹H NMR spectrum of oligostyryllithium in diethyl ether indicated rotation around the C-1? C_α bond at lower temperatures than in tetrahydrofuran, but the activation energy was the same in both solvents. T₁ values of the phenyl carbons in model compound 2b were one to two orders of magnitude shorter than those of the protonated compound.     

Molecular characterization of water-soluble,cationic polyelectrolytes

Poly{acrylamide-co-[2-(acryloyloxy)ethyltrimethylammonium chloride]} (1) , Poly{acrylamide-co-[2-(methacryloyloxy)ethyltrimethylammonium chloride]} (2) and Poly{acrylamide-co-[3-(acryloylamino)propyltrimethylammonium chloride]} (3) with cationic monomeric unit mole fractions of 8, 25, and 50 mol-%, and the corresponding homopolymers were characterized with respect to their molecular dimensions in 1 M sodium chloride solution at 25°C in the molecular weight range from 200000 to 16000000, using light-scattering and viscometric measurements. It was possible to establish correlations between molecular weight, intrinsic viscosity and radius of gyration. Whereas a steady increase in the exponents of the [η] vs. M- and 〈R²_G〉^0,5 vs. M-relationships can be observed with increasing charge density, there is an initial decrease in the values of the exponents for 2 and 3 , when 8 mol-% of the cationic monomer is inserted into poly-acrylamide. If the charge density is increased further, these values can also be seen to rise steadily. The findings are explained by the different structures in solution, which are formed by the copolymers and homopolymers investigated due to their chemical structure. The radii of gyration were calculated from the intrinsic viscosities with the aid of the Flory-Fox equation. However, neither the results obtained with the Flory-Fox constant Φ₀= 3,69. 10²⁴ mol^?1, nor those with the value of Φ₀= 2,10. 10²⁴ mol^?1 showed good agreement with the experimentally recorded data.     

Charge density of renal interstitium

The charge density of renal interstitium was analysed from the volume of distribution of negative native albumin as compared with neutralized albumin, labelled with ¹²⁵I and ¹³¹ I, respectively. The experiments were conducted by infusing the two probes intravenously at a rate which kept the plasma concentrations stable. The concentration in renal hilar lymph, C_lymph(t), will then obey the function C_lymph(t) = C_lymph(t_x) (1-exp—Kt), where C_lymph(t_x) is the steady state Concentration and K the time constant for passage of the tracer through the renal interstitium - the former is dependent on the permeability of the peritubular capillary membrane, whereas the time constant is inversely related to the interstitial distribution volume of the tracers. The lymph-to-plasma concentration ratio (L/P-ratio) of negative, native albumin was found to be lower than that of neutralized albumin, a finding suggesting that the peritubular capillary membrane is negatively charged. Regarding the interstitium, it was calculated from the respective time constants, K, that the interstitium/lymph concentration ratio of negative native albumin was 0.96 ± 0.06 of that of neutralized albumin. This suggests the presence of negative fixed charges repelling negative native albumin. However, since the calculated charge density of — 1.8 ± 1.2 mEq 1^--¹ was not significantly different from zero, it is concluded that the renal interstitium is uncharged. This does not, however, rule out the possibility that, for example, negative groups are fixed to the interstitial matrix, merely that the average fixed charge density of renal interstitial fluid is negligible.     

Enhancing High-Temperature Energy Density through Al2O3 Nanoplates with Charge Barrier Effect in Polyetherimide-Based Composites

Polymer-based dielectric composites have a wide range of applications in modern electronics and power systems owing to their incomparable reliability, but remain a challenge to energy density at high temperatures. In this work, polyetherimide (PEI)-based nanocomposites with a small amount of aluminium oxide (Al₂O₃) nanoplates are prepared and obtain excellent energy density at elevated temperatures. The high-temperature energy density of the nanocomposites is significantly improved and reaches to 5.2 J cm⁻³ at 550 kV mm⁻¹ and 150 °C after adding 0.6 wt% Al₂O₃ nanoplates. The enhanced energy density is attributed to the wide band gap and flaky morphology of Al₂O₃ nanoplates that can induce charge barrier effect and thus reduce the leakage current density within the nanocomposites. Furthermore, finite element simulations further reveal the mechanism of Al₂O₃ nanoplates acting as charge barrier to capture the charges transmitted from PEI matrix at the interface. This work offers a promising pathway to high-energy density polymer dielectrics capable of operating under high temperatures.     

Expansion coefficients of hydrolysed polyacrylamides from intrinisc viscosities

Partially hydrolysed polyacrylamide samples were used as model polyelectrolytes and the variations of the intrinsic viscosities with the extent of hydrolysis and molecular weight were used to determine the relative applicability of the various macroion expansion theories. Expanison coefficients solely attributable to the presence of electrostatic charges were calculated with reference to the intrinisic viscosities of the parent polyacrylamides, assuming that the polyacrylamide corresponds to the discharged state of the macroion from hydrolysed polyacrylamides. Similarly, total expansions and expansions attributable to long-range interactions were evaluated using the estimated intrinsic viscosities at the theta temperature of the parent polyacrylamide and the hydrolysed sample, respectively. The electrostatic expansion coefficients are independent of molecular weight and the long-range expansion coefficients are almost independent of the extent of hydrolysis at high charge densities. In the absence of closed expressions predicting the variation of the expansion coefficients with the concentration of ionizable groups, equivalent expressions based on different theories were deduced assuming that i²/C_s is proportional to the concentration of ionizable groups where i is the extent of ionization of the polyelectrolyte and C_s is the concentration of the added salt. The variation of the electrostatic expansion coefficient with the charge density could not be represented according to any of the theories on macroion expansion. However, attributing the total expansion to the presence of electrostatic charges alone, the Fixman and Chien-Ishihara theories allow a good representation of the data. At very low charge densities, the expansions due to long-range interference effects also can be accounted for by the Fixman and Chien-Ishihara theories.     

Die orientierung der kristallinen und der nichtkristallinen bereiche in verstreckten polyethylenterephthalat-folien

Films of poly(ethylene terephthalate) were stretched at 100°C with different stretching rates. By this, oriented films with birefringences between 3.10^?3 and 100.10^?3 were produced. After a crystallization with fixed ends at 150°C, 200°C and 240°C, the orientation function of the crystalline regions, the density, and the birefringence were measured. From this data, the orientation function of the noncrystalline regions was computed. The results obtained show, that only a qualitative but not a quantitative computation of the orientation function is possible. With increasing birefringence of the material before crystallization, the orientation of the crystalline and the noncrystalline regions increases. Up to birefringences of Δn₀=40.10^?3 in both regions a strong increase of the orientation function is observed. At higher birefringences Δn₀, the increase diminishes and depends strongly on the crystallization temperature. The orientation of the crystals after crystallization is better than the initial average orientation of the sample before crystallization. Further the orientation function of former reported structure models for the crystalline regions were computed in dependence of the structure parameters. Comparing the computed and experimental results one finds, that the change from structures consisting of twisted lamellae into such of bended lamellae occurs at a birefringence Δn₀=20.10^?3.     

Tailoring Polyethylene Characteristics Using a Combination of Nickel α‐Diimine and Zirconocene Catalysts under Reactor Blending Conditions

Ethylene was polymerized using a combination of Ni(α‐diimine)Cl₂ ( 1 ) (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) and rac‐ethylenebis(IndH₄)ZrCl₂ ( 2 ) (IndH₄ = 4,5,6,7‐tetrahydro‐1‐η⁵‐indenyl) compounds, activated with methylaluminoxane in toluene. The polymerizations were performed at three different temperatures (0, 30, and 50°C), and the effect of varying the zirconium loading molar fraction (x_Zr) was monitored. The polymerization runs carried out at 0 and 50°C show that the productivity increases linearly with x_Zr. On the other hand, at 30°C the productivity reaches a maximum of 8.19×10³ kg of PE/mol[M]·h for x_Zr = 0.67, indicating a non‐linear correlation between the productivity and x_Zr. The polyethylene characteristics have been evaluated by means of differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and scanning electron microscopy (SEM). The PE produced at 0 and 30°C showed monomodal molecular weight distributions with narrow polydispersities. At higher temperature (50°C), using x_Zr = 0.10, two different polyethylenes were produced; an amorphous rubbery PE with M̄_w of 83×10³ g·mol^–1 and a linear high density PE with M̄_w of 284×10³ g·mol^–1. DSC thermograms of the PE obtained at 0°C (x_Zr = 0.25–0.50) showed the presence of two melting points corresponding to branched and linear PE, indicating a low compatibility between the phases. By SEM it was observed that the branched polyethylene obtained at 0°C forms very small aggregates dispersed in the linear polyethylene matrix, but the polymer obtained at 30°C forms larger particles which show low compatibility with the linear polyethylene.     

Control of shivering and heart rate in incubating bantam hens upon sudden exposure to cold eggs

To distinguish shivering released by cooling of the brood patch from shivering released by low core temperature, incubating bantam hens were exposed to water perfused eggs. Responses to a period of egg cooling were compared to the recovery period after egg temperature had been returned to 40 ^oC, but cloacal temperature (T_b) still was low. At an ambient temperature (T_a) of 23 ^oC and exposure of the hens to between two and eight eggs cooled to 10–35 ^oC (series 1), electromyographic (EMG) activity of musculus iliotibialis increased rapidly with an occasional overshoot, and was higher during egg cooling than during recovery. This hysteresis in EMG activity and T_b was weakly correlated to egg temperature and clutch size. Heart rate (HR) showed an almost parallel increased to shivering except that a maximum HR was reached at high shivering intensities. These responses were also present at a T_a of 37 ^oC when the hens were slightly hyperthermic before exposure to eight eggs at 20 ^oC (Series 2). At the highest starting T_bs EMG activity increased linearly after a drop in T_b. Shivering in m. pectoralis showed a lower threshold T_b and lower activity than m. iliotibialis during egg cooling, and immediately ceased at the end of egg cooling. Total body thermosensitivity estimated from the recovery periods at low and high T_a was –9.7 and –6.4 W kg^-1oC^-1, respectively. It is concluded that shivering in incubating birds warming cold eggs probably is stimulated both by peripheral and central thermoreceptors. The peripheral component shows phasic properties typical for skin receptors.     

Effect of intracellular and extracellular ion changes on E–C coupling and skeletal muscle fatigue

The causative factors in muscle fatigue are multiple, and vary depending on the intensity and duration of the exercise, the fibre type composition of the muscle, and the individual's degree of fitness. Regardless of the aetiology, fatigue is characterized by the inability to maintain the required power output, and the decline in power can be attributed to a reduced force and velocity. Following high-intensity exercise, peak force has been shown to recover biphasically with an initial rapid (2 min) recovery followed by a slower (50 min) return to the pre-fatigued condition. The resting membrane potential depolarizes by 10–15 mV, while the action potential overshoot declines by a similar magnitude. Following high-frequency stimulation of the frog semitendinous muscle, we observed intracellular potassium [K⁺]_i decrease from 142±5 to 97±8 mm , while sodium [Na⁺]_i rose from 16±1 to 49±6 mm . The [K⁺]_i loss was similar to that observed in fatigued mouse and human skeletal muscle, which suggests that there may be a limit to which [K⁺]_i can decrease before the associated depolarization begins to limit the action potential frequency. Fibre depolarization to -60 mV (a value observed in some cells) caused a significant reduction in the t-tubular charge movement, and the extent of the decline was inversely related to the concentration of extracellular Ca²⁺. A decrease in intracellular pH (pH_i) to 6.0 was observed, and it has been suggested by some that low pH may disrupt E–C coupling by directly inhibiting the SR Ca²⁺ release channel. However, Lamb et al. (1992) observed that low pH had no effect on Ca²⁺ release, and we found low pH_i to have no effect on t-tubular charge movement (Q) or the Q vs. V_m relationship. The Ca²⁺ released from the SR plays three important roles in the regulation of E–C coupling. As Ca²⁺ rises, it binds to the inner surface of the t-tubular charge sensor to increase charge (Q_γ) and thus Ca²⁺ release, it opens SR Ca²⁺ channels that are not voltage-regulated, and as [Ca²⁺]_i increases further it feeds back to close the same channels. The late stages of fatigue have been shown to be in part caused by a reduced SR Ca²⁺ release. The exact cause of the reduced release is unknown, but the mechanism appears to involve a direct inhibition of the SR Ca²⁺ channel.     

Nuclear magnetic resonance studies on polymer carbanions, 2. Model compounds for α-methylstyrene and α-methylstyrene tetramer dianions

¹H and ¹³C NMR spectra of model compounds for the poly-α-methylstyryl anion, 2-lithio, 2-potassio, and 2-cesio-2-phenylbutane, were determined. The lithium compound had a higher charge density at the α-carbon and a lower charge on the phenyl ring than the other compounds and exhibited phenyl ring rotation at higher temperatures. The activation energy was calculated to be 61, 0 kJ/mol. The potassium and cesium compounds did not show phenyl ring rotation at 80°C. Quantum chemical calculations indicated that the larger cations interact with the phenyl ring especially with the ortho carbons. ¹³C NMR spectra of α-methylstyrene tetramer dianion with sodium and potassium as counter cation were also measured and compared with those of the model compounds.     

Free radical terpolymerization of three non‐homopolymerizable monomers, 2. Terpolymerization of N‐ethylmaleimide,anethol and trans‐stilbene

The free radical terpolymerization of N‐ethylmaleimide (NEMI), anethol (ANE) and trans‐stilbene (Stb) in CCl₄ at 60°C is described. For the first time, a new kinetic treatment has been applied to this ternary system in order to evaluate the degree of participation of free monomers and charge‐transfer complexes in the polymerization process. It can be shown that at low monomer concentrations, free monomers dominate the polymerization process, at medium monomer concentrations, both species participate to the same extent and at high monomer concentrations, the participation of charge‐transfer complexes increases strongly. The ternary system was also investigated according to the known terminal and complex model. The reactivity ratio according to the terminal model is k₁₂ /k₁₃ = 1,33, the reactivitity ratios according to the complex model are r_I = 1,0 and r_II = 0,7. The equilibrium constants for the formation of CT complexes between NEMI/ANE (C_I) and NEMI/Stb (C_II) at 25°C in CCl₄ were determined to be K_I = 0,34 L·mol^–1 and K_II = 0,21 L·mol^–1, respectively.     

Application of the composite model for the mechanical properties of high density polyethylene

The existing models of high density polyethylene (HDPE) fail to tackle effectively the development of mechanical anisotropy on drawing at different temperatures. This paper is concerned with the theoretical interpretation of the anisotropic elastic properties of HDPE by applying the composite model proposed by the authors. The model takes into account the change in orientation and crystallinity on drawing. As far as the orientational changes on drawing are concerned, it is seen that the pseudo affine deformation law tan θ = ?(n) · tan θ′ with ?(n) = n^?3/2 is applicable at ?60°C only. It is further found that the two parameter analytical form of ?(n) reproduces the correct orientational changes on drawing for the entire temperature range from ?60 to 100°C. The agreement of the calculated values of E₀ and E₉₀ over the entire temperature range at all drawing ratios is quite satisfactory.     

Einfluß des temperns auf die negative thermische ausdehnung von polyethylen

The linear thermal coefficient of expansion for high density polyethylene, extended to draw ratios λ = 8 to 16 is α = ?24·10^?6 K^?1 at 20°C. This value results from the orientation of crystallites with an expansion coefficient α_c = ?12·10^?6 K^?1 and from stresses in the amorphous phase. Using the model of series coupling of crystalline and amorphous parts the value α_am ≤ ?50·10^?6 K^?1 is calculated for a crystallinity x_v = 70%. From measurements of Young's modulus the fraction of tie-molecules χ_tie = 0,4% of the sample is assessed and the expansion coefficient α_tie = ?90·10^?6 K^?1. Annealing of the samples leads to shrinkage while the density ρ increases slightly and the expansion coefficient α increases considerably. Samples annealed at temperatures closely below the melting point show a slight decrease of the density at 20°C but a value of α exceeding that of isotropic samples. This effect can be explained by preferred orientation of the crystal a-axis in fibre direction as soon as orientation starts to break down.     

Developmental changes in Ca2+ currents from newborn rat cardiomyocytes in primary culture

Electrophysiological characteristics of neonatal rat ventricular cardiomyocytes in primary culture were studied using the whole-cell patch-clamp recording technique. Cell size, estimated by measurement of membrane capacitance, was significantly increased throughout the culture from 22.4±5.4 pF at day 2 to 55.0±16.1 pF at day 7, reflecting the hypertrophic process which characterises postnatal cell development. The Ca²⁺ current was investigated at day 2 and 7 of the culture which constituted the early postnatal and maximally developed stages, respectively, of isolated cells in our experimental conditions. At 2 days of culture, two types of Ca²⁺ current could be distinguished, as also observed in freshly dissociated newborn ventricular cells. From their potential dependence and pharmacological characteristics, they could be attributed to the T- (I _Ca-T) and L-type (I _Ca-L) Ca²⁺ current components. After 7 days of culture, only the latterI _Ca-L was present and its density was significantly increased when compared to the density in 2-day-old cells, but lower than that obtained in freshly dissociated adult cells. As the age of the culture progressed, the steady-state inactivation curve was shifted toward negative potentials, in the direction of the inactivation curve obtained for adult cells. Compared to the serum-free control conditions, the density ofI _Ca-L was significantly increased in the presence of fetal calf serum throughout the culture. Consequently, the density ofI _Ca-L obtained in 7-day-old cells was similar to the density ofI _Ca-L obtained in freshly dissociated adult cardiac cells. These results show that in rat neonatal ventricular cardiomyocytes, the changes in Ca²⁺ current during development in primary culture can be compared to that observed in vivo during the first weeks of the postnatal period. The data suggest that the composition of the culture medium is a conditioning factor in the development of cardiac cells in culture. However, the determination and the role of specific factors contained in the serum need to be investigated. The data are also discussed in terms of a possible correlation between the expression and maturation of the Ca²⁺ current components and the capabilities of the neonatal cardiac cells to proliferate and/or to hypertrophy. For these reasons primary cultures of neonatal rat cardiac cells could constitute a valuable in vitro model for studies of postnatal development.     

Unit cell dimensions of poly(ethylene terephthalate)

The density of crystals of poly(ethylene terephthalate), (PETP), Q_c is checked by X-ray diffraction assuming a triclinic unit cell and the indices of reflections as found by Bunn. The following unit cell dimensions are found: a = 4,48Å, b = 5,85Å, c = 10,75 Å, α = 99,5°, β = 118,4°, and γ = 111,2°. This gives the density Q_c as 1,515g/cm³ which is about 4% higher than that reported by Bunn. Negligible differences in spacings for samples annealed at different temperatures (120°C–260°C) have been found. Only for an annealing temperature of 100°C the higher d-values lead to Q_c = 1,484g/cm³. For undrawn PETP films annealed at 250°C the same value of Q_c as for drawn PETP was obtained on the basis of Guinier X-ray patterns. No systematic variation of crystal plane spacings was found for drawn PETP fibers annealed at 220°C and containing mole fractions of 1,7 to 4,2% diethylene glycol, (2,2′-oxydiethanol), as comonomer.     

Structural variations of DNA + Mn2+ complexes during helix-coil transition

The helix-coil transition in Phage T2 DNA in the presence of 6,4 · 10^?3 mol/l Mn²⁺ is studied using light scattering and UV spectroscopy. The transition range is about 0,5°C. Near the temperature of the end of melting T_f the molecular weight M_w and the radius of gyration R_z of the complex are observed to decrease to about one half. At a temperature 0,1–0,25°C higher than T_f, M_w and R_z pass through a minimum, which implies that aggregation is preceded by unwinding of DNA strands. Thus, rise in temperature rather than Mn²⁺ -induced aggregation causes DNA + Mn²⁺ melting.     

Synthesis of two potential NK1-receptor ligands using [1-11C]ethyl iodide and [1-11C]propyl iodide and initial PET-imaging

Background  

The previously validated NK₁-receptor ligand [O-methyl-¹¹C]GR205171 binds with a high affinity to the NK₁-receptor and displays a slow dissociation from the receptor. Hence, it cannot be used in vivo for detecting concentration changes in substance P, the endogenous ligand for the NK₁-receptor. A radioligand used for monitoring these changes has to enable displacement by the endogenous ligand and thus bind reversibly to the receptor. Small changes in the structure of a receptor ligand can lead to changes in binding characteristics and also in the ability to penetrate the blood-brain barrier. The aim of this study was to use carbon-11 labelled ethyl and propyl iodide with high specific radioactivity in the synthesis of two new and potentially reversible NK₁-receptor ligands with chemical structures based on [O-methyl-¹¹C]GR205171.     

U.V./visible spectroscopic study of the rac-Et(Ind)2ZrCl2/MAO olefin polymerization catalytic system, 1. Investigation in toluene

The U.V./visible spectrum of the rac-Et(Ind)₂ZrCl₂/methylaluminoxane (MAO) catalytic system in toluene at 20°C, which is related to the ‘ligand to metal charge transfer’ bands (LMCT), varies greatly with the MAO/Zr ratio (mole ratio Al/Zr). Indeed, for MAO/Zr ratios <30, a hypsochromic shift of the absorption band is observed and is explained by monomethylation of the metallocene dichloride. Conversely, a progressive bathochromic shift of the absorption band is observed for MAO/Zr ratios ranging from 30 to 2000. This behavior is interpreted by the formation of an increasing proportion of dissociated to associated zirconocenium species [L₂ZrX]⁺ [MAOCl]⁻. The λ_max changes of the U.V./visible spectrum of the rac-Et(Ind)₂ZrCl₂/MAO system were correlated with its catalytic activity for the hex-1-ene polymerization. Moreover, a conductimetric study performed on the rac-Et(Ind)₂ZrCl₂/MAO system for different MAO/Zr ratios is also in agreement with the formation of ionic species with different nature and ionization degrees.     

Decay studies of poly(vinyl chloride) electrets

Thermoelectrets of poly(vinyl chloride) were prepared at 4, 14, 20 kV/cm and 105, 115, 125 and 135°C. The final charge is always homocharge, though the initial one depends upon the polarizing parameters. With 4 and 14 kV/cm, up to 125°C, the initial charge is homo, increasing with the polarizing temperature T_p. At 135°C, it is heterocharge tending to increase with the polarizing field E_p. From the thermally stimulated depolarization glow curves, the number of dipoles per monomeric unit of the material is calculated; it is seen that this number cannot account for the heterocharge. A mica spacer placed between the dielectric and one electrode suppresses the peak current. A model is proposed to explain the electret behaviour.