Low Potential Difference Research Articles

Electrical properties of the intestinal mucosa of the chicken and the effects of luminal glucose

Transmural potential difference (PD), short-circuit current (Isc), and electrical resistance (R) were measured in the isolated mucosa of the duodenum, jejunum, ileum, proximal cecum, and rectum in order to characterize the electrical properties of the chicken small and large intestine. The chicken intestine was classified into three categories, regarding its electrical characteristics: 1) the duodenum, with four to five times higher R than the other segments and the lowest PD; 2) the group formed by the jejunum, the ileum, and the proximal cecum, with high PD and low R; 3) the rectum, with low PD and low R. In all segments, the addition of D-glucose into the luminal side stimulates Isc, and this effect can be reversed by phloridzin, indicating that the glucose-induced Isc increase is due to Na+-D-glucose co-transport. The effect of glucose is maximal in the rectum, with a fivefold Isc increase, suggesting that this segment may have an important role in the absorption of Na+ as well as of nutrients co-transported with Na+.

Electrothermal instabilities in MHD boundary layers

Electrothermal instabilities occurring in the boundary layers of MHD generator channels can cause the breakdown of the electrostatic sheath and lead to the transition from the diffuse to an arc mode current transport. This instability may occur at the electrostatic sheath edge and the arc can punch through the sheath from the plasma side. A stability analysis, carried out for the occurrence of the instability, however, shows that the values of the critical parameter for the onset of instability at the sheath edge were much less than the critical values for breakdown from the electrode plasma interface. Since the perturbations occurring at the sheath edge were found to get damped at higher applied potentials, it is predicted that the instability occurring at the sheath edge at low potential differences cannot lead to the arc transition, but may lead to fluctuations in the values of observable parameters.

Properties of two multisubstate Cl- channels from human syncytiotrophoblast reconstituted on planar lipid bilayers.

We describe the first successful reconstitution of placental ionic channels on planar lipid bilayers. An apical plasma membrane-enriched vesicle fraction from human syncytiotrophoblast at term was prepared by following isotonic agitation, differential centrifugation, and Mg2+-induced selective precipitation of nonapical membranes, and its purity was assessed by biochemical and morphological marker analysis. We have already reported that, unlike previous patch-clamp studies, nonselective cation channels were incorporated in most cases, a result consistent with the higher permeability for cations as compared with Cl- and with the low apical membrane potential difference at term revealed by fluorescent probe partition studies, and microelectrode techniques. In this paper, we report that Cl--selective channels were incorporated in 4% of successful reconstitutions (14 out of 353) and that their analysis revealed two types of activity. One of them was consistent with a voltage-dependent, 100-pS channel while the other was consistent with the lateral association of 47-pS conductive units, giving rise to multibarrelled, DIDS-sensitive channels of variable conductance (300 to 650 pS). The latter displayed a very complex behavior which included cooperative gating of conductive units, long-lived substates, voltage-dependent entry into an apparent inactivated state, and flickering activity. The role of the reported Cl- channels in transplacental ion transport and/or syncytium homeostasis remains to be determined.

Electrolyte Transport Responses to Secretagogues in Neonatal versus Adult Rabbit Jejunum

The ability of the neonatal and adult rabbit jejunum to respond to different exogenous stimuli of electrolyte transport was investigated in vitro. When mounted in Ussing chambers, jejunum from neonatal rabbits exhibited a higher basal short circuit current and lower potential difference compared to jejunum from adult rabbits. As a result, basal conductance was approximately 50% higher in the neonatal group. When the tissue was subjected to electrical field stimulation, neonatal jejunum was significantly less responsive to stimulation with respect to change in short circuit current, particularly at submaximal stimulus strength and stimulus duration. The neonatal jejunum was less responsive than adult jejunum to exogenous application of prostaglandin E2 and 5-hydroxytryptamine, and more responsive to histamine. There was no significant difference in the responses to carbachol, epinephrine, leukotriene D4 or platelet-activating factor. The neonatal rabbit jejunum exhibited a greater capacity to synthesize prostaglandin E2 and the peptidoleukotrienes, and had a higher tissue content of 5-hydroxytryptamine than the adult rabbit jejunum.

Transtrophoblast and microvillus membrane potential difference in mature intermediate human placental villi

Single mature intermediate villi from term placentas after normal gestation and vaginal or cesarian delivery were identified microscopically and mounted in a bath for conventional micro-electrode studies. With the application of strict selection criteria, the following observations on electrical potential difference (PD) were made. 1) With the tissue bathed in Earle's medium (37 degrees C) the PD across the syncytiotrophoblast microvillus membrane with respect to the bath was not normally distributed. The median PD was -22 mV (range -12 to -60 mV, n = 200). This fell to -6 mV after prior incubation for 4 h with cyanide (3 mM) or iodoacetate (2 mM) but was not altered by short-term application of these agents or by 0.1 mM ouabain. Substituting Na+ in Earle's medium with choline had no effect on PD, but replacing Cl- with gluconate caused a depolarization of 6 mV (P < 0.002). Increasing KCl in the bath fluid revealed an apparently low microvillus membrane K+ conductance. The low microvillus membrane PD may reflect a low Na(+)-K(+)-ATPase activity and/or a low membrane permeability to K+. 2) The transtrophoblast PD measured by insertion and withdrawal of the electrode was significantly different from zero [P < 0.003, median -3 mV (range 0 to -15 mV), n = 11]; and PD measured by insertion of the electrode into the villus core and beyond was -6 mV (significantly different from zero P < 0.003, range -2.5 to -10 mV, n = 6). If a similar PD were to exist in vivo, it could have a significant influence on ion transport across the placenta at term.

Negative ion formation in electrospray mass spectrometry

Negative ion electrospray (ES) operating on a single quadrupole mass spectrometer for the detection of low-molecular-weight molecules is discussed. The ES interface was operated at a positive cylindrical electrode potential to produce negative ions, and the results obtained were compared to the positive ion mode. As in the case of operation in the more common positive mode, negative ions with varying degrees of solvation and structurally relevant fragments can be obtained from a variety of solute species, including β-lactam antibiotics, aminoglycosides, aminocyclitols, tetracyclines, sulfonamides, nucleotides, peptides, and explosives. No fragmentation of parent species, except those from some labile explosives, was provided because low potential differences are applied between the capillary and the first skimmer, and electrical discharge is avoided in the gas phase. An increase in the capillary voltage resulted in collision-induced decomposition to produce structurally relevant fragment ions in both operation modes. An evaluation of representative chromatographic solvents indicated that 2-propanol added with oxygen in the ES bath gas is best suited to suppress electrical (corona) discharge phenomena in negative ion operation, whereas it aids in solution nebulization, desolvation, and transfer of ions in solution to the gas phase. For positive ion mode, no such precaution was necessary. Conditions that promote the formation of ions in solution usually improve ES response. Therefore, an increase in the solvent pH can increase the sensitivity in negative ion ES ionization. Negative ion ES offers the advantage of providing complementary structural information to help in the characterization of an unknown compound or to confirm a certain tentatively proposed structure. Nucleotides and explosives were best characterized in negative ion mode owing to the ease with which they form anions in solution, and they could be detected down to the 1-pg/μL level.

Schottky barrier formation at nonreactive interfaces: Ga/GaAs(100) and Pb/GaAs(100)

The chemistry, overlayer morphology, and band bending occurring upon room temperature deposition of Ga and Pb on GaAs(100) are studied via high resolution photoemission spectroscopy, low energy electron diffraction and contact potential difference measurement. Both interfaces are abrupt and unreacted. At submonolayer coverage, Ga and Pb grow two dimensionally on GaAs(100). An ordered (1×2) superstructure is obtained for Pb(1/2 ML)/GaAs(100) by low temperature annealing of the interface (∼300 °C). Clustering is dominant at high coverage. With Ga, the Fermi level (EF) converges toward a position 0.68 eV above the valence band maximum (VBM), in agreement with the position obtained for the GaAs(110) surface. The room temperature deposition of Pb leads to EF stabilization at 0.57 eV above VBM, independent of the initial surface stoichiometry (Ga or As rich). The evolution of the band bending as a function of metal coverage emphasizes in both cases the importance of adatom-induced states at low coverages and the transition to final EF position upon metallization, in support of models based on metal-induced gap states.

Electron transport system associated with direct glucose oxidation in Gluconobacter oxydans

The mode of electron transport associated with the dehydrogenase enzymes located on the cytoplasmic membrane inGluconobacter oxydans (ATCC 9937) has been postulated. High turnover of dehydrogenases under oxygen enrichment conditions is explained on the basis of a simplistic electron transport chain comprising cytochrome c553 (MW 23000) as a subunit of dehydrogenase and a cytochrome b562. The electron transport chain under low dissolved oxygen tension (DOT) is shown to comprise a number of cytochrome c species with very low midpoint potential difference.

Unique characteristics of the neonatal intestinal mucosal barrier

The purpose of this study was to compare the newborn and weanling intestinal mucosa to determine differences in: (1) the electrophysiologic characteristics of the mucosal barrier; (2) the effects of glutamine supplementation on these physiological characteristics; and (3) transmucosal bacterial passage. The Ussing chamber was used to study ileal mucosa from newborn (1 to 4 days old) and weanling (21 days old) piglets. After the seromuscularis was stripped off the bowel wall, the mucosa was mounted in the chamber and perfused with Hanks Balanced Salt Solution (HBSS) or HBSS + 20 mmol/L of glutamine. Following initial stabilization, potential difference (PD) and resistance (R) were measured at 30-minute intervals for 2 hours. Transmucosal bacterial passage was measured by quantitative cultures of the mucosal and serosal reservoirs obtained 2 hours after adding 10 8 E coli C-25 to the mucosal reservoir. Six groups of membranes were studied: (1) newborn and HBSS; (2) weanling and HBSS; (3) newborn and HBSS + glutamine; (4) weanling and HBSS + glutamine; (5) newborn — HBSS + glutamine + E coli; and (6) weanling — HBSS + glutamine + E coli. Newborn ileal mucosa had significantly lower PD and R compared with weanling at all time points. Glutamine led to a significant increase in PD in both newborn and weanling. Newborn mucosa had a significantly increased incidence of transmucosal bacterial passage ( 4 7 ) compared with weanling ( 0 10 ). These findings suggest that: (1) newborn mucosal barrier has uniquely different electrophysiologic characteristics; (2) glutamine improves the metabolic activity as measured by PD in both newborn and weanling; and (3) the newborn mucosal barrier allows increased transmucosal passage of bacteria.

Seasonal patterns of cell‐to‐cell communication in Chara corallina Klein ex Willd. I. Cell‐to‐cell communication in vegetative lateral branches during winter and spring

ABSTRACTCell‐to‐cell communication in lateral branches of limited growth in male Chara corallina plants has been studied using fluorescent plasmalemma‐impermeable probes. The extent of cell‐to‐cell communication was found to be seasonal. In winter, branch internodes were characterized by relatively low plasmalemma potential differences (–121·2±23·2 mV; [K+]o 0·5 mol m−3; pH 7·6), quiescent dactyls isolated from the symplast (conic tips) and by restricted cell‐cell communication (frequency of intercellular transport of six carboxyfluorescein = 42·9%). Cell‐to‐cell communication was inhibited during action‐potentials, and was more extensive between cells which did not give an action potential in response to a current pulse. An inhibitor of the action potential, La3+, promoted cell‐to‐cell communication. These may be characteristic features of winter dormancy in lateral branches of Chara. In spring, morphological and electrophysiological changes occurred immediately prior to the onset of fertility. Characteristic changes in morphology included increased abundance of spherosomes and glycosomes, elongation of stipulodes and development of active branch dactyls. Spring branch inter‐nodes were characterized by high plasmalemma PDs (–210·5±30·8mV; [K+]o 0·5 mol m−3; pH 7·6), predominantly active, non‐isolated dactyls (spinaceous tips), and extensive intercellular communication (frequency of intercellular transport of 6 carboxyfluorescein = 89·2%). Artificial elevation of the intracellular calcium ion concentration by application of ionophore A23187 or Ca2+ microinjection significantly restricted intercellular communication to a level similar to that found in winter. The depression of intercellular communication in winter tissues is suggested to be due to high sensitivity to action potentials and/or to Ca2+ fluxes. Changes in intracellular Ca2+ distribution may be involved in the transition between the morphologically distinct states of dormancy and incipient fertility.

Antigen reduces nasal transepithelial electric potential differences and alters ion transport in allergic rhinitis in vivo.

The change of ion transport in acute allergic reactions in vivo was studied by measuring the nasal transepithelial potential difference (PD) in patients with nasal allergy to Japanese cedar pollens. Comparison of nasal PD in the pollen season revealed a lower PD in the allergic patients than in the normal control subjects. We challenged the patients with allergen in the non-pollen season and measured the time course change of nasal PD and rate of inhibition of PD by amiloride and indomethacin. Nasal PD reached the lowest value 15 min after nasal allergen challenge. Percent inhibition of PD by amiloride was greater without the allergen challenge than it was in those patients after allergen challenge (51.7% versus 29.4%, p less than 0.01). Indomethacin did not change PD without allergen challenge, whereas it depressed nasal PD by 25.1% after allergen challenge. These results suggest that decreased sodium absorption and increased chloride secretion occur in local allergic reactions. Both changes may contribute to the increase in fluid transport towards the lumen, and this may lead to abnormalities of nasal secretion during acute allergic reactions.

Electrospray ionization for analysis of platelet‐activating factor

Platelet-activating factor (PAF) was analyzed by electrospray-ionization mass spectrometry (ESI-MS) using a single quadrupole mass spectrometer. The positive-ion spectrum was dominated by an ion corresponding to a sodiated molecule when a low potential difference between the capillary exit (nozzle) and the skimmer was employed, but when the capillary exit voltage was increased, fragmentation of PAF was observed. Initial fragmentation involved the loss of the elements of trimethylamine from the sodiated molecule to yield [M+Na-59]+. An intense ion at m/z 147, generated by the loss of trimethylamine from the sodiated phosphocholine portion of the molecule was also detected, along with a lower intensity ion at m/z 184 which is representative of a protonated phosphocholine moiety. With negative-ion detection the major molecular species was [M+Cl]-. Interpretation of the mass spectral fragments was verified by ESI tandem mass spectrometry on a triple-quadrupole tandem mass spectrometer.

Gestational changes in electrolyte transport, electrical activity, and permeability of the porcine placenta

1. The electrolyte transport capacities of the porcine placenta and fetal membranes (amnion, chorion, and allantois) during gestation (47-112 days) were assessed in vitro and in the absence of electrochemical, osmotic, or hydrostatic driving forces. Net transmural transport of 22Na and 36Cl across sections of porcine allantochorion-endometrium (ALCE), amniochorion-endometrium (AMCE), and allantoamnion (AA) mounted in Ussing chambers could not be detected at any stage of gestation. 2. These tissues were characterised throughout gestation by low electrical potential difference (PD; less than 5 mV, fetal side positive with respect to maternal side) and short circuit current (SCC; less than 16 microA.cm-2) which were amiloride and iodoacetate sensitive. 3. A periparturitent reversal in the polarity of PD to fetal side negative and a change in the direction of the SCC was observed in tissues obtained from sows (n = 3) at 111-112 day gestation. These changes were accompanied by a 73% increase in electrical resistance (R) and a 2-10-fold decrease in the permeability of tissues to Na and Cl. 4. Morphological studies revealed a decrease in the thickness of allantoamnion and a decrease in the height of epithelia from ALCE, AMCE, and AA during gestation, indicating a decrease in activity. These morphological changes only partly explained the pre-term electrophysiological changes in these tissues.

Effect of heart-lung transplantation on airway potential difference in patients with and without cystic fibrosis

Measurement of the potential difference (PD) across the airways provides an indication of the viability and integrity of the lining epithelium. PD was recorded from the lower airways in "diseased controls" and in patients following heart-lung transplantation. Diseased controls showed a high PD centrally which fell (became less negative) peripherally (trachea -15.8 mV (SEM 1.0), lobar bronchi -12.6 mV (1.2), segmental bronchi -9.8 mV (1.2]. Following heart-lung transplantation (HLT) the profile of PD with airway size was altered in comparison to non-transplanted patients with reduced values in the large airways. Host tracheal values above the anastomosis were similarly reduced. Two episodes of rejection were associated with a lower mean airway PD; no significant changes were found with infection. In patients with cystic fibrosis (CF), values in the donor lung did not differ from those in non-CF transplanted patients up to one year following transplantation, although nasal PD in the host remained elevated. HLT selectively alters the PD profile only of larger airways, which may relate to the interruption of the bronchial arterial supply to these sites.

ウサギ鼻粘膜の電気的特性

The water flow across the respiratory epithelia is an important determinant of the efficiency of mucociliary clearance. Bulk water flow has been shown to be coupled to net ion flux. We studied ion transport across rabbit nasal mucosa by measuring bioelectric properties using Ussing chambers. Results were summarized as follows. (1) Compared with tracheal mucosa, nasal mucosa exhibited lower potential difference (p less than 0.01), lower short-circuit current (p less than 0.05), and higher conductance (p less than 0.01). (2) Ouabain 10(-4)M inhibited short-circuit current when added to the submucosal bath of Ussing chambers, and amiloride decreased short-circuit current to about 40% when added to the mucosal bath. (3) When the bubbling of the solution was changed from 95%O2, 5%CO2 to 100%N2, short-circuit current remarkably decreased. (4) A significant positive correlation existed between temperature ranging from 33 degrees C to 41 degrees C and short-circuit current (r = 0.46, p less than 0.02).

Aqueous two-phase polymer partitioning of lipid vesicles of defined size and composition

The kinetics of the partitioning of lipid vesicles containing acidic phospholipids in aqueous two-phase polymer systems are dependent upon the vesicle size; the larger the vesicles, the more readily they adsorb to the interfaces between the two polymer phases and hence are cleared from the top phase as phase separation proceeds. The partitioning of neutral lipid vesicles is principally to the bulk interface and is the same in phase systems of both low and high electrostatic potential difference between the two phases (Δψ). The incorporation of negatively charged lipids has two effects upon partition. First, vesicles with negatively charged lipids exhibit increased bottom phase partitioning in phases of low Δψ due to an enhanced wetting of the charged lipids by the lower phase. Second, the presence of a negatively charged group on the vesicle surface results in increased partition to the interface and top phase in phase systems of high Δψ. Differences observed in the partition of vesicles containing various species of negatively charged lipid thus reflect a competition between these two opposing factors.

20 MECHANISMS OF TRANSPORT OF SODIUM AND CHLORIDE AND THE EFFECTS OF INFLAMMATION IN THE HUMAN INFANT COLON

A major function of the colon is the conservation of salt and water and we have previously shown (Jenkins et al GUT 27; 1283, 1986) that in the human infant it plays a major homeostatic role. Colitis may therefore assume greater importance than in later life. We have carried out a detailed study of transport in normal and inflammed isolated human infant colon using an Ussing Chamber and a voltage clamp procedure. Stripped colonic mucosa histologically normal n=6 pairs and inflammed from patients with non-clostridial Hirschsprung's enterocolitis, n=5 pairs was mounted and bathed in Krebs2 solution. Under short-circuit conditions Na+ (3.45±1.53 umol/hr/cm mean ± ISD) and Cl−(0.63±3.61) were absorbed and a residual ion flux consistent with HCO3− secretion approximated Cl− absorption. Short circuit current (ISC) (3.8±0.28) was very similar to net Na+ movement and was markedly reduced by mucosal 10−4 M amiloride (0.61±0.7 p<0.01). Inflammed mucosa generated a lower potential difference (2.44±0.1 vs 6.5±1.0 m V p<0.01) ISC (1.62 ± 0.8 vs 3.87±0.5 p<0.02) and was of lower resistance (67.2±12 vs 104±10 chm p<0.01). Na+ was secreted and anion exchange reversed due to large increases of serosal to mucosal fluxes (Na+ 5.63±0.1 to 15.7±1.2 Cl− 13.86±1.614 to 20.9±3) with no change in nucosal to serosal fluxes. These data show that Na+ is absorbed electrogenically and Cl− electroneutrally in exchange for HCO3. In the presence of inflamnation the electrical and flux changes suggest a decrease in resistance of shunt pathways which dissipate absorbed Na+ and CT−. Inflammation of the infant colon therefore seriously impairs its ability to conserve salt and water, and would thus make an important contribution to a dehydrating diarrhoeal disease.

Relationship between rectal mucosal prostaglandin production and water and electrolyte transport in ulcerative colitis.

We have used in vivo rectal dialysis to test the hypothesis that the diarrhoea of patients with active ulcerative colitis (UC) is due to inhibition of large intestinal salt and water absorption by enhanced local mucosal prostaglandin (PG) synthesis. In 28 patients with untreated UC, increased rectal mucosal PGE2 release varied inversely with sodium transport and directly with potassium transport; higher PGE2 release was also associated with lower (i.e. less negative) potential difference (PD). Disease activity assessed sigmoidoscopically was positively related to PGE2 release, potassium transport and lower PD. Similar relationships were found in 33 patients treated with sulphasalazine and/or corticosteroids and in 9 patients studied serially when on unaltered conventional, or no treatment. In contrast, when 10 patients with UC were given the PG synthesis inhibitor, flurbiprofen, a significant fall in PGE2 release was associated with deteriorations in mucosal PD and transport of sodium and potassium. Increased PG production is therefore unlikely to be a major determinant of the abnormalities of electrolyte transport found in UC. The correlations between mucosal PGE2 release and electrolyte transport were probably due to the relationship of these variables with some other consequence of tissue damage.

The performance of conduits in grounding circuits

Rigid steel, thin-walled steel and aluminium conduits are investigated for their effectiveness in minimizing shock hazard under fault conditions. This analysis considers two extreme cases of internal and external current return paths which exhibit markedly different characteristics. Current distribution in, and potential difference along, the conduit wall also depend on its thickness and permeability. The longitudinal potential difference in rigid steel conduit is considerably larger for external current return paths than for aluminium or thin walled steel conduit. The use of rigid steel conduit grounded before entry to the area may reduce the hazard in installations where even a low potential difference can be hazardous, such as in patient care areas and operating theatres of hospitals. A multiple-bonded conduit may increase the hazard through an increased surface potential gradient.

Further studies on sudden potential drop in gastric mucosa.

The sudden potential drop (SPD) with its associated resistance drop, previously noted during anoxia when serosal pH was slightly decreased, can also be produced by substrate deprivation and reversed by addition of substrate. During a critical portion of the response, alternate stable high and low potential difference states can be selected by current pulsing. High Ca2+ in the serosal solution prevents the SPD response, and any condition preventing an SPD response will reverse the post-SPD potential. Although pH 1 mucosal solutions do not damage the tissue, an SPD under these conditions results in permanent loss of secretory activity, apparently due to increased H+ permeability in the post-SPD state. Cl-, Rb+, and urea fluxes are unchanged by the SPD. Since gastric anoxia and mild serosal acidosis might be expected during strong sympathetic stimulation, it is notable that an SPD can be produced in vivo by anoxia or vasoconstrictive drugs under conditions apparently in agreement with the in vitro requirements. This might provide a model system for studies of stress ulcer production. An equivalent circuit model for the SPD is presented, which agrees satisfactorily with the observations.