Omega Cm2 Research Articles

Kinetics of biochemical, electrophysiological and morphological events (including lysosomal disorder) during the course of suramin-induced differentiation of the human colon-cancer cell clone HT29-D4

Suramin, a polysulfonated naphtylurea, has been shown to bind to a wide variety of tumor growth factors, and to exhibit anti-proliferative effects on several cell lines. We have followed the suramin-induced (100 micrograms/ml) evolution of morphological, biochemical and electrophysiological changes in HT29-D4 human colonic adenocarcinoma cell clone as a function of culture time. After 5 days of culture in the presence of the drug the cells were polarized and exhibited apical brush border and tight junctions. The polarization process of carcino-embryonic antigen (CEA) in the apical membrane domain was achieved after 8 days of treatment, while the correct localization of HLA class-I molecules in the basolateral membrane domain occurred after 14 days of culture in the presence of suramin. Spontaneous potential difference (PD) and transepithelial resistance (Rt) were recorded from the 9th day of treatment and reached maximum values at day 15 (PD = 3 mV; RT = 450 omega cm2), giving evidence that the differentiation process triggered by suramin concerned virtually all cells in the monolayer. Untreated cells were consistently found to be electrically inactive. Finally, from day 10 of suramin treatment, the lysosomal system was perturbed including accumulation of large autophagic vacuoles and, later, typical lamellar inclusion bodies. These structures were never seen when cells were induced to differentiate in suramin-containing serum-free medium. Moreover, similar perturbations of the lysosomal system could be obtained by adding BSA in the suramin-containing defined medium, suggesting that the lysosomal storage disorder occurring upon suramin treatment was due to endocytosis of suramin-BSA complexes. We conclude that lysosomal impairment due to the presence of BSA in the culture medium did not prevent HT29-D4 cells from differentiating and that it was not an early event which could be involved in the mechanism of action of suramin. However, this perturbation might account for some of the toxic effects occurring during chronic suramin treatment in humans.

Regulation of Transepithelial Electrical Resistance in Two-Compartment Sertoli Cell Cultures:In VitroModel of the Blood-Testis Barrier*

The effects of FSH, testosterone (T), and incubation temperature on the development of inter-Sertoli cell (Sc) tight junctions were investigated in vitro by using repetitive measurements of transepithelial electrical resistance (TER). Control cultures developed stable TER of 100-145 omega cm2 during the initial 3-4 days of incubation at either 33 or 36.5 C, suggesting the formation of simple but continuous tight junctions. The presence of FSH (200 ng/ml) at 33 C delayed the onset of TER development by 3-5 days. The addition of FSH at the time of stable TER (day 5) resulted in a rapid (24 h) decrease of TER to 35-40 omega cm2, which returned to the control level during the subsequent 5-7 days. T alone (0.001-10 microM) caused an early and dose-dependent increase in TER to 165-240 omega cm2. In mono-layers incubated at 36.5 C, the continuous presence of FSH resulted in a dose-dependent increase in TER, which stabilized at 260-380 omega cm2 after 4-6 days. At this temperature, the addition of FSH on day 5 caused a rapid drop of TER similar to that observed at 33 C. This drop could not be prevented by antiproteases (aprotinin, epsilon-aminocaproic acid, or 10% fetal bovine serum) and was followed by an increase in TER up to 260-300-omega cm2. The Sc monolayers developed FSH-induced TER of 230-280 omega cm2 at 33 C, but only after several days of culture at 36.5 C. The effects of T at 36.5 and 33 C were similar, but the maximal TER values were significantly higher (290-380 omega cm2) at 36.5 C. The concomitant presence of T and FSH at 36.5 C resulted in the highest TER levels (580-1200 omega cm2) within 4-6 days, suggesting the synergistic effect of the two hormones on TER development. Dihydrotestosterone was more effective than T when used together with FSH, whereas estradiol had no effect. The different patterns of TER did not result from differences in Sc number or metabolic activity and probably reflected developmental and/or maturational changes in the inter-Sc tight junctions. It is concluded that FSH, T, and temperature play a role in the development of high TER by Sc monolayers (formation of tight junctions) in vitro. FSH and T appear to regulate TER via separate pathways and to cooperate by a yet unknown synergistic mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of NaCl reabsorption by antidiuretic hormone in the cortical thick ascending limb of Henle's loop of the mouse

The effect of antidiuretic hormone (ADH) on transepithelial Na+ Cl-, Ca2+ and Mg2+ net fluxes (JNa, JCl, JMg, JCa) was investigated in isolated perfused cortical thick ascending limb segments (cTAL) of the mouse nephron, using the microperfusion technique and the electron microprobe analysis to determine the ionic composition of the collected tubular fluid. Simultaneously, the transepithelial potential difference (PDte) and the transepithelial resistance (Rte) were recorded. Prior to the flux measurements cTAL segments were perfused for one hour. During this equilibration period PDte decreased significantly from +19.9 +/- 1.6 to +14.9 +/- 1.1 mV and Rte increased from 30.6 +/- 3.5 omega cm2 to 38.8 +/- 2.4 omega cm2 (n = 7), reflecting a decline in NaCl transport. After ADH was added to the bath solution at 10(-10) mol.l-1, PDte increased from +14.4 +/- 1.1 to +18.0 +/- 1.5 mV, accompanied by a rise in JNa and JCl from 205 +/- 11 to 273 +/- 19 and from 216 +/- 12 to 283 +/- 21 pmol.min-1.mm-1 (n = 7), respectively. JCa and JMg also increased from 0.81 +/- 0.07 to 1.50 +/- 0.12 and from 0.43 +/- 0.11 to 0.76 +/- 0.08 pmol.min-1.mm-1 (n = 7), respectively. All these effects were fully reversible after withdrawal of the hormone. In conclusion our data indicate that ADH stimulates divalent cation transport and NaCl transport in the cortical thick ascending limb of Henle's loop of the mouse.

Effect of bicarbonate on potassium conductance of isolated perfused rat pancreatic ducts

The aim of this study was to investigate the role of the K+ conductance in unstimulated and stimulated pancreatic ducts and to see how it is affected by provision of exogenous HCO3-/CO2. For this purpose we have applied electrophysiological techniques to perfused pancreatic ducts, which were dissected from rat pancreas. The basolateral membrane potential PDbl of unstimulated duct cells was between -60 mV and -70 mV, and the cells had a relatively large K+ conductance in the basolateral membrane as demonstrated by (a) 20-22 mV depolarization of PDbl in response to increase in bath K+ concentration from 5 mmol/l to 20 mmol/l and (b) the effect of a K+ channel blocker, Ba2+ (5 mmol/l), which depolarized PDbl by 30-40 mV. These effects on unstimulated ducts were relatively independent of bath HCO3-/CO2. The luminal membrane seemed to have no significant K+ conductance. Upon stimulation with secretin or dibutyryl cyclic AMP, PDbl depolarized to about -35 mV in the presence of HCO3-/CO2. Notably, the K+ conductance in the stimulated ducts was now only apparent in the presence of exogenous HCO3-/CO2 in the bath solutions. Upon addition of Ba2+, PDbl depolarized by 13 +/- 1 mV (n = 7), the fractional resistance of the basolateral membrane, FRbl increased from 0.66 to 0.78 (n = 6), the specific transepithelial resistance, Rte, increased from 52 +/- 13 omega cm2 to 59 +/- 15 omega cm2 (n = 11), and the whole-cell input resistance, Rc, measured with double-barrelled electrodes, increased from 20 M omega to 26 M omega (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Technology of fabrication and electrical characteristics of W, Mo, Ni and Ir, Pd contacts with YBa2Cu3O7-x

The technology of fabrication and the properties of metallic electrical contacts on ceramics of YBa2Cu3O7-x superconductors have been studied. Contacts were deposited using the method of metal-organic chemical vapour deposition (MOCVD) for Ir, Pd and the method of exploding wires for W, Mo, Ni. The contacts, prepared by evaporation of Ir in oxygen atmosphere, have specific contact resistance rho c of about 10-5 Omega cm2. Since the temperature of deposition of contacts is 300-400 degrees C (i.e. lower than 500 degrees C, the temperature at which chemical interaction on the YBa2Cu3O7-x-Si, SiC, SiO2 boundary starts), such a technique can be incorporated into silicon-compatible technologies. It has been shown that good adhesion and specific contact resistivities of approximately 10-2 Omega cm2 for W and Ni and approximately 10-3 Omega cm2 for Mo can be achieved. After subsequent annealing rho c reaches 10-6, 7*10-5, 7*10-3 and 10-2 Omega cm2 for Ir, Ni, W and Mo, respectively.

Correlation of zonula occludens ZO-1 antigen expression and transendothelial resistance in porcine and rat cultured cerebral endothelial cells

Cerebral endothelial cell cultures (CECC) have been utilized as an in vitro system for simulating the blood-brain barrier. We have studied the expression of a tight junction associated protein (ZO-1) concomitantly with measurements of transendothelial electrical resistance and freeze-fracturing to test the barrier properties of CECC monolayers and, thereby, their capability in serving as an in vitro blood-brain barrier model. Freshly isolated CECC aggregates and 7 day old CECCs in primary culture express the ZO-1 protein. Measurements of the transcellular resistance of CECC monolayers yielded an electrical resistance of about 90 omega cm2. The low electrical resistance of cerebral endothelial monolayers together with the reduced complexity of the tight junction complement in vitro are indicative of reduced barrier properties of the in vitro system.

Conductance rise induced by the calcium ionophore A23187 in unfertilized eggs of tilapia

Current-clamp measurements on unfertilized tilapia eggs gave linear current-voltage relations in the range 0 to -120 mV. Eggs had low resting potentials (-22 mV) and high specific membrane resistances (500 k omega cm2) and specific membrane capacitances (0.9 microF cm-2) indicating no marked folding of their plasma membrane. Application of A23187 induced a small depolarization and a conductance rise, the response having a reversal potential of about -16 mV. The results suggest that tilapia eggs have a calcium-gated conductance probably activated at fertilization.

Apical and basal membrane ion transport mechanisms in bovine retinal pigment epithelium.

1. Intracellular voltage recordings using conventional and double-barrelled chloride-selective microelectrodes have been used to identify several transport mechanisms at the apical and basolateral membranes of the isolated bovine retinal pigment epithelium (RPE)-choroid preparation. Intracellular recordings were obtained from two cell populations, melanotic (pigmented) and amelanotic (non-pigmented). The electrical properties of these two populations are practically identical. For melanotic cells the average apical resting membrane potential (VA) is -61 +/- 2 mV (mean +/- S.E.M., n = 49 cells, thirty-three eyes). For these cells the ratio of apical to basolateral membrane resistance (a) was 0.22 +/- 0.02. The mean transepithelial voltage and resistance were 6 +/- 1 mV and 138 +/- 7 omega cm2, respectively. 2. The apical membrane, which faces the distal retina, contains a Ba(2+)-inhibitable K+ conductance and a ouabain-inhibitable, electrogenic Na(+)-K+ pump. In addition it contains a bumetanide-sensitive mechanism, the putative Na(+)-K(+)-Cl- cotransporter. The basolateral membrane contains a DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid)-inhibitable chloride channel. The relative conductances of the apical and basolateral membranes to K+ and Cl- are TK approximately 0.9 and TCl approximately 0.7, respectively. 3. The ouabain-induced fast phase of apical membrane depolarization (0-30 s) was used to calculate the equivalent resistances of the apical (RA) and basolateral (RB) cell membranes, as well as the paracellular or shunt resistance (RS). They are: 3190 +/- 400, 17920 +/- 2730 and 2550 +/- 200 omega (mean +/- S.E.M., n = 9 tissues), respectively. From these data the equivalent electromotive forces (EMF) at the apical (EA) and basolateral (EB) membranes were also calculated. They are: -69 +/- 5.0 and -24 +/- 5.0 mV, respectively. 4. Intracellular Cl- activity (aiCl) was measured using double-barreled ion-selective microelectrodes. In the steady state aiCl = 61 +/- 4.0 mM and the Nernst potential ECl = -13.5 +/- 1.5 mV (mean +/- S.E.M., n = 4). 5. In the intact eye or in retina, RPE-choroid preparations it has been shown that the transition between light and dark alters the K+ concentration in the extracellular (or subretinal) space between the photoreceptors and the apical membrane of the RPE. These light-induced changes in subretinal [K+]o were qualitatively simulated in vitro by altering apical K+ between 5 and 2 mM. This produced a sequence of voltage changes at the apical and basolateral membranes that had three operationally distinct phases. Phase 1 is generated by the combination of an apical membrane K+ diffusion potential and inhibition of the electrogenic Na(+)-K+ pump.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical resistance across the blood‐brain barrier in anaesthetized rats: a developmental study.

1. Ion permeability of the blood-brain barrier was studied by in situ measurement of transendothelial electrical resistance in anaesthetized rats aged between 17 days gestation and 33 days after birth, and by electron microscopic examination of lanthanum permeability in fetal and neonatal rats aged up to 10 days old. 2. The blood-brain barrier in 17- to 20-day fetuses had a resistance of 310 omega cm2 but was impermeable to lanthanum, and therefore had properties intermediate between leaky and tight epithelia. 3. From 21 days gestation, the resistance was 1128 omega cm2, indicating a tight blood-brain barrier and low ion permeability. There was little further change in barrier resistance after birth, and in 28- to 33-day rats, when the brain barrier systems are mature in other ways, vessels had a mean resistance of 1462 omega cm2. 4. In the tight blood-brain barrier, arterial vessels had a significantly higher resistance than venous vessels, 1490 and 918 omega cm2 respectively. In vessels less than 50 microns diameter and within the normal 60 min experimental period, there was no significant variation in vessel resistance. 5. Hyperosmotic shock caused a rapid decay in resistance (maximal within 5 min), and after disruption of the blood-brain barrier, vessel resistance was 100-300 omega cm2 in both arterial and venous vessels, and the effect was reversible. After the application of metabolic poisons (NaCN plus iodoacetate) and low temperature there was a similarly low electrical resistance. 6. It is concluded that the increase in electrical resistance at birth indicates a decrease in paracellular ion permeability at the blood-brain barrier and is required for effective brain interstitial fluid ion regulation.

Vectorial Secretion of Inhibin by Immature Rat Sertoli Cells in Vitro: Reexamination of Previous Results*

The vectorial secretion of immunoactive and bioactive inhibin by immature rat Sertoli cells (Sc) cultured in a two-compartment system was investigated using various culture supports. When Sc were cultured on Millipore-HA filters (used in all previous studies on vectorial secretion of inhibin), both immuno- and bioactive inhibin were found almost exclusively in the apical compartment, suggesting predominantly apical secretion of the glycoprotein. However, the cell-free Millipore-HA filters completely blocked the passage of Sc-conditioned medium (SCCM) inhibin, even after pretreatment with BSA and SCCM to saturate the protein-binding sites. On the other hand, polycarbonate Nucleopore filters or Millicell-CM membranes, both exhibiting extremely low protein-binding capacity, did not significantly block the passage of SCCM inhibin. When Sc were cultured on Nucleopore filters, the immunoactive inhibin was detected in both culture compartments; the basal compartment/apical compartment (BC/AC) ratio was about 1.5 (range, 1.2-1.9). The maximal effective dose of FSH or (Bu)2cAMP caused a 6- to 9-fold increase in the total (BC plus AC) secretion of immunoactive inhibin, but only a 60% increase in the secretion of bioactive inhibin, as evaluated by RIA and pituitary cell bioassay, respectively. The latter phenomenon was not accompanied by any significant change in the basal/apical distribution of either bioactive nor immunoactive inhibin. The presence of testosterone alone (10(-6) M) did not affect either total immunoactive inhibin secretion or its BC/AC ratio. The effects of the concomitant presence of FSH and testosterone did not differ significantly from those of FSH alone. Similarly to testosterone, the lack of any significant effect was observed for 17 beta-estradiol, dihydrotestosterone, androstenediol, and androstenedione regardless of the presence or absence of FSH. The striking dissimilarity of BC/AC ratios of inhibin noted in cultures maintained on Millipore-HA and Nucleopore filters was not due to differences in permeability barrier or Sc functional polarity. When cultured on either support, Sc monolayers developed comparable permeability barriers, as evaluated by measuring the passage of [3H]inulin and development of electrical resistance. The maximal electrical resistance (130-150 omega cm2) developed after 6-8 days of culture on either support. Also, total transferrin secretion and transferrin BC/AC ratio were similar on both supports, suggesting comparable cell numbers and functional polarities. These findings demonstrate that immature Sc in vitro secrete inhibin bidirectionally (BC/AC ratio, approximately 1.5); the polarity of secretion is unaffected by either FSH or various naturally occurring steroids, including testosterone.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of cell membrane resistance in cultured renal epithelioid (MDCK) cells: effects of cadmium and mercury ions

Previous studies have indicated that the cell membrane of Madin Darby Canine Kidney (MDCK) cells is hyperpolarized by a number of hormones and trace elements, in parallel with an enhancement of potassium selectivity. Without knowledge of the cell membrane resistance (Rm), however, any translation of potassium selectivity into potassium conductance remains equivocal. The present study was performed to determine the Rm of MDCK cells by cellular cable analysis. To this end, three microelectrodes were impaled into three different cells of a cell cluster; current was injected via one microelectrode and the corresponding voltage deflections measured by the other two microelectrodes. In order to extract the required specific resistances, the experimental data were analysed mathematically in terms of an electrodynamical model derived from Maxwell's equations. As a result, a mean Rm of 2.0 +/- 0.2 k omega cm2 and an intercellular coupling resistance (Rc) of 6.1 +/- 0.8 M omega were obtained at a mean potential difference across the cell membrane of -47.0 +/- 0.6 mV. An increase of the extracellular K+ concentration from 5.4 to 20 mmol/l depolarized the cell membrane by 16.2 +/- 0.5 mV and decreased Rm by 30.6 +/- 3.0%; 1 mmol/l barium depolarized the cell membrane by 20.1 +/- 1.1 mV and increased Rm by 75.9 +/- 14.3%. Omission of extracellular bicarbonate and carbon dioxide at constant extracellular pH caused a transient hyperpolarization (up to -60.4 +/- 1.4 mV), a decrease of Rm (by 75 +/- 4.5%) and a decrease of Rc (by 23.1 +/- 8.4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin‐enhanced urea transport by rat inner medullary collecting duct cells in culture

The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)-regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen-coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 +/- 22 omega cm2. In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 +/- 0.4 to peak values of 16.0 +/- 3.8 (10 nM), 23.1 +/- 3.9 (1 microM) and 28.1 +/- 4.9 (10 microM) x 10(-6) cm s-1 (n = 24). In 10 other monolayers, after the addition of 1 mM 8-Br-cAMP, urea permeability increased from 5.1 +/- 0.3 to 8.1 +/- 1.6 x 10(-6) cm s-1 and, after 8-Br-cAMP + 3-isobutyl-1-methylxanthine, to 12.2 +/- 0.7 x 10(-6) cm s-1. We conclude that rat IMCD cells grown in culture exhibit the characteristics of a 'tight' epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes. Furthermore, IMCD cells retain the capacity for AVP-regulated urea permeability, a characteristic feature of this nephron segment in vivo.

Amiloride-sensitive Na+ transport across cultured renal (A6) epithelium: evidence for large currents and high NaK selectivity

Electrical techniques were used to determine the Na:K selectivity of the amiloride-sensitive pathway and to characterize cellular and paracellular properties of A6 epithelium. Under control conditions, the mean transepithelial voltage (VT) was -57 +/- 5 mV, the short-circuit current (Isc) averaged 23 +/- 2 microA/cm2 and the transepithelial resistance (RT) was 2.8 +/- 0.3 k omega cm2 (n = 13). VT and Isc were larger than reported in previous studies and were increased by aldosterone. The conductance of the amiloride-sensitive pathway (Gamil) was assessed before and after replacement of Na+ in the mucosal bath by K+, using two independent measurements: (1) the slope conductance (GT), determined from current-voltage (I-V) relationships for control and amiloride-treated tissues and (2) the maximum amiloride-sensitive conductance (Gmax) calculated from the amiloride dose-response relationship. The ratio of Gamil in mucosal Na+ solutions to Gamil for mucosal K+ solutions was 22 +/- 6 for GT measurements and 15 +/- 2 for Gmax data. Serosal ion replacements in tissues treated with mucosal nystatin indicated a potassium conductance in the basolateral membrane. Equivalent circuit analyses of nystatin and amiloride data were used to resolve the cellular (Ec) and paracellular (Rj) resistances (approximately 5 k omega cm2 and 8-9 k omega cm2, respectively). Analysis of I-V relationships for tissues depolarized with serosal K+ solutions revealed that the amiloride-sensitive pathway could be described as a Na+ conductance with a permeability coefficient (PNa) = 1.5 +/- 0.2 x 10(-6) cm/s and the intracellular Na+ concentration (Nai) = 5 +/- 1 mM (n = 5), similar to values from other tight epithelia. We conclude that A6 epithelia are capable of expressing large amiloride-sensitive currents which are highly Na+ selective.

Madin-Darby canine kidney cells

Vectorial transport of salt and water in the Madin-Darby canine kidney (MDCK) cell line is indicated by the formation of domes when a monolayer is grown on an impermeable support. We investigated aldosterone-induced dome formation and evaluated the dome as an experimental model. Transepithelial dome resistance was about 80 omega cm2 and constant when dome size exceeded 2.10(-4) cm2. The relative ion conductances (expressed as transference numbers) across the dome epithelium were tNa:tCl:tk = 0.64:0.24:0.06. They reflect the permeability properties of the paracellular shunt pathway tested at physiological concentrations of the individual ions. Aldosterone accelerated dome formation in serum-deprived MDCK monolayers. Prostaglandin E1 and transferrin were supportive but not essential for aldosterone-induced dome formation. After 72 h dome density was equal in monolayers cultured in serum-supplemented medium either in the presence or absence of mineralocorticoids. We conclude that aldosterone induces cell polarization in MDCK monolayers, leading to the formation of domes. The dome epithelium appears to be electrically isolated from the adjacent monolayer and can be studied by microelectrode techniques.

Germanium-palladium ohmic contacts to n-type GaAs

Ohmic contacts to n-GaAs (Si doped at 2.7*1015 cm-3 and 4.5*1018 cm-3) have been formed using a Ge/Pd/GaAs metallisation and annealing for short times yielding specific contact resistivities ( rho c) of 2.27*10-4 Omega cm2 for low-doped epilayers and 1.25*10-6 Omega cm2 for high-doped epilayers. The resulting contacts display a smooth surface and sidewalls. Contact has also been made to two modulation doped structures with specific contact resistivities of 4.22*10-4 and 1.09*10-4 Omega cm2 using the same metal system.

An Easier, Reproducible, and Mass‐Production Method to Study the Blood–Brain Barrier In Vitro

To provide an "in vitro" system for studying brain capillary function, we have developed a process of coculture that closely mimics the "in vivo" situation by culturing brain capillary endothelial cells on one side of a filter and astrocytes on the other. Under these conditions, endothelial cells retain all the endothelial cell markers and the characteristics of the blood-brain barrier, including tight junctions and gamma-glutamyl transpeptidase activity. The average electric resistance for the monolayers was 661 omega cm2. The system is impermeable to inulin and sucrose but allows the transport of leucine. Arabinose treatment increases transcellular transport flux by 70%. The relative ease with which such monolayers can be produced in large quantities would facilitate the "in vitro" study of brain capillary functions.

Zinc diffusion from spin-on glass for the formation of low-resistance Schottky contacts to p-type GaInAs

A systematic study of zinc incorporation as a function of both time and temperature of heat treatment has shown that the surface zinc concentration in MOVPE p-type GaInAs can be increased from an as-grown maximum of 2*1019 to approximately 1*1020 atoms/cm3 by diffusion from a spin-on glass source. Specific contact resistance values much lower than 1*10-5 Omega cm2 have been achieved after such diffusion. These values were found to depend on the type of p-doping elements used in the as-grown double heterostructures. Light-emitting devices incorporating such low-resistance contacts have predicted lifetimes in excess of 300 years. An advantage on the spin-on glass diffusion process is its suitability for large-scale device production.

Electrophysiological study of inner medullary collecting duct of hamsters

The electrophysiological properties of the hamster mid-inner medullary collecting duct (IMCD2) cells were examined in isolated and perfused preparations by intracellular impalement with conventional 1 mol/l KCl microelectrodes and cable analysis. The transmural voltage (VT) was not different from 0 mV, while the basolateral transmembrane voltage (VB) was -81.7 +/- 0.91 mV (n = 221). The transmural resistance (RT) was 109 omega cm2, indicating that the IMCD2 is composed of tight epithelia. The fractional apical membrane resistance (fRA) was 0.98 +/- 0.003 (n = 10). Abrupt changes in the luminal concentration of Na+, K+ or Cl- did not alter the apical membrane voltage (VA) or VT, and neither 2 mmol/l Ba2+ nor 10 mumol/l amiloride in the lumen affected VA and VT. Moreover, pretreatment of hamsters with deoxycorticosterone acetate (5 mg/kg, s.c.) for 10-14 days caused only a very small change in VT in the negative direction. Amiloride in the lumen increased RT and increased the voltage divider ratio very slightly. However, an abrupt increase in K+ concentration in the bath from 5 mmol/l to 50 mmol/l or addition of 2 mmol/l Ba2+ to the bath depolarized the basolateral membrane by 39 mV and 29 mV, respectively. In the presence of 2 mmol/l Ba2+ in the bath, a reduction of HCO3- concentration from 25 mmol/l to 2.5 mmol/l depolarized VB by 20.4 mV. No Cl- conductance was demonstrated in the basolateral membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of antidiuretic hormone, parathyroid hormone and glucagon on transepithelial voltage and resistance of the cortical and medullary thick ascending limb of Henle's loop of the mouse nephron

The effect of antidiuretic hormone (arginine vasopressin, AVP, 10(-10) mol.l-1), parathyroid hormone (PTH, 10(-8) mol.l-1) and glucagon (10(-8) mol.l-1) on the transepithelial potential difference (PDte) and the transepithelial resistance (Rte) were tested in in vitro perfused cortical (cTAL) and medullary (mTAL) thick ascending limbs of Henle's loop of the mouse nephron. When compared with mTAL segments (PDte: 8.5 +/- 0.4 mV, n = 16), cTAL segments displayed a high PDte of 15.7 +/- 0.9 mV (n = 11) at the beginning of perfusion experiments which reached a value of 9.4 +/- 0.6 mV (n = 11) after 38 +/- 4 min perfusion. Simultaneously Rte increased significantly from 24 +/- 3 to 28 +/- 1 omega cm2 (n = 11). When PTH, AVP or glucagon were added to the bath solution, PDte increased with PTH from 10.3 +/- 0.8 to 15.2 +/- 0.8 mV (n = 13), with AVP from 10.2 +/- 0.5 to 15.0 +/- 0.7 mV (n = 24) and with glucagon from 11.3 +/- 1.9 to 15.3 +/- 2.1 mV (n = 8). At the same time Rte decreased from 30 +/- 3 to 23 +/- 2 omega cm2, from 28 +/- 1 to 23 +/- 1 omega cm2 and from 23 +/- 2 to 18 +/- 2 omega cm2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

P-on-n arsenic-activated junctions in MOCVD LWIR HgCdTe/GaAs

Low-leakage high-performance photovoltaic detectors were fabricated from long-wavelength infrared (LWIR) HgCdTe epitaxial material grown by metal-organic chemical vapour deposition (MOCVD) on GaAs substrates. Layers were grown by two different MOCVD techniques, a conventional alloy growth and an interdiffused multiple-layer growth. MOCVD HgCdTe layers were characterised by background electron concentrations of (1-3)*1015 cm-3 with electron mobilities up to 200000 cm2 V-1 s-1 at 77 K. Surface and cross-section dislocation densities were 106-107 cm-2 and occasionally (4-5)*105 cm-2. GaAs substrates were (100) and (111B) misoriented towards 110. The layer structure in which the devices were fabricated consisted of an absorbing LWIR HgCdTe layer grown on a buffer of CdTe. A thin layer (1-2 mu m) of wide-band-gap HgCdTe was grown last. Devices were fabricated in a single as well as double layers using a mesa geometry with a native oxide passivation. Junctions were formed at 2-3 mu m depth by a low-energy arsenic implant ( approximately 100 keV) which behaved as a finite diffusion source during the post-implant anneal. The best measured zero-bias resistance-area products (R0A) at 77 K were 1.67 Omega cm2 for the alloy layers for a cut-off wavelength of lambda c=14.94 mu m and 7.22 Omega cm2 for the interdiffused multiple layers for lambda c=15.92 mu m at 77 K. The results indicated a definite device performance improvement in double-layer compared to single-layer structures. Analysis of the transport properties for a device fabricated in a single layer with a cut-off wavelength of lambda c=8.35 mu m at 77 K and 9.1 mu m at 40 K suggested that the deviation from thermal processes occurs at temperatures of approximately 40 K.