Increase In Chloride Permeability Research Articles

The vagus and the heart: revisiting an early contribution to a still on-going dispute

The vagus and the heart: revisiting an early contribution to a still on-going dispute

Role of Datscan and Clinical Diagnosis in Pd

Interleukin-1 (IL-1), a cytokine involved in the acute phase reaction to injury and infection, has multiple effects in the central nervous system, including induction of fever and sleep and the release of several neuropeptides. We evaluated effects of IL-1 beta on inhibitory postsynaptic function at the gamma-aminobutyric acidA (GABAA) receptor. IL-1 (100 pg/ml to 10 ng/ml) augmented GABAA receptor function in cortical synaptic preparations. This effect of IL-1 was largely prevented by incubation with a specific IL-1 receptor antagonist. The related cytokines interleukin-6 and tumor necrosis factor did not augment GABA-dependent chloride transport. Similar enhancement of GABAA receptor function was observed in tissue prepared from mice previously injected intraperitoneally with IL-1 (1 microgram). Electrophysiological studies in cultured primary cortical neurons demonstrated that IL-1 enhanced the GABA-mediated increase in chloride permeability, whereas IL-1 alone produced no alterations in resting conductance. Behavioral studies indicated that IL-1 is similarly active in vivo; mice treated with IL-1 showed a decrease in open-field activity and an increase in the threshold for pentylenetetrazol-induced seizures. The interaction of IL-1 with GABAA receptors might account for the somnogenic and motor-depressant effects of this cytokine.

A comparative study of the inhibitory effects of purine nucleotides and carboxyatractylate on the uncoupling protein-3 and adenine nucleotide translocase.

Uncoupling proteins (UCPs) mediate fatty acid-induced proton cycling in mitochondria, which is stimulated by superoxide and inhibited by GDP. Fatty acid anions can also be transported by adenine nucleotide translocase (ANT), thus resulting in the uncoupling of oxidative phosphorylation. In the present work, an attempt was made to distinguish between the protonophoric activity of UCP3 and that of ANT using inhibition analysis. This study was carried out using mitochondria from skeletal muscles of hibernating Yakut ground squirrel, which have a significant level of UCP3 mRNA. We found that millimolar concentrations of GDP, which is considered to be a specific inhibitor of UCPs, slightly recoupled the mitochondrial respiration and restored the membrane potential. Addition of the specific ANT inhibitor CAT (carboxyatractylate), in micromolar concentration, prior to GDP prevented its recoupling effect. Moreover, GDP and ADP exhibited a competitive kinetic behavior with respect to ANT. In brown adipose tissue, CAT did not prevent the UCP1-iduced increase in chloride permeability and the inhibitory effect of GDP, thus confirming the inability of CAT to affect UCP1. These results allow us to conclude that the recoupling effect of purine nucleotides on skeletal muscle mitochondria of hibernating ground squirrels can be explained by interaction of the nucleotides with ANT, whereas UCP3 is not involved in the process.

An investigation into the influence of inter-aggregate spacing and the extent of the ITZ on properties of Portland cement concretes

Conventionally-designed concretes were prepared with different sand particle size distributions, so as to systematically vary the extent of aggregate-cement paste interface and the mean spacing between sand grains. The range of fineness modulus of the sands fully encompassed the range of sands normally used in concretes. The concretes were batched at w/c ratios of 0.30 and 0.50 and cured for various periods before carrying out determinations of mechanical properties and of “rapid chloride permeability”. The conventional notions of the effect of the ITZ on concrete properties would predict that a reduction in strength and an increase in chloride permeability would accompany increased ITZ interfacial area and closer spacing between sand grains. In general, no such influence was found. It appears from this research that the traditional notions of the adverse influence of the ITZ on the properties of conventional concretes may not be accurate, within the realms of conventional concrete and typical inter-aggregate spacings.

Maturation of rat proximal tubule chloride permeability

We have previously shown that neonate rabbit tubules have a lower chloride permeability but comparable mannitol permeability compared with adult proximal tubules. The surprising finding of lower chloride permeability in neonate proximals compared with adults impacts net chloride transport in this segment, which reabsorbs 60% of the filtered chloride in adults. However, this maturational difference in chloride permeability may not be applicable to other species. The present in vitro microperfusion study directly examined the chloride and mannitol permeability using in vitro perfused rat proximal tubules during postnatal maturation. Whereas there was no maturational change in mannitol permeability, chloride permeability was 6.3 +/- 1.3 x 10(-5) cm/s in neonate rat proximal convoluted tubule and 16.1 +/- 2.3 x 10(-5) cm/s in adult rat proximal convoluted tubule (P < 0.01). There was also a maturational increase in chloride permeability in the rat proximal straight tubule (5.1 +/- 0.6 x 10(-5) cm/s vs. 9.3 +/- 0.6 x 10(-5) cm/s, P < 0.01). There was no maturational change in bicarbonate-to-chloride permeabilities (P(HCO3)/P(Cl)) in the rat proximal straight tubules (PST) and proximal convoluted tubules (PCT) or in the sodium-to-chloride permeability (P(Na)/P(Cl)) in the proximal straight tubule; however, there was a significant maturational decrease in proximal convoluted tubule P(Na)/P(Cl) with postnatal development (1.31 +/- 0.12 in neonates vs. 0.75 +/- 0.06 in adults, P < 0.001). There was no difference in the transepithelial resistance measured by current injection and cable analysis in the PCT, but there was a maturational decrease in the PST (7.2 +/- 0.8 vs. 4.6 +/- 0.1 ohms x cm2, P < 0.05). These studies demonstrate there are maturational changes in the rat paracellular pathway that impact net NaCl transport during development.

Developmental Changes in Proximal Tubule Tight Junction Proteins

We demonstrated previously that neonatal proximal tubules have a lower passive paracellular permeability to chloride ions and higher resistance than that of adult proximal tubules. In addition, administration of thyroid hormone to neonates, before the normal maturational increase in serum thyroid hormone levels, prematurely accelerates the developmental increase in chloride permeability to adult levels. To test the hypothesis that there is a maturational change in tight junction proteins and that thyroid hormone mediates these changes, we examined the two known tight junction proteins present in proximal tubules, occludin and claudin 2. Using immunoblot and immunohistochemistry, we demonstrated that claudin 2 has a 4-fold greater abundance in neonatal proximal tubules than in adult tubules. Occludin, however, has a 4-fold greater expression in adult tubules than in neonatal tubules. Administration of thyroid hormone to neonates did not affect claudin 2 expression, occludin expression, or the transepithelial resistance in rat proximal tubule cells in vitro. In conclusion, there are postnatal maturational changes in tight junction proteins. The factors that cause these maturational changes are unknown but unlikely to be due solely to the maturational increase in thyroid hormone.

Functional expression of p64, an intracellular chloride channel protein.

p64 is a protein identified as a chloride channel by biochemical purification from kidney microsomes. We expressed p64 in HeLa cells using a recombinant vaccinia virus/T7 RNA polymerase driven system. Total cell membranes were prepared from infected/transfected cells and fused to a planar lipid bilayer. A novel chloride channel activity was found in cells expressing p64 and not in control cells. The p64-associated activity shows strong anion over cation selectivity. Single channels show prominent outward rectification with single channel conductance at positive potentials of 42 pS. The chloride channel activity is activated by treatment of the membranes with alkaline phosphatase and inhibited by DNDS and by TS-TM calix(4)arene. Whole membrane anion permeability was determined by a chloride efflux assay, revealing that membranes from cells expressing p64 showed a small but highly significant increase in chloride permeability, consistent with expression of a novel chloride channel activity.

Glucose-stimulated sodium transport by the human intestine during experimental cholera

BACKGROUND & AIMS: Net sodium absorption from oral rehydration solution is increased by both glucose-sodium cotransport and solvent drag. The aim of this study was to measure the relative importance of glucose- sodium cotransport and solvent drag in the stimulation of net sodium absorption by oral rehydration solution. METHODS: Total intestinal perfusion was used in normal subjects with and without intrajejunal cholera toxin using three test solutions containing 100 mmol/L sodium and either 100 mmol/L mannitol (control), 100 mmol/L glucose, or no additional solute (hypotonic solution). The increase in sodium absorption greater than control with hypotonic solution represented sodium absorption stimulated by solvent drag; the further increase in sodium absorption induced by glucose, greater than that noted with the hypotonic solution, represented sodium absorption stimulated by cotransport. RESULTS: Without cholera toxin, solvent drag and cotransport promoted sodium absorption at rates of 62 and 33 mmol/h, respectively. With cholera toxin, solvent drag and cotransport promoted sodium absorption at rates of 44 and 71 mmol/h, respectively. CONCLUSIONS: Net sodium absorption caused by cotransport increased more than twofold after exposure of the intestine to cholera toxin (P < 0.003). This could be mediated by increased cotransport, a change in the stoichiometry of cotransport, or an increase in chloride permeability. (Gastroenterology 1997 May;112(5):1529-35)

Activation of ATP-sensitive potassium channels in follicle-enclosed xenopus oocytes by the epileptogenic agent pentylenetetrazol.

For further investigation of the epileptogenic properties of pentylenetetrazol (PTZ), membrane currents elicited by PTZ were analysed in native Xenopus oocytes. PTZ elicited a sequence of membrane currents. Two inward currents have been described to be due to a decrease in potassium permeability and an increase in chloride permeability. Experiments performed up to 3 days after preparation of the oocytes showed that PTZ is also able to activate an outward current. This current is: (1) reversed near the potassium equilibrium potential, (2) associated with a decrease in membrane resistance, (3) reduced by tetraethylammonium and caesium, (4) abolished by defolliculation, and (5) blocked by glibenclamide. Thus, the current can be interpreted to be due to an activation of ATP-sensitive potassium (KATP) channels located in the follicle cells. An activation of KATP channels by PTZ may contribute to termination and re-initiation of seizure activity.

Actions of Glycine on Non‐dopaminergic Neurons of the Rat Substantia Nigra

The effects of glycine on non-dopaminergic cells in rat substantia nigra pars compacta and pars reticulata maintained in vitro were investigated using intracellular recording techniques. Glycine, superfused at a concentration between 30 microM and 1 mM, reversibly blocked the spontaneous firing of these neurons. The inhibition of firing discharge was associated with a hyperpolarization of the membrane (potassium acetate-filled electrodes) and an increase in conductance. Under voltage-clamp experiments (holding potential between -57 and -65 mV), glycine produced an outward response which reversed polarity at about -74 mV. However, when the recording electrodes were filled with KCl, the glycinergic response was mainly depolarizing/inward and reversed at about -43 mV. Thus, it appeared to be due to an increase in chloride permeability. Furthermore, the effects of glycine were reversibly antagonized by strychnine (between 300 nM and 1 microM). Our findings demonstrate that glycine is a potent inhibitory agent on non-dopaminergic cells of the substantia pars compacta and par reticulata that acts by activating strychnine-sensitive receptors.

The actions of the catch relaxing peptide, carp, on identified Helix central neurons

1. The action of the catch relaxing peptide CARP (H-Ala-Met-Pro-Met-Leu-Arg-Leu-amide, AMPMLRL-amide) has been studied on Helix central neurons. 2. CARP, at thresholds of 1 nM or less, excited some cells while inhibiting others. CARP modulated the action of acetylcholine, e.g. at 10–100 nM CARP, the acetylcholine response was greatly reduced. 3. The inhibitory action of CARP is mediated through an increase in chloride permeability while CARP excitation was dependent on sodium and calcium. 4. The use of blocking agents suggested that CARP and acetylcholine acted on separate receptors.

Calcium-dependent chloride currents elicited by injection of ethanol into Xenopus oocytes

Electrophysiological techniques were used to study the response of native Xenopus laevis oocytes to intracellular injection and bath application of ethanol. Injection of ethanol produced dose-dependent transient inward currents accompanied by large current fluctuations, with estimated intracellular concentrations ranging from 10 to 300 mM. The response duration varied between 2 and 15 min, with an onset delay of 2–15 s. The inward current sometimes consisted of a fast and a slow component. Bath application of equivalent concentrations elicited similar but considerably smaller responses. The current showed a reversal potential of −2 ± 10 mV, corresponding to an increase in chloride permeability. The response was eliminated in the presence of low chloride saline and was blocked by the chloride channel inhibitors SITS and DIDS. Ethanol responses were inhibited by the intracellular injections of the calcium chelator EGTA and were unaffected when the extracellular calcium was lowered. It is concluded that ethanol injection into Xenopus oocytes elicits a release of calcium from intracellular stores, which then activates an increased membrane permeability to chloride.

Effects of GABA on CA3 pyramidal cell dendrites in rabbit hippocampal slices

Using the in vitro rabbit hippocampal slice preparation, we have investigated the effects of γ-aminobutyric acid (GABA) iontophoresis on CA3 pyramidal cell dendrites. The predominant response (70% of the cells tested) was hyperpolarization associated with a 30% decrease in cell input resistance ( R in). These hyperpolarizations displayed a very pronounced voltage dependency: they were decreased by cell depolarization and flattered by hyperpolarization. Bicuculline methiodide (BMI, 50 μM) did not abolish this response, nor did intracellular iontophoresis of chloride ions. In 5% of the cells, and additional hyperpolarization was obtained with longer ejection times; it reversed close to the reversal potential of the early component of the IPSP. In 25% of the cells, dendritic GABA application produced a depolarization. This response was reversed with cell membrane depolarization and was associated with a large (80%) decrease in R in. The depolarizations were abolished by BMI (50 μM) and greatly increased by increasing the intracellular chloride concentration. None of the responses to GABA were affected by blockade of synaptic transmission. We conclude that the predominant response of CA3 pyramidal cell dendrites to GABA application is a hyperpolarization mediated by GABA B receptors and probably carried by potassium ions. The depolarizing responses are mediated via GABA A receptors and depend on an increase in chloride permeability.

Increase in chloride permeability of snail neurons during high potassium-induced hyperpolarization.

High K+-induced hyperpolarization was recorded intracellularly from the snail neurons, Euhadra subnimbosa, and the ionic mechanism underlying this hyperpolarization was analyzed in comparison with the ACh-induced hyperpolarization of the same cell, the latter known to be Cl(-)-dependent. The membrane resistance always decreased during both hyperpolarizing responses to high K+ (24mM) and ACh (0.1 mM). Both hyperpolarizing responses to high K+ and ACh were reversed in Cl(-)-free Ringer to the depolarizing responses. Both hyperpolarizing responses to high K+ and ACh were markedly augmented immediately after returning to normal Cl- from Cl(-)-free Ringer perfusion. Increase in intracellular Cl(-)-concentration by a leak from KCl-electrode reversed both hyperpolarizing responses to high K+ and ACh. Reversal potential of high K+-response was always 10-20 mV more positive than that of ACh-response, when measured in normal Ringer perfusion. Intracellular Cl(-)-concentration of the cells which were hyperpolarized by high K+ was estimated to be one half of that of the cells which were depolarized by high K+. Above results indicated that the high K+-induced hyperpolarization is due to the permeability increase of the postsynaptic membrane toward Cl-, masking the depolarizing effect of high K+ on the same membrane.

The Glycine Receptor of Rat Spinal Cord: Exploring the Site of Action of the Plant Alkaloid Strychnine

AbstractThe amino acid glycine is a major neurotransmitter in the spinal cord of all vertebrates and is involved in the control of various motor and sensory functions. By binding to specific receptors of the neuronal plasma membrane, glycine produces an increase in chloride permeability and thus a hyperpolarization, i.e., an inhibition of glycine‐sensitive neurons. This inhibitory action of glycine is reversibly blocked by the plant alkaloid strychnine. We have used strychnine for the biochemical characterization and isolation of the glycine receptor of rat spinal cord. Our results show that the glycine receptor is a large membrane protein which contains three different polypeptides. Based on the currently available data we propose a structural model of the glycine receptor and discuss its relation to other proteins of the neuronal membrane that are involved in the transmission of nerve impulses.

Ramped voltage clamp study of the action of acetylcholine on three types of neurons in the snail ( Helix aspersa) brain

1. The ramped voltage clamp technique was developed as a rapid means of studying the ionic involvement and conductance changes during drug responses of Helix aspersa neurons. 2. Three types of identified neurons were found. (a) Hyperpolarized by ACh. This was due to an increase in chloride permeability. (b) Depolarized by ACh. This was due to an increase in sodium and chloride permeability. (c) Depolarized by ACh. This was due to an increase in sodium permeability. 3. The receptor-ionophores were of two types. Those linked to the Na-ionophore were blocked by hexamethonium. Decamethonium increased the chloride conductance. Strychnine and d-tubocurarine blocked the increased conductance to both sodium and chloride ions.

Effects of drugs on γ-aminobutyric acid receptors, uptake, release and synthesis in vitro

The effects of various convulsant and anticonvulsant drugs have been studied using in vitro assays for the postsynaptic action of the neurotransmitter γ-aminobutyric acid (GABA). GABA caused a receptor-ionophore mediated increase in chloride permeability in crayfish muscle. At 100 μ M concentrations, benzyl penicillin, bicuculline, diethyl barbiturate, diazepam, imipramine, and haloperidol partially inhibited this response while picrotoxinin inhibited it 100% (I 50 = 3 μ M). Muscimol (potently) andβ-( p-chlorphenyl) GABA (weakly) mimic GABA action in this assay. Muscimol and bicuculline (potent), and benzyl penicillin andβ-( p-chlorphenyl) GABA (weak), but not the other drugs, probably exerted their effects at the GABA receptor level, because only these four drugs among those tested were inhibitors of GABA receptor binding sites in mouse brain homogenates (sodium-independent sites having the specificity expected of receptor sites). Pentylenetetrazol weakly inhibited GABA receptor binding and GABA-induced chloride flux. Several other convulsants suspected of GABA antagonist activity, such as trimethyl caprolactam, isopropyl bicyclophosphate, tetramethylene disulfotetramine, and D-tubocurarine, showed no direct inhibition of either GABA receptor sites in mouse brain or of GABA-stimulated chloride flux in crayfish muscle. The drugs were also examined for effects on in vitro assays of GABA uptake, glutamate decar☐ylase activity (GAD), and Ca 2+-stimulated GABA release with mouse brain homogenates. GABA uptake by mouse brain particulate fractions was inhibited 50% by approximately 100μ M haloperidol, imipramine, chlorpromazine, diazepam, benzyl penicillin, bicuculline, andβ-( p-chlorophenyl) GABA, but by muscimol only at concentrations near1m M. Diazepam and benzyl penicillin also stimulated Ca 2+-independent efflux of GABA from mouse brain fractions enriched in synaptosomes. Diazepam, chlorpromazine, imipramine, and haloperidol inhibited Ca 2+-dependent release of GABA from brain particles enriched in synaptosomes. No drugs tested were found to inhibit L-glutamate decar☐ylase (GAD) activity at concentrations under100 μ M. The drugs diphenylhydantoin and diethyl barbiturate showed no effects on these GABA neurochemical assays which could be related to anticonvulsant action. Convulsant activity of benzyl penicillin appears to be related to competitive antogonism of GABA receptors, although the drugs is not very potent or specific. Diazepam at concentrations of50–100 μ M affected GABA transport in a manner consistent with anti-convulsant activity, although at similar concentrations it also could inhibit GABA release and postsynaptic action. Lioresal seems to be a definite GABA agonist, although weak and non-specific, while muscimol is a very potent and specific GABA agonist. Analogues of both these compounds are promising candidates for treatment of neurological disorders involving GABA dysfunction.

Membrane permeability changes during stimulation of isolated salivary glands of Calliphora by 5-hydroxytryptamine.

1. The membrane resistance of isolated salivary glands was found to decrease in response to 5-HT. The change in resistance was calcium-dependent. 2. The resistance change of the apical membrane was found to be much greater than the change in resistance of the basal membrane. 3. Potential responses under current-clamped conditions showed that one part of the biphasic response to 5-HT (attributed to an increase in chloride permeability) could be reversed and the other part (attributed to an increase in a potassium pump) could not. 4. These observations have been incorporated into a model which, on evaluation, predicts all of the observed potential changes during the action of 5-HT. It suggests that the potential responses reflect changes in the internal chloride concentration produced by the calcium-dependent increases in chloride permeability.

The ionic mechanism for 5-hydroxytryptamine inhibition on retzius cells of the leech Hirudo medicinalis

1. 1. Intracellular recordings were made from Retzius cells in the segmental ganglia of the leech, Hirudo medicinalis, and the leech, Haemopsis sp. 5-Hydroxytryptamine (5-HT) hyperpolarized the membrane potential of these cells. 2. 2. The inhibitory effect of 5-HT was due to an increase in chloride permeability of the cell membrane. No evidence was found for a potassium component in this response. The internal chloride concentration was calculated to be 8·4 mM which gave a chloride equilibrium potential of — 70 mV. 3. 3. Part of the membrane potential was due to an electrogenic pump but 5-HT did not act by stimulating this system. 4. 4. By the use of a specific 5-HT antagonist, mianserin, and by desensitization experiments it was concluded that 5-HT and strychnine (which also had an inhibitory action on these cells) acted via different receptors. 5. 5. It is concluded that 5-HT acted directly on the Retzius cell membrane to increase chloride conductance.

The stimulant action of acetylcholine and catecholamines on the uterus.

The α action of catecholamines on oestrogen dominated guinea-pig uterus is stimulant. The cell membrane is depolarized, membrane conductance is increased, spike discharge is accelerated and tension develops. This action resembles that of acetylcholine though catecholamines are less potent, and, in equiactive concentrations, catecholamines have a longer latency and a longer duration of action. Evidence, obtained by modifications of the ionic environment, indicates that the depolarization by acetylcholine is due to an increase in sodium and calcium permeability and that acetylcholine can release calcium from intracellular stores. The depolarization by catecholamines is due to an increase in chloride permeability and, in addition, sodium is required for the ensuing increase of spike discharge. Catecholamines produce an increase in the force of contraction, long outlasting their immediate stimulation. Moreover, their effect on membrane potential and membrane conductance persists in the presence of lanthanum. These results suggest that Ca release from intracellular stores may be the primary effect produced by the α action of catecholamines and that the increase in the cytoplasmic Ca 2+ concentration may cause the changes at the cell membrane.