Changes In Potential Difference Research Articles

Submucosal plexus alone integrates motor activity and epithelial transport in rat jejunum

It has been well established in several mammalian species, including humans, that contractions of jejunal smooth muscle correlate temporally with increases in mucosal ion transport. Furthermore, this correlation is abolished through local application of neurotoxins, suggesting interaction of enteric neurons. The purpose of this study was to determine whether the myenteric plexus is involved in this correlation. In the rat jejunum in vivo, we simultaneously measured phasic changes in intraluminal pressure and transmural potential difference (PD) as indicators of smooth muscle motor activity and epithelial ion transport, respectively. We compared the temporal association of these parameters in control animals with animals in which either the extrinsic nerves only or the extrinsic nerves and the myenteric plexus of a 5-cm jejunal segment had been ablated 30 days previously. A one-to-one coupling between muscle contractions and transmural PD fluctuations was observed in all animals; ablation of the extrinsic and/or myenteric neurons did not eliminate this correlation. We conclude that, in the rat jejunum, the submucosal plexus alone can integrate the reflex that couples ion secretion to muscle contraction.

Luminal responses to bradykinin on the isolated canine tracheal epithelium: effects of bradykinin antagonists

We have tested the ability of several B 2 antagonists on the responses of the open-circuited isolated canine tracheal epithelium to the luminal addition of Bradykinin (BK), Lys-BK, and substance P (SP). All three peptides produced biphasic changes in transmural potential difference (PD), an initial decrease (dip) followed by an increase (rise). The B 2 antagonists d-Arg o [Hyp 3,Thi 5,8, d-Phe 7]BK (B5630) reversibly inhibited both the dips and the rise with IC 50 values of 2.01 · 10 −8 and 1.54 · 10 −7 M, respectively. The responses to SP were unaffected even with high concentrations of the antagonist. Other antagonists tested [ d-Phe 1,7,Thi 5,8]BK (B4158), [ d-Phe 2,7]BK (B4404), and [ d-Phe 7,Hyp 8]BK (B5092) were ineffective.

Comparison of the damage-promoting effects of leukotrienes derived from eicosapentaenoic acid and arachidonic acid on the rat stomach.

The ability of leukotrienes derived from eicosapentaenoic acid were compared with counterpart leukotrienes derived from arachidonic acid in terms of their ability to affect susceptibility of the stomach to injury induced by a topical irritant and their ability to alter gastric blood flow. Intra-arterial infusion of leukotriene C4 (LTC4) and LTD4 (0.1-3 micrograms/kg/min for 5 min) produced dose-dependent increases in gastric mucosal damage induced by topically applied 20% ethanol, as assessed macroscopically, by changes in transmucosal potential difference and by measurement of efflux of protein into the gastric lumen. Similar doses of LTC5 or LTD5 did not produce significant changes in any of these three parameters, when compared with control rats receiving the vehicle. With a higher dose of LTC5 or LTD5 (5 micrograms/kg/min), significant damage was observed. LTC4 and LTD4 were also found to be more potent at reducing gastric blood flow than LTC5 and LTD5. These results demonstrate that the peptido-leukotrienes derived from eicosapentaenoic acid (LTC5 and LTD5) are on the order of five times less potent than the leukotrienes derived from arachidonic acid (LTC4 and LTD4), in terms of increasing the susceptibility of the gastric mucosa to damage and reducing gastric blood flow. These results may have important implications in terms of the hypothesis that fish oil diets may be protective or may accelerate healing in ulcerative diseases of the gastrointestinal tract.

Transepithelial electrical responses to sodium and potassium of nonsensory region of gerbil utricle

Sheets of utricular epithelium from gerbil were mounted in a micro-Ussing chamber. Step changes in [Na] and [K] on each side of the epithelium led to changes in transepithelial potential difference ( V t ) and resistance ( R t ) which were consistent with the presence of ionic conductances for these two ions. Responses of V t , to 20 mM Rb steps were similar to those to 20 mM K steps. Several common Na and K channel blockers were applied: No evidence for the presence of amiloride-sensitive Na channels was found. At 10 −6 M, amiloride caused no significant changes in V t but at 10 −3 M it initially decreased or increased V t when applied from the apical or the basolateral side, respectively. Ba and quinidine each reduced V t , quinidine more strongly from the basolateral than from the apical side. Tetraethylammonium, another K channel blocker, had no significant effect from either side. These data suggest that in spite of the low value of ( R t ), the cellular pathway contributes significantly to the voltage response to cation concentration steps in this epithelium. The mode of action of 10 −3 M amiloride and the K channel blockers remains uncertain.

Bicarbonate and DIDS effects on intracellular potential difference in rabbit ciliary epithelium

A change of [HCO3-] in the solution bathing isolated rabbit ciliary epithelium from 30 mM to 0, or vice versa, resulted in a change of intracellular electrical potential difference (PDI) of 7 mV. Intermediate [HCO3-] (5, 10 and 15 mM) solutions were also tested. No perceivable change of PDI occurred when [HCO3-] changed from 30 to 15 mM. PDI depolarized gradually when [HCO3-] decreased from 30 or 15 mM to 0 mM, but PDI hyperpolarized at a faster rate when [HCO3-] increased from 0 to 15 or 30 mM. The amount of change of PDI from 15 to 5 mM, or vice versa, and from 10 to 0 mM or vice versa, was 4 mV. The stilbene, DIDS (10(-4) M), hyperpolarized the PDI in HCO3(-)-rich solutions. The response of DIDS was reduced in HCO3(-)-free medium and inhibited in Cl(-)-free solution. The results suggest the existence of an electrogenic bicarbonate transport or Na+/HCO3- cotransport system.

Effects of 12-Sulfodehydroabietic Acid Monosodium Salt (TA-2711), a New Anti-Ulcer Agent, on Gastric Mucosal Lesions Induced by Necrotizing Agents and Gastric Mucosal Defensive Factors in Rats

AbstractEffects of TA-2711 on gastric mucosal lesions induced by various necrotizing agents and several defensive factors of gastric mucosa were investigated in rats. Oral administration of TA-2711 at 12.5 to 200 mg/kg prevented the formation of gastric mucosal lesions induced by 99.5% ethanol, 0.6 N HCl, 0.2 N NaOH and boiling water with ED50 values of 24, 58,16 and 101 mg/kg, respectively. Oral TA-2711 at 100 mg/kg increased the gastric mucosal prostaglandin E2 (PGE2) level without any change in transmucosal potential difference. A sustained decrease in gastric mucosal blood flow produced by intragastric administration of 99.5% ethanol was inhibited by oral TA-2711 (50,100 mg/kg) and 16, 16-dimethyl PGE2 (10 μg/kg). The effect of TA-2711 on ethanol-induced decrease in blood flow was suppressed by Indomethacin (10 mg/kg, s.c). Oral TA-2711 (25–100 mg/kg) dose-dependently increased the amount of mucus adherent to the gastric mucosa. In addition, gastric HCO3- secretion was increased by intragastric TA-2711 at 2.5 and 5.0 mg/ml. These results suggest that TA-2711 enhances gastric mucosal resistance by increasing mucus and HCO3- secretion and by maintaining mucosal blood flow, and protects the gastric mucosa against various irritants. The effects of TA-2711 appear to be mediated by mucosal prostaglandins such as PGE2.

Studies of cholera toxin‐induced changes of alkaline secretion and transepithelial potential difference in the rat intestine in vivo

A pH-stat technique was used to investigate the effects of cholera toxin (CT) on alkaline secretion from denervated intestines (jejunum, ileum, colon) in anaesthetized rats. Transepithelial potential difference (PD) was also followed in some experiments. CT, given intraluminally, caused a marked increase in jejunal alkaline secretion, whereas only a small effect was observed in the ileum and no apparent effect was noted in the proximal colon. The pronounced increase in jejunal alkaline secretion was found to be inhibited by 10-25% by hexamethonium (10 mg kg-1 body wt i.v.) and similarly by serosal application of lidocaine, whereas atropine (0.25 mg kg-1 body wt i.v.) had no effect. Thus the cholera toxin-induced alkaline secretion in the jejunum is attributed mainly to a non-nervous mechanism. The small effect of CT on ileal alkaline secretion observed in this study contrasts with the high ileal bicarbonate concentration reported in cholera by authors who estimated the concentration from the total carbon dioxide/bicarbonate contents. This discrepancy may be explained by a CT-evoked increased transport of the coupled Na+/H+ and Cl-/HCO3- exchangers, which cannot be measured with the pH-stat technique used in this study.

Effects of 12-sulfodehydroabietic acid monosodium salt (TA-2711), a new anti-ulcer agent, on gastric mucosal lesions induced by necrotizing agents and gastric mucosal defensive factors in rats.

Effects of TA-2711 on gastric mucosal lesions induced by various necrotizing agents and several defensive factors of gastric mucosa were investigated in rats. Oral administration of TA-2711 at 12.5 to 200 mg/kg prevented the formation of gastric mucosal lesions induced by 99.5% ethanol, 0.6 N HCl, 0.2 N NaOH and boiling water with ED50 values of 24, 58, 16 and 101 mg/kg, respectively. Oral TA-2711 at 100 mg/kg increased the gastric mucosal prostaglandin E2 (PGE2) level without any change in transmucosal potential difference. A sustained decrease in gastric mucosal blood flow produced by intragastric administration of 99.5% ethanol was inhibited by oral TA-2711 (50, 100 mg/kg) and 16,16-dimethyl PGE2 (10 micrograms/kg). The effect of TA-2711 on ethanol-induced decrease in blood flow was suppressed by indomethacin (10 mg/kg, s.c.). Oral TA-2711 (25-100 mg/kg) dose-dependently increased the amount of mucus adherent to the gastric mucosa. In addition, gastric HCO3- secretion was increased by intragastric TA-2711 at 2.5 and 5.0 mg/ml. These results suggest that TA-2711 enhances gastric mucosal resistance by increasing mucus and HCO3- secretion and by maintaining mucosal blood flow, and protects the gastric mucosa against various irritants. The effects of TA-2711 appear to be mediated by mucosal prostaglandins such as PGE2.

Interfacial potential difference for the liquid/liquid ion partition process

Abstract Studies of the equilibrium interfacial potential difference at the liquid/liquid interface and the kinetics of the ion partition process are presented. The standard formal potentials of TMA + (+ 0.044 V), TEA + (−0.051 V), picrate − (+0.042 V), ClO 4 − (−0.087 V), and MnO 4 − (−0.080 V) ions are determined by a new method and are consistent with the available published values. A theoretical model is described to account for the rate of change of the interfacial potential difference during the ion partition process. Such rates are dependent upon a number of factors such as the initial concentrations, the transfer rate constants, and the diffusion coefficients of transferring ions. A numerical method is used to calculate the interfacial potential values as a function of time according to several convolution equations. The measured interfacial potential-time curves are similar to the theoretically calculated ones. Thus, the model helps the understanding of mechanisms of interfacial ions transfer and the rate of change of interfacial potential difference. The ion transfer process is started by a fast interfacial ion transfer stage, followed by a transfer/diffusion combined stage, and ended by a slow diffusion stage.

Effect of bismuth subcitrate on amphibian gastroduodenal bicarbonate secretion.

The ulcer healing and cytoprotective properties of colloidal bismuth (De-Nol) are well established although its mode of action is unclear. We have examined the action of bismuth subcitrate, the active ingredient of De-Nol, on gastroduodenal bicarbonate secretion by isolated amphibian mucosa. Addition of bismuth subcitrate (10(-6) to 10(-4) M) to the luminal solution produced a dose dependent increase in bicarbonate secretion from both gastric and duodenal mucosae without a change in transmucosal potential difference. The magnitude of this stimulation was greater for gastric than duodenal mucosae at all dose ranges. A second bismuth salt, bismuth oxynitrate, produced similar increases in bicarbonate secretion from gastric mucosae. Pretreatment of gastric mucosa with the cyclooxygenase inhibitor, indomethacin (10(-5) and 10(-4) M), did not abolish the secretory response to bismuth subcitrate. Similar treatment with the chloride transport inhibitor, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) (10(-3) M) prevented the secretory response to bismuth subcitrate.

Effect of enprostil on amphibian gastroduodenal and human gastric bicarbonate secretion

The protective and ulcer healing properties of prostaglandins are well established. We have explored the possible mode of action of enprostil, a synthetic dehydroprostaglandin E2, on amphibian gastroduodenal mucosal bicarbonate secretion in vitro and on human gastric bicarbonate secretion in vivo. Addition of enprostil (10(-6) M) to the luminal solution of isolated amphibian gastric mucosa produced a 28% increase in bicarbonate secretion without a change in transmucosal potential difference. The same concentration of enprostil added to the luminal solution of isolated amphibian duodenal mucosa produced a 37% increase in bicarbonate secretion and was associated with a rise in transmucosal potential difference. The gastric output of bicarbonate from the human stomach has been calculated using a perfusion technique before, during, and after perfusion with enprostil (35 micrograms) in six healthy volunteers. A significant 78% increase in bicarbonate secretion occurred during the period of enprostil perfusion, falling to normal during the postenprostil period. These changes were caused mainly by an increase in gastric secretory volume with insignificant increases in bicarbonate concentration. These results suggest that stimulation of gastroduodenal bicarbonate secretion by enprostil may play a role in its protective actions.

Voltage-driven, taurocholate-dependent secretion in isolated hepatocyte couplets.

Bile formation by the liver is largely dependent on the transport of bile acids by hepatocytes. This process is thought to result from Na-coupled uptake of bile acids into the cell and voltage-dependent, carrier-mediated transport from cell to canaliculus. However, the dependence of bile secretion on membrane potential has not yet been observed. In this study, the effect of changes in membrane potential differences on bile secretion was tested by impaling rat hepatocyte couplets with microelectrodes, changing membrane potential by intracellular current injection, and measuring fluid secretion by optically determining canalicular size. In the presence of 50 microM taurocholate, membrane potential was -33.3 +/- 5.8 mV and canalicular area increased by 6 +/- 6%/min, corresponding to a fluid secretion rate of 2-4 fl/min. In contrast, when intracellular voltage was suddenly changed to -109.9 +/- 15.0 mV, the canalicular area increased by 20 +/- 4%/min, corresponding to a secretion rate of 19 fl/min. When these experiments were repeated in the absence of taurocholate, the negative clamp had no effect on canalicular size. Taurocholate itself did not alter membrane potential. These findings support the hypothesis that canalicular bile secretion depends on a process equivalent to electrodiffusion. We therefore conclude that membrane voltage is a driving force for taurocholate-dependent fluid secretion by the liver.

Photochemical ion transfer across the interface between two immiscible electrolyte solutions

Irradiation of the interface between two immiscible electrolyte solutions (ITIES) by visible or UV light can give rise to a photocurrent [l-3] or photopotential [4]. This effect has been ascribed either to the photoexcited electron transfer between a sensitizer in one solvent phase and an electron acceptor in the other solvent phase [1,3], or to the transfer of an ionic product of the homogeneous photoassociated electron transfer reaction [2]. Eventually, the non-radiative dissipation of the absorbed light can result in a microscopic thermal gradient at the ITIES bringing about a change in the interfacial potential difference - a sort of ~e~~lect~c effect [2]. The purpose of this communication is to show that the base electrolyte ions themselves can yield a photocurrent which is closely related to their excited states. This applies in particular to aromatic ions like tetraarylborate anions or tetraarylarsonium cations. The interface between water and 1,2-~chloroeth~e (geometric area of 2.5 cm2) was formed in an all-glass four-electrode cell [5], with the organic solvent phase placed in the bottom part of the cell. The top of the cell was left open, so that the light from a 150 W xenon arc source (Applied Photophysics, Model 4060) reflected by a mirror at 45’ passed only through the layer of the non-absorbing aqueous phase prior to reaching the interface. Mon~hromatic light was obtained from a monochromator (Applied Photophysics) placed between the xenon lamp and the reflection mirror. The incident intensity of the monochromatic light was measured by means of a calibrated photodiode detector (Macam Photometrics, Model SD

Integer charge transport in Josephson junctions.

We describe a macroscopic demonstration of quantized adiabatic transport coefficients using superconductors coupled by Josephson junctions. The transport coefficients relate charges and currents to changes in potential differences and loop fluxes. They have geometrical significance and quantized average related to first Chern characters.

Effects of UV‐C radiation on extension growth, H+‐extrusion and transmembrane electric potential in maize coleoptile segments

The effect of 253.7 nm ultraviolet radiation on elongation growth, medium acidification and changes in electric potential difference between vacuole and external medium in cells of maize (Zea mays L.) coleoptile segments was investigated. It was found that irradiation with 390, 1170, 3900 and 5 850 J m−2 UV‐C (ultraviolet radiation 253.7 nm) inhibited elongation growth, whereas at 195 J m−2 stimulation of growth was observed. The administration of IAA (10−5M) to the incubation medium of coleoptile segments partially abolished the inhibitory effect of UV‐C. The pH of the incubation medium, measured simultaneously with growth, showed that the exposure of the segments to UV‐C caused inhibition of H+‐extrusion (or stimulation of H+ uptake). The presence of IAA (10−5M) in the incubation medium promoted (except after 5850 J m−2 irradiation) H+‐extrusion to a level comparable with that produced by IAA in non‐irradiated segments. In UV‐C irradiated segments the potential difference underwent significant alterations. Irradiation of coleoptile segments with 390 J m−2 caused a transient depolarization, which was fully reversible within 30 min, while at higher doses depolarization was irreversible. The hyperpolarization of the membrane potential (MP) in cells of maize coleoptile induced by IAA was completely nullified by subsequent irradiation with UV‐C. It is suggested that UV‐C inhibited IAA‐induced growth by a mechanism independent of cell wall acidification.

Interactions Between Hemolytic Saponins, Bile Salts and Small Intestinal Mucosa in the Rat

The interaction between bile salts and saponins from Gypsophylla was investigated in vitro, using changes in transmural potential difference across isolated lengths of rat jejunum as an index of the capacity of the saponin to affect the permeability of intestinal mucosal cells. The addition of saponin (ca. 5 mM) to taurocholic acid in buffered saline (pH 7.4) led to a significant increase in viscosity, indicating the formation of a polymer. The viscosity of the solution was highest at low molar ratios of bile salt to saponin (0.5-2.0). Under these conditions there was an inhibition of the permeating effect of saponins on the gut, as judged by the rate of decline in transmural PD. There was no evidence of inflammation or functional damage to the jejunal mucosa of rats fed a diet containing Gypsophylla saponin (ca. 1.5% w/w) for 7 d but changes in villus morphology were observed. There was also evidence of an increased rate of mucosal cell proliferation. Serum cholesterol levels were significantly lower in saponin-fed rats than in controls, while the cholesterol content of the cecal contents was increased. These results suggest that despite the protective effect of bile salts, Gypsophylla saponins interact with the mucosa of the proximal small intestine in vivo, but at the dietary level used in this study the mucosa was protected by an enhanced rate of cell replacement. The loss of cholesterol via exfoliated mucosal cells may contribute to the hypocholesterolemic effect of saponins in rats.

A submucosal mechanism for catecholamine-induced increases in fluid absorption in rabbit ileum in vitro.

1. The effects of clonidine and dopamine on water movements across the mucosal and serosal surfaces of rabbit ileum have been investigated using a high-resolution method for monitoring water flows in vitro. 2. Theophylline (10 mM) and carbamyl choline (10 microM) caused a reduction in fluid inflow across the mucosal surface and a smaller decrease in fluid outflow across the serosal surface. Addition of the alpha 2-adrenergic agonist clonidine or dopamine fully reversed the theophylline, or carbamyl choline-induced decrease in mucosal inflow in a dose-related manner. 3. The effects of clonidine on mucosal inflow are blocked by the alpha 2-adrenergic antagonist, yohimbine. Yohimbine was much less effective than pimozide or d-butaclamol in blocking the effect of dopamine on mucosal inflow. These findings support the view that there are separate alpha 2-adrenergic and dopaminergic receptors. 4. The hydraulic conductance (Lp) of the serosal surface was measured directly from the change in serosal exit flow following addition of 2 mosmol kg-1 of polyethylene glycol (molecular mass 20,000 Da) to the serosal bathing solution. Theophylline reduced the Lp by 35%. Clonidine (1 microM) added to theophylline-treated tissues increased the Lp by 66%. This effect was prevented by yohimbine (1 microM). 5. The effects of theophylline, clonidine and dopamine on the permeability of the mucosal and serosal surfaces of the tissue to [3H]mannitol were measured. These showed that theophylline increased the rate of labelled mannitol loss across the mucosal surface but reduced the mannitol permeability across the serosal surface. This latter effect was reversed by clonidine and dopamine. 6. Changes in transepithelial electrical potential difference (PD), short-circuit current and resistance were monitored. Theophylline caused a rapid increase in PD and short-circuit current and a slower increase in resistance. Clonidine (5 microM) reversed the effects on PD and resistance but was without significant effect on short-circuit current. The results suggest that a major component of secretagogue-induced reduction in fluid transport in vitro is due to mechanical changes in the submucosa, probably induced by modulation of neurotransmitter release within the tissue.

Metabolic Dependence of Na + Efflux from Roots of Intact Maize Seedlings

Summary The mechanism of Na+ efflux from roots was investigated using intact seedlings of Zea mays L. cv. Pioneer 3906. 22Na+ efflux was independent of external Na+ but stimulated by K+. Low temperature (4°C) and the Ca2+ chelator, ethyleneglycol-bis-(β-aminoethyl ether) N,N1,N1-tetraacetic acid (EGTA), increased 22Na+ efflux. The protonophore and uncoupler, carbonylcyanide-3-chlorophenylhydrazone (CCCP), and the sulfhydryl reagent, N-ethylmaleimide (NEM), did not affect 22Na+ efflux during the initial 60 minutes. Except for Na+, which transiently depolarized the membrane potential, a permanent depolarization was observed with all treatments, causing a change in the electro-chemical driving force for Na+. The data allowed to distinguish between two cytoplasmic Na+ efflux components: an active component depending on metabolic energy and a passive one driven by the electro-chemical potential difference for Na+. Since both components counteract each other when metabolism is inhibited (e.g. by CCCP or NEM), metabolic dependence of Na+ efflux from maize roots can only by estimated indirectly taking into account the change in the electro-chemical potential difference for Na+.

Adaptive cytoprotection by 0.25 M HCl is truly "cytoprotective" and may not depend upon elevated levels of prostaglandin synthesis.

The ability of a mild irritant to reduce ethanol-induced damage to the rat gastric mucosa was investigated using an ex vivo gastric chamber preparation. Exposure to 0.25 M hydrochloric acid (HCl) did not cause significant damage to the surface epithelium, but did reduce both the lesion area and the extent of superficial epithelial damage caused by subsequent exposure to 40% ethanol (EtOH). "Adaptive cytoprotection" was also demonstrated by the reduction of ethanol-induced changes in transmural potential difference and net K+ efflux, and by rapid recovery of these physiological parameters following the removal of ethanol from the chamber. Pretreatment of rats with indomethacin at a dose that has been shown to significantly inhibit gastric cyclooxygenase activity did not significantly affect the ability of 0.25 M HCl to reduce the effects of ethanol on lesion area, epithelial damage, potential difference, and net K+ efflux.

Stimulation of amphibian gastroduodenal bicarbonate secretion by sucralfate and aluminium: role of local prostaglandin metabolism.

The present studies were designed to explore the possible mode of protective and ulcer healing actions of sucralfate by examining its effect on gastroduodenal bicarbonate secretion by isolated amphibian mucosa. Luminal sucralfate (0.5 g/l) significantly increased bicarbonate secretion by fundic and antral mucosa without influencing transmucosal potential difference. Significant stimulation of duodenal bicarbonate secretion occurred only at 1.0 g/l without change in potential difference. Aluminium, a component of sucralfate, produced similar increases in bicarbonate secretion, while the sucrose and sulphate components were without effect. Pretreatment of mucosae with the cyclooxygenase inhibitor, indomethacin (10 5M) did not abolish the secretory response to sucralfate or aluminium. The results suggest that stimulation of gastroduodenal bicarbonate secretion, possibly by the aluminium moiety of sucralfate, may play a role in its protective and ulcer healing actions.