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F Lang

Publications and source records attributed to F Lang.

At least 73 records · Page 4Linked to original sources
PubMed2001

Effect of NaPi-mediated phosphate transport on intracellular pH.

Extracellular pH has been shown previously to influence transport via type-II Na+/phosphate (NaPi) transporters by modifying the affinity of the carrier for Na+ and by altering the availability of divalent and monovalent phosphate. As the transport of monovalent phosphate would be expected to acidify, and that of divalent phosphate to alkalinize the cell interior, the effect of phosphate transport on cytosolic pH was studied using ion selective microelectrodes in Xenopus oocytes expressing NaPi-3 or NaPi-5. At an alkaline extracellular pH (pHe) of 8.0, addition of phosphate elicited a strong inward current, depolarization of the cell membrane and cytosolic alkalinization. At pHe 6.0 the phosphate-induced inward current and depolarization were reduced and the alkalinization completely abolished. In conclusion, at alkaline pHe phosphate transport is enhanced and the transport of divalent phosphate prevails. At pHe 6.0, phosphate transport is attenuated and is accomplished by transport of both divalent and monovalent phosphate.

Animals↗
PubMed2001

Electrophysiology of betaine transport in isolated perfused straight proximal tubule.

Betaine is accumulated in proximal renal tubular cells as an organic osmolyte. In theory, concentrative cellular uptake of betaine can be accomplished by the Na+, Cl-, betaine, GABA-cotransport system (BGT-1) cloned from MDCK cells. The carrier mediates the Na(+)-coupled electrogenic transport of organic osmolytes. Cl- may be transported together with Na+ and organic substrate but it is not an obligatory substrate. The expression of BGT is upregulated by osmotic cell shrinkage. In the present study, isolated perfused straight proximal tubules of the mouse were studied using electrophysiological techniques to elucidate the effects of betaine and gamma-aminobutyric acid (GABA) on the potential difference across the basolateral cell membrane (PDbl). Betaine and to a lesser extent GABA added to the bath led to the rapid depolarization of PDbl. The betaine-induced depolarization was virtually abolished in the absence of extracellular Na+ and blunted in the absence of extracellular Cl-. Inhibition of K+ channels by Ba2+ did not significantly modify betaine-induced depolarization. Increases of extracellular osmolarity enhanced, and decreases of extracellular osmolarity blunted, the betaine-induced depolarization. In conclusion, betaine transport across the basolateral cell membrane of straight proximal tubules from the mouse kidney is similar to the transport by BGT in terms of Na+ and Cl- sensitivity but not the apparent affinity for GABA. The sensitivity to ambient osmolarity indicates that betaine transport in proximal tubules is regulated rapidly and nongenomically.

Animals↗
PubMed2001

Na+ transport by the neural glutamine transporter ATA1.

Transfer of glutamine between astrocytes and neurons is an essential part of the glutamate-glutamine cycle in the brain. Here we have investigated how the neural glutamine transporter (rATA1/GlnT) works. Rat ATA1 was expressed in Xenopus laevis oocytes and examined using two-electrode voltage-clamp recordings, ion-sensitive microelectrodes and tracer flux experiments. Glutamine transport via rATA1 was electrogenic and caused inward currents that did not reverse at positive holding potentials. Currents were induced by a variety of neutral amino acids in the following relative order Ala>Ser/Gln/Asn/His/Cys/Met >MeAIB/Gly>Thr/Pro/Tyr/Val, where MeAIB is the amino acid analogue N-methylaminoisobutyric acid. The uptake of glutamine and the corresponding currents depended on Na+ and pH. Hill-coefficient and flux studies with 22NaCl indicated a cotransport stoichiometry 1 Na+ per transport cycle. The transporter also showed uncoupled Na+ transport, particularly when alanine was used as the substrate. Although substrate uptake increased strongly with increasing pH, no change of intracellular pH was observed during transport. A decrease of the intracellular pH similarly inhibited glutamine transport via ATA1, suggesting that the pH dependence was an allosteric effect on the transporter.

Amino Acid Transport System A↗
PubMed2001

Serum- and glucocorticoid-dependent kinase, cell volume, and the regulation of epithelial transport.

Ample pharmacological evidence points to a role of kinases in the regulation of cell volume. Given the limited selectivity of most inhibitors, however, the specific molecules involved have remained largely elusive. The search for cell volume regulated genes in liver HepG2 cells led to the discovery of the human serum- and glucocorticoid-dependent serine/threonine kinase hsgk1. Transcription and expression of hsgk1 is markedly and rapidly upregulated by osmotic and isotonic cell shrinkage. The effect of osmotic cell shrinkage on hsgk1 is mediated by p38 kinase. Further stimuli of hsgk1 transcription include glucocorticoids, aldosterone, TGF-beta1, serum, increase of intracellular Ca2+ and phorbolesters, whereas cAMP downregulates hsgk1 transcription. The hsgk1 protein is expressed in several epithelial tissues including human pancreas, intestine, kidney, and shark rectal gland. Co-expression of hsgk1 with the renal epithelial Na+-channel ENaC or the Na+/K+/2Cl(-)-cotransporter NKCC2 (BSC1) in Xenopus oocytes, accelerates insertion of the transport proteins into the cell membrane and thus, stimulates channel or transport activity. Thus, hsgk1 participates in the regulation of transport by steroids and secretagogues increasing intracellular Ca2+-activity. The stimulation of hsgk1 transcription by TGF-beta1 may further bear pathophysiological relevance.

Animals↗
PubMed2001

Second-line treatment with oxaliplatin + raltitrexed in patients with advanced colorectal cancer failing fluoropyrimidine/leucovorin-based chemotherapy.

BACKGROUND: To evaluate the efficacy and tolerance of combined raltitrexed and oxaliplatin in patients with advanced colorectal cancer pretreated with fluoropyrimidine leucovorin-based chemotherapy. PATIENTS AND METHODS: Thirty-six patients with metastatic colorectal cancer, who progressed while receiving or within six months after withholding palliative chemotherapy with fluoropyrimidines leucovorin +/- irinotecan, participated in this study. Treatment consisted of oxaliplatin 130 mg/m2 and raltitrexed 3.0 mg/m2 both given on day 1 every three weeks for a total of eight courses unless prior evidence of progressive disease. RESULTS: The overall objective response rate was 33.3% for all 36 evaluable patients (95% confidence interval (CI): 18.6%-51%). Seventeen additional patients (47.2%) had stable disease, and only seven (19.5%) progressed. The median progression-free survival was 6.5 months (range 1.2-14.0). After a median follow-up time of 12 months, 23 patients (63.8%) are still alive. The tolerance of treatment was acceptable with only 8 of 36 patients (22%) experiencing grade 3 or 4 neutropenia. Grade 3 non-haematological adverse reactions included peripheral sensory neuropathy in three, asthenia in one, diarrhea in two, and clinically insignificant increase in serum transaminases in two patients, respectively. CONCLUSIONS: Our data suggest that the combination of oxaliplatin and raltitrexed has substantial antitumour activity in patients with progressive fluoropyrimidine leucovorin + irinotecan pretreated colorectal cancer. Because of its favorable toxicity profile and convenient three-weekly outpatient administration schedule, further evaluation of this regimen seems warranted.

Adult↗
PubMed2001

Multicenter phase II trial of dose-fractionated irinotecan in patients with advanced colorectal cancer failing oxaliplatin-based first-line combination chemotherapy.

BACKGROUND: A multicenter phase II trial was initiated to investigate the efficacy and tolerance of a dose-fractionated administration schedule of irinotecan in patients with advanced colorectal cancer pre-treated with fluoropyrimidine/ oxaliplatin-based first-line combination chemotherapy. PATIENTS AND METHODS: 38 patients with metastatic colorectal cancer, who progressed while receiving or within six months after withholding systemic chemotherapy with oxaliplatin in combination with 5-fluorouracil/leucovorin or the specific thymidilate synthase inhibitor raltitrexed were enrolled in this study. Treatment consisted of irinotecan 175 mg/m2 given on days 1 and 10. Courses were repeated every three weeks for a total of six courses unless prior evidence of progressive disease. RESULTS: The overall objective response rate was 21% for all 38 patients (95% confidence interval (95% CI): 9.6% to 37.4%). Stable disease was noted in 19 patients (50%), whereas the tumour progressed in 11 (29%). The median progression-free survival was 4.8 months (range 1.5 to 10.5). After a median follow-up time of 10 months, 21 patients (55%) are still alive. Treatment was fairly well tolerated with only 9 of 38 patients (24%) experiencing grade 3 or 4 neutropenia. Similarly, nonhaematologic adverse reactions were generally mild; grade 3 toxicities included late-onset diarrhoea in 2 (5%), alopecia in 5 (13%), and infection in 1 case (3%), respectively. CONCLUSIONS: Our data suggest that this dose-fractionated irinotecan monotherapy schedule has substantial antitumour activity in patients with flupropyrimidine/oxaliplatin-based pre-treated colorectal cancer. Because of its favourable toxicity profile when compared to previous experiences with the European standard schedule of 350 mg/m2 every three weeks, further evaluation of this modified regimen seems warranted.

Adult↗
PubMed2001

Mechanisms of Staphylococcus aureus induced apoptosis of human endothelial cells.

Staphylococcus aureus plays an important role in sepsis, pneumonia and wound infections. Here, we demonstrate that infection with several S. aureus strains results in apoptosis of human endothelial cells. S. aureus induced an activation of cellular caspases, the acid sphingomyelinase, a release of cytochrome c and a stimulation of Jun NH2-terminal kinase (JNK). The significance of these findings is indicated by a prevention of S. aureus triggered apoptosis of human cells deficient for ASM or upon genetic or pharmacological inhibition of JNK or caspases, respectively.

Apoptosis↗
PubMed2001

A src-like kinase activates outwardly rectifying chloride channels in CFTR-defective lymphocytes.

Defective activation of chloride channels is a hallmark of cystic fibrosis (CF). Recently we have described activation of a volume-sensitive, outwardly rectifying chloride conductance (I(OR)) through the src-like tyrosine kinase p56(lck). Here we show that p56(lck) activates I(OR) independently of CFTR. In lymphocytes from healthy donors, chloride channels could be opened by either intracellular cAMP, p56(lck) or osmotic swelling. In CF lymphocytes, p56(lck) and cell swelling but not cAMP could activate chloride channels. Regulation of I(OR) by p56(lck) thus represents an alternative pathway of stimulating membrane chloride conductance that is left intact in cystic fibrosis.

Chloride Channels↗
PubMed2001

Pseudomonas aeruginosa-induced apoptosis involves mitochondria and stress-activated protein kinases.

Pseudomonas aeruginosa, a gram-negative facultative pathogen, causes severe infections in immunocompromised and cystic fibrosis patients. However, the molecular details of the interaction between P. aeruginosa and mammalian cells are still largely unknown. Here we demonstrate that infection of human conjunctiva epithelial Chang cells with the well-characterized P. aeruginosa strain PAO-I results in rapid induction of apoptosis. Apoptosis was mediated by mitochondrial alterations, in particular mitochondrial depolarization, synthesis of reactive oxygen intermediates, and release of cytochrome c, as well as an activation of Jun N-terminal kinases (JNK). Stimulation of these events was dependent on upregulation of CD95 on infected cells, and a deficiency of CD95 or the CD95 ligand prevented mitochondrial changes, JNK activation, and apoptosis upon infection. Further, efficient apoptosis of Chang epithelial cells required infection with live P. aeruginosa, adhesion but not invasion of the bacteria, and expression of the type III secretion system in PAO-I. The data indicate a type III secretion system-dependent, sequential activation of several signaling pathways by P. aeruginosa PAO-I, resulting in apoptosis of the infected cell.

Animals↗
PubMed2001

Function and structure of heterodimeric amino acid transporters.

Heterodimeric amino acid transporters are comprised of two subunits, a polytopic membrane protein (light chain) and an associated type II membrane protein (heavy chain). The heavy chain rbAT (related to b(0,+) amino acid transporter) associates with the light chain b(0,+)AT (b(0,+) amino acid transporter) to form the amino acid transport system b(0,+), whereas the homologous heavy chain 4F2hc interacts with several light chains to form system L (with LAT1 and LAT2), system y(+)L (with y(+)LAT1 and y(+)LAT2), system x (with xAT), or system asc (with asc1). The association of light chains with the two heavy chains is not unambiguous. rbAT may interact with LAT2 and y(+)LAT1 and vice versa; 4F2hc may interact with b(0,+)AT when overexpressed. 4F2hc is necessary for trafficking of the light chain to the plasma membrane, whereas the light chains are thought to determine the transport characteristics of the respective heterodimer. In contrast to 4F2hc, mutations in rbAT suggest that rbAT itself takes part in the transport besides serving for the trafficking of the light chain to the cell surface. Heavy and light subunits are linked together by a disulfide bridge. The disulfide bridge, however, is not necessary for the trafficking of rbAT or 4F2 heterodimers to the membrane or for the functioning of the transporter. However, there is experimental evidence that the disulfide bridge in the 4F2hc/LAT1 heterodimer plays a role in the regulation of a cation channel. These results highlight complex interactions between the different subunits of heterodimeric amino acid transporters and suggest that despite high grades of homology, the interactions between rbAT and 4F2hc and their respective partners may be different.

Amino Acid Transport Systems↗
PubMed2001

Na(+)/H(+)exchangers: linking osmotic dysequilibrium to modified cell function.

The Na(+)/H(+) exchangers (NHEs) are among the major ion transporters involved in cell volume regulation. NHE activation leads to a cellular influx of Na(+) ions and extrusion of H(+) ions, which are readily replenished from intracellular buffers. This will result in a net import of Na(+). In many systems NHE operates in parallel to Cl(-)/ HCO3(-) exchange, resulting in cellular uptake of NaCl. The influx of osmotically obliged water will consequently lead to cell swelling. This makes NHEs suitable to serve as powerful mechanisms for increasing cell volume (CV). The low volume threshold for NHE activation enables the cells to respond to very minute reductions of the CV. By the coupling to the export of H(+) ions cell volume regulatory NHE activation may lead to changes in intracellular pH. On the other hand NHEs are activated by a broad variety of ligands and by intracellular acidosis, which, in turn, may consequently lead to cell swelling. In addition, NHEs are linked to other intracellular proteins and structures, like e.g. the cytoskeleton, which themelves are involved in the regulation of numerous cellular processes. Therefore NHEs link CV regulation to a diversity of cellular functions, both in physiological and pathophysiological conditions. Six isoforms of the Na(+)/H(+) exchanger, termed NHE1--6, have been cloned so far. NHE 1--5 are located in the plasma membrane, whereas NHE6 is sorted to the mitochondrial membrane. NHE1 and NHE6 are the ubiquitously expressed isoforms. The expression of the isoforms NHE2 to NHE5 is restricted to specific tissues and the pattern of their expression, as well as their subcellular localization indicate that they fulfill specialized functions. Cell shrinkage induced activation has been shown for NHE1,2 and 4. In contrast, NHE3 is inhibited by cell shrinkage. In many cells several isoforms are present and assigned to specific membrane domains where they may serve a functional crosstalk between the different ion transporters.

Amino Acid Sequence↗
PubMed2001

Differential transcription of ion transporters, NHE1, ATP1B1, NKCC1 in human peripheral blood lymphocytes activated to proliferation.

This work, using RT PCR, studied expression of mRNAs encoding ion transporters, the Na/H antiporter (NHE1), the beta subunit of the Na,K-ATPase pump (ATP1B1), the NaK2Cl symporter (NKCC1), and some proteins unrelated to ion transport: the serum and glucocorticoid dependent kinase (hSGK), beta-actin, a glycolytic enzyme (GAPDH), and regulators of proliferation and apoptosis (p53, Bcl-2) during activation of human lymphocytes with phytohemagglutinin for 4-24 h. Within 24 hours the mRNA levels of NHE1, beta-actin, Bcl-2, and p53 increased by more than 100%, the mRNA levels of ATP1B1, GAPDH, and hSGK, by about 50%, while the mRNA levels of NKCC1 decreased transiently. These results indicate a differential transcriptional control of NHE1, ATP1B1, and NKCC1 following a proliferative stimulus of human lymphocytes.

Carrier Proteins↗
PubMed2001

Determination of protein-protein interactions of ICIn by the yeast two-hybrid system.

ICln is a ubiquitously expressed eukaryotic protein. Expression of the protein in Xenopus laevis oocytes, the knocking-down of the protein in fibroblasts, or the reconstitution of the protein in lipid bilayer led to the assumption that this protein is an ionic channel or a significant part thereof. However, other possible roles for ICln in potential regulatory mechanisms have been postulated, as diverse as regulator of cell morphology by interacting with the Skb1 protein and/or interaction with core spliceosomal proteins. Here we show that ICln is able to interact with SnRNP core proteins SmD1, SmD2, SmD3, SmX5 and SmB/B'.

Amino Acid Sequence↗
PubMed2001

Effects of the serine/threonine kinase SGK1 on the epithelial Na(+) channel (ENaC) and CFTR: implications for cystic fibrosis.

Cystic fibrosis (CF) is characterized by impaired Cl(-) secretion and increased Na(+) reabsorption in several tissues including respiratory epithelium. Many CFTR mutations have been identified over the past years. However, only a poor correlation between the genotype and lung phenotype was found suggesting additional factors influencing the phenotype and course of the disease. The serine/threonine kinase SGK1 has recently been shown to stimulate the activity of the epithelial Na(+) channel ENaC. A variety of stimuli such as aldosterone, cell shrinkage, insulin or TGF-beta1 stimulate transcription and activate the SGK1 kinase. Here we further examined the effects of SGK1 on ENaC and CFTR which have mutual interactions and we analyzed sgk1 mRNA abundance in lung tissue from CF patients. Coexpression of CFTR and h-SGK1 in Xenopus oocytes increased ENaC currents as previously described. In addition CFTR mediated currents were also stimulated. h-SGK1 accelerated the expression of the amiloride sensitive Na(+)- current in Xenopus oocytes paralleled by increased ENaC-protein abundance in the oocyte membrane, an effect which was reversed by a h-SGK1(K127R) mutation lacking the ATP-binding site. The cation selectivity or Na(+) affinity were not affected. However, coexpression of h-SGK1 with ENaC altered the sensitivity of the Na(+)-channel to the inhibitors amiloride and triamterene. The inhibitory effect of CFTR expression on ENaC current was not affected by coexpression of h-SGK1 in Xenopus oocytes. Lung tissue from CF patients strongly expressed the serine/threonine kinase h-sgk1 which was not the case for non-CF lung tissue. Loss of CFTR function itself in a CF lung epithelial cell line did not increase SGK1 expression. In summary, enhanced expression of h-SGK1 in epithelial cells of CF-lung tissue may be a novel pathophysiological factor contributing to increased Na(+) channel activity and thus to increased Na(+) transport in CF.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Effects of gallium and mercury ions on transport systems.

Mercury was previously shown to exert toxic effects by influencing ion channels and transporters in the kidney and brain. Gallium alloys were suggested as less toxic restorative materials. To compare the toxicity of gallium ions with those of mercury ions, we applied gallium nitrate Ga(NO3)3 (0.1-100 microM and mercuric chloride (HgCl2) (0.001-10 microM) to Xenopus oocytes expressing mammalian ion channels and transport proteins. Mercury (10 microM) inhibited the K+-channels ROMK and HERG, the phosphate transporter NaPi-3, the amino acid transporter rBAT, the cation transporter OCT-2, and the osmolyte transporter BGT. It activated the I(Ks)-channel but did not affect the Na+-channel ENaC, the anion channel NaPi-1, and the glucose transporter SGLT-1. Gallium was without significant effect on the channels and on SGLT1, NaPi-3, and rBAT, but inhibited BGT and OCT-2. In conclusion, both Hg2+ and Ga3+ may exert toxic effects on transport systems, which may partially explain their cytotoxic effects.

Amino Acid Transport Systems↗
PubMed2001

Factorial structure of the Sensation-Seeking Scale-Form V: confirmatory factorial analyses in nonclinical and clinical samples.

OBJECTIVE: The factor structure of the Sensation-Seeking Scale (SSS)-Form V was studied in 2 large French samples, using confirmatory factorial analyses (CFA) to test the 4-dimensional model of sensation seeking postulated by Zuckerman. METHOD: The study included 769 healthy subjects and 659 patients who met the DSM-IV criteria for substance use disorders or eating disorders and completed the SSS. The correlation matrices for each of the samples were analyzed using CFA. RESULTS: In each sample, we found the 4-factor model to be replicable. CONCLUSION: The multidimensionality of sensation seeking is supported by the results, and the 4-dimensional model of sensation seeking identified by Zuckerman can be explored in French-speaking people.

Adolescent↗
PubMed2001

Synthesis of N-pyridinyl(methyl)-1,2-dihydro-4-hydroxy-2-oxoquinoline-3-carboxamides and analogues and their anti-inflammatory activity in mice and rats.

The topical anti-inflammatory activity of a series of N-pyridinyl(methyl)1,2-dihydro-4-hydroxy-2-oxoquinoline-3-carboxamides, analogues of roquinimex, has been evaluated by measuring their inhibitory effect in the phorbol myristate acetate (PMA)-induced mouse ear swelling test, used as a screening test. All the eight carboxamides tested (9-16) exhibited significant inhibitory activity at 0.4 and 0.2 mM kg(-1). The most potent compound, the 6-bromo derivative 12, induced a 73% inhibition at 0.2 mM kg(-1). Pharmacomodulation was carried out by heterocycle opening and molecular simplification leading to pentafluorobenzoylacetamide 17, pentafluorocinnamamides 18 and 19, and pentafluorobenzaldimines 20 and 21. All the five compounds exerted a reduction in swelling (49-63% at 0.2 mM kg(-1)) comparable with ibuprofen (56%). Anti-inflammatory activity of the most efficient compounds was evaluated by carrageenan-induced rat paw oedema inhibition. The pentafluorobenzaldimine 20 showed the highest activity with an inhibition percentage of 85% at 0.2 mM kg(-1).

Animals↗