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G Friedlander

Publications and source records attributed to G Friedlander.

At least 73 records · Page 4Linked to original sources
PubMed1995

Lipopolysaccharides stimulate Na-dependent transport in alveolar cells and protect against oxidant injury.

We have evaluated the effect of lipopolysaccharides (LPS), endotoxins from gram negative bacteria, on sodium-coupled amino acid and phosphate transport by alveolar epithelial type II cells and on their alteration induced by oxidants. Alveolar type II cells were obtained by enzymatic digestion of rat lung and grown for 24 h prior to incubation with LPS and then exposed or not exposed to H2O2 (2.5 mM; 20 min). LPS (10 micrograms/ml, 24 h) induced a significant increase in the Na-dependent component of alanine and phosphate uptake while they decreased Na,K-ATPase activity measured by ouabain-sensitive 86Rb influx. We showed that this stimulatory effect i) was independent from macrophage products since it was not mimicked either by supernatant of LPS-treated alveolar macrophages or by pretreatment with tumor necrosis factor and/or interleukin 1 and ii) was dependent on protein synthesis since it was abolished by protein synthesis inhibitors cycloheximide and actinomycin D. Moreover, LPS blunted H2O2-induced decrease of Na-dependent alanine and phosphate uptake. This protective effect of LPS against H2O2 injury i) was independent of macrophage products, ii) was abolished by cycloheximide, and iii) was not associated with either changes in extracellular H2O2 clearance or catalase and glutathione peroxidase activities. We conclude that, in alveolar type II cells, LPS stimulate sodium-coupled transport by a process involving protein synthesis and partially prevent H2O2-induced decrease of Na-coupled transport without discernible change in antioxidant activities.

Alanine↗
PubMed1995

Role of adenosine on glucagon-induced cAMP in a human cortical collecting duct cell line.

The hormonal responsiveness profile of the cortical collecting duct varies from one species to another. To identify the hormones and agonists that modulate the functions of this tubule segment in the human species, we generated a cell line (HCD) immortalized by SV40 virus. The tubular origin of this cell line was assessed by the expression of collecting duct-specific antigens and the ability of vasopressin to increase by nine-fold cAMP synthesis. Glucagon and adenosine stimulated cAMP synthesis, and atrial natriuretic peptide stimulated cGMP synthesis in a concentration-dependent manner. Bradykinin, adenosine and angiotensin increased intracellular calcium concentration ([Ca2+]i). Because adenosine can regulate tubular functions, we examined its role on glucagon-induced cAMP synthesis. Using adenosine analogs, we demonstrated that HCT cells both expressed adenosine type-2 (A2) receptors which stimulated cAMP production, and adenosine type-1 (A1) receptors linked to [Ca2+]i increase which inhibited glucagon-stimulated cAMP synthesis. The inhibitory effect was abolished by pertussis toxin, and was neither due to [Ca2+]i increase nor to protein kinase C activation, which indicated that some A1 adenosine receptors were directly negatively coupled to adenylyl cyclase. These results suggest that adenosine can modify human cortical collecting duct functions in opposite ways according to the adenosine receptor activated.

Adenosine↗
PubMed1995

Oxygen metabolites modulate sodium transport in gerbil middle ear epithelium: involvement of PGE2.

The middle ear epithelium and respiratory epithelia share basic properties such as homeostasis of air-filled cavities and mucociliary clearance toward the pharynx. With the middle ear SV40-transformed (MESV) cell line, we used the short-circuit current (Isc) technique to investigate changes in ion transport induced by oxidants. Xanthine and xanthine oxidase on the basal side of the monolayers dramatically increased Isc up to 50%. This effect was not affected by superoxide dismutase or mannitol, but could be blunted by catalase or 1,3-dimethyl-2-thiourea. Increasing concentrations of H2O2 from 10(-5) to 5 x 10(-4) M produced a dose-dependent increase in Isc from 0.26 +/- 0.16 up to 4.21 +/- 0.43 microA/cm2 (P < 0.05, n = 5). Concentration of half-maximal stimulation (EC50) was 4.68 x 10(-5) M. This effect was inhibited by indomethacin and was related to a sodium transport, since the H2O2-induced increase in Isc could be prevented or abolished by 1) apical addition of benzamil (10(-6)M) and 2) substitution of sodium with N-methyl-glucamine. H2O2 exposure also induced indomethacin-sensitive increase in released prostaglandin (PG) E2 (EC50 = 5.62 x 10(-5) M) and in cAMP content (EC50 = 3.95 x 10(-5) M) with similar kinetics. These results suggest that exposure of MESV cells to oxidants stimulates the production of PGE2, which in turn increases the transepithelial sodium transport rate.

Animals↗
PubMed1995

Parathyroid hormone stimulates ecto-5'-nucleotidase activity in renal epithelial cells: role of protein kinase-C.

PTH-induced phosphaturia is exerted in part by cAMP added to the renal tubular lumen under the influence of the hormone. Modulation of renal phosphate transport by luminal cAMP requires degradation of the nucleotide into adenosine by brush-border membrane ectoenzymes, among them ecto-5'-nucleotidase (5'-NU). Hormonal modulation of 5'-NU activity was evaluated in cultured opossum kidney cells. PTH (1-100 nM) stimulated 5'-NU in a time-, concentration-, and protein synthesis-dependent manner. The effect of PTH-(1-34) was mimicked by PTH-(3-34), which does not activates adenylate cyclase, and by phorbol 12-myristate 13-acetate (PMA), but not by forskolin or (Bu)2cAMP. Down-regulation or pharmacological inhibition of protein kinase-C (PKC) abolished the effect of PTH fragments and PMA. PTH fragments increased intracellular Ca2+ and translocated PKC activity to the membrane. PTH or PMA did not affect 5'-NU messenger RNA content. Inhibition of sodium-phosphate cotransport by extracellular cAMP was decreased by 5'-NU inhibition and was magnified by PTH. These results indicate that 1) PTH stimulates 5'-NU activity in renal proximal tubular cells in a manner involving PKC activation and de novo protein synthesis; and 2) this effect participates in PTH modulation of renal phosphate transport.

5'-Nucleotidase↗
PubMed1995

Adult-onset idiopathic phosphate diabetes. I. Chronic pseudoinflammatory back pain and osteopenia.

STUDY OBJECTIVE: to investigate clinical, laboratory test, and bone mineral density abnormalities in 19 adults with phosphate diabetes of unknown etiology diagnosed in a rheumatology department on the basis of a maximal rate for tubular reabsorption of phosphate (TmPO4/GFR) of 0.77 or less. RESULTS: there were 14 males and five females with a mean age of 36.7 years (range 20 to 68 years) at symptom onset and 43.9 years (24-70) at diagnosis. Seventeen patients (90%) had back pain and 13 (68%) had nerve root pain. The pain was nocturnal only or both nocturnal and diurnal in 14 cases (74%). Other manifestations were fatigue (n = 7, 37%), myalgia (n = 6, 32%), fracture (n = 6, 32%), renal colic (n = 4, 21%), and pseudodepression (n = 10, 53%). Laboratory test abnormalities were as follows: serum phosphate, 0.72 mmol/L (0.58-0.89); rate for tubular reabsorption of phosphate, 74% (54-84%); maximal rate for tubular reabsorption of phosphate, 0.58 (0.4-0.76); urinary calcium/urinary creatinine > 0.48 in nine patients (47%); and fractional potassium excretion > 20% in seven patients (37%). Normal values were found for serum levels of Ca++, Na++, Mg++, creatinine, cortisol, T3, T4, TSH, 25(OH)D3, and 1,25(OH)2 D3. Tests for glycosuria and amino aciduria were negative. Bone mineral density measurements showed z-scores of -2.13 (+0.9 to -4.25) at L2-L4, and -1.34 (+1.5 to -3.2) at the femoral neck. Bone histology showed osteoporosis with a mild increase in osteoid deposition. CONCLUSIONS: idiopathic adult-onset phosphate diabetes manifests as chronic back pain and nerve root pain, sometimes with fatigue and depression. Bone mineral density values are decreased and histology shows osteopenia. Differential diagnoses include spondyloarthropathy, disk disease, fibromyalgia, and depression. Determination of the maximal rate for tubular reabsorption of phosphate is the only means of establishing the diagnosis.

Adult↗
PubMed1994

Glucocorticoid inhibition of Na-Pi cotransport in renal epithelial cells is mediated by protein kinase C.

The effect and mechanism of action of glucocorticoids (GC) on Na-Pi cotransport were evaluated in opossum kidney cells. Dexamethasone (1-1000 nM) inhibited sodium-dependent Pi uptake in a time- and concentration-dependent manner. Inhibition was maximal after a 6-h incubation with dexamethasone and was prevented by cycloheximide and actinomycin D. The effect was related to a 37% decrease of the Vmax value after incubation with 100 nM dexamethasone. The effect of dexamethasone was mimicked by cortisol and blocked by GC receptor antagonists RU38486 and progesterone. GC affected neither glucose or alanine uptake nor Na/H exchange activity. Inhibition of Pi uptake persisted when Na/H was blocked by amiloride or dimethylamiloride. GC had no effect on basal or parathyroid hormone- and forskolin-stimulated intracellular cAMP content. Dexamethasone and extracellular cAMP, parathyroid hormone, or 3-isobutyl-1-methylxanthine had additive inhibitory effects on Pi uptake. Staurosporine, GF109203X, or calphostin C (three dissimilar inhibitors of protein kinase C (PKC)) and PKC down-regulation blunted the inhibitory effect of glucocorticoids on Pi uptake. GC increased both membrane-bound PKC activity and the membrane/cytosol PKC activity ratio. This is the first report of GC activation of PKC in renal cells, which appears to mediate the steroid inhibitory effect on Pi transport.

Aldosterone↗
PubMed1994

Adenoviral-mediated gene transfer to renal tubular cells in vivo.

The efficient introduction of genetic material into quiescent renal cells is potentially important in the study of renal physiopathology and for gene therapy of kidney related disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding the nuclear beta-galactosidase was either selectively perfused into the renal artery or infused through a retrograde catheter into the pyelic cavity of the left kidney of adult rats. Highly efficient gene transfer was achieved by either route of administration, and nuclear beta-galactosidase activity was detected for two to four weeks following a progressive decline of expression. Genetically-modified cells were identified as proximal tubular cells when the adenoviral vector was selectively perfused via the renal artery, while tubular cells from the papilla and medulla were selectively transduced by retrograde infusion of the viral vector. No obvious cytopathic effect was observed. We conclude that: (i) efficient gene transfer in renal tubular cells can be achieved by adenoviral vectors; (ii) the targeted cell population can be chosen through the route of administration.

Adenoviruses, Human↗
PubMed1994

Local action of phosphate depletion and insulin-like growth factor 1 on in vitro production of 1,25-dihydroxyvitamin D by cultured mammalian kidney cells.

The hormonal form of vitamin D, 1,25(OH)2D, is synthesized mostly in proximal renal tubular cells. Experimental and clinical studies suggest that the growth hormone may be involved in growth-related fluctuations of plasma 1,25(OH)2D and in the increase of 1,25(OH)2D induced by in vivo phosphate deprivation, an action possibly mediated by insulin-like growth factor 1 (IGF 1). We tested the effects of phosphate depletion and IGF 1 addition on 1,25(OH)2D3 production in cultured kidney cells: opossum kidney (OK) cells, LLC-PK 1, and rabbit's proximal tubular cells. Confluent cell monolayers were preincubated in various phosphate concentrations, in the presence and absence of IGF 1. Then, 5 nM of [3H]25 (OH)D3 or 2 microM of 25 (OH)D3 were added to the medium and the cells were incubated for a further 120 min. The amount of biosynthesized 1,25(OH)2D3 in lipid extracts was determined after two different straight phase high performance liquid chromatographies. The experiment showed the following: (a) LLC-PK 1 and rabbit's cells expressed a detectable ability to synthesize 1,25(OH)2D3, while OK cells did not. (b) Partial or total phosphate deprivation increased the amount of 1,25(OH)2D3 produced, respectively in LLC-PK 1 and in rabbit's cells. (c) IGF 1 (25 ng/ml) increased 1,25(OH)2D3 production in rabbit's cells, particularly in phosphate-free medium (1.6-fold), and in LLC-PK 1 cells, in partial phosphate depletion (2.75-fold in 1 mM phosphate, P = 0.015, n = 5, and 3.2-fold in 0.5 mM phosphate, P = 0.043, n = 4). Our findings demonstrate a local action of phosphate depletion and of IGF 1 on 1,25-dihydroxyvitamin D3 production.

Animals↗
PubMed1994

Cellular mode of action of parathyroid hormone.

The current understanding of the cellular mode of action of PTH has undergone deep changes during the last decade and the major acquisitions can be summarized as follows. First, results from biochemical and cell biology studies suggest the existence of at least two receptor types coupled to two distinct intracellular signaling pathways by G proteins: the phospholipase C-calcium-protein kinase C pathway would be coupled to high-affinity receptors, whereas the adenylate cyclase-cAMP-protein kinase A pathway would be coupled to low-affinity receptors. Until now, only one type of PTH receptor has been identified at the molecular level. It is very likely that additional PTH receptor types will be evidenced. Second, both PTH receptor-coupled transduction pathways are involved in the inhibitory effect of the hormone on the activity of two transport systems of the apical membrane of proximal tubular cells: Na-Pi cotransport and Na-H exchanger. These effects are the cellular basis for PTH inhibition of Pi and bicarbonate reabsorption. Which proteins are the targets of the different protein kinases remains to be established. Concerning the other effects of PTH on the proximal tubule (stimulation of neoglucogenesis and of calcitriol synthesis, and Na, K-ATPase inhibition), protein kinase C seems to play a major role. Third, in Henle's loop, PTH stimulates reabsorption of divalent cations through a dual effect under the dependence of protein kinase A, i.e., enhanced epithelial potential difference and opening of paracellular pathway. Finally, stimulation of distal calcium reabsorption results from multiple events: membrane insertion of apical calcium channels, opening of basolateral chloride channels resulting in cellular hyperpolarization, and modulation of Ca-ATPase. Again, while it is commonly acknowledged that both transduction systems are involved, their precise molecular targets remain to be identified (Table 1). The elucidation of the cellular mode of action of PTH, some examples of which have been reviewed, holds major interest far beyond the field of cell or organ physiology. It is the basis for understanding and, ultimately, for comprehensive treatment of genetic diseases characterized by functional abnormalities of molecules involved in the cascade of events leading to the effect of PTH on its cellular targets (hormone receptors, G proteins, and kinases). The second perspective is pharmacologic: molecular and structural identification of PTH-receptor interactions will be a prelude to design and synthesis of new selective, nonpeptidic hormonal analogs and antagonists that are easier to handle. The high incidence and severity of secondary hyperparathyroidism during chronic renal failure highlights the importance of this research.

Animals↗
PubMed1993

Middle ear cell line that maintains vectorial electrolyte transport.

The middle ear epithelium plays a major role in keeping the temporal bone cavities fluid-free and air-filled, which is a mandatory condition to allow optimum transmission of the sound vibrations from the tympanic membrane to the inner ear. Previous works have recently established the absorptive function of the middle ear epithelium, using primary cultures derived from Mongolian gerbil (Meriones unguiculatus). Because of the paucity of cells as obtained by enzymatic digestion, we developed a middle ear cell line (MESV) using wild-type SV40 infection of primary culture of Mongolian gerbil's middle ear epithelial cells. Transformation was attested by nuclear expression of SV40 large T antigen, prolonged in vitro passages (presently beyond 50 passages), and tumor-inducing ability when subcutaneously injected in athymic mice. Transport properties were evaluated after the fifteenth passage. MESV cells retained most cardinal properties of the original middle ear epithelial cells: cell polarization was evidenced by the presence of mature junctional complexes that separate the cell membrane in two distinct domains, with apical microvilli at the luminal side, and by vectorial sodium transport responsible for the transepithelial lumen-negative potential difference (-9.3 +/- 0.14 mV in culture conditions (n = 9), -2.1 +/- 0.25 mV after overnight growth factors and serum deprivation). Short-circuit current was, like in primary cultures, mainly related to a sodium transport occurring through amiloride-sensitive apical sodium channels, since apical addition of amiloride (10(-5) M) reduced ISC from 7.0 +/- 1.4 to 0.6 +/- 0.1 microA/cm2 (P < 0.01, n = 6). Cellular cAMP content was increased by isoproterenol and prostaglandin E2 from 40.5 +/- 5.6 to 258.5 +/- 17.3 and 55.6 +/- 6.2 pmol/mg protein per 5 min, respectively (P < 0.05, n = 10). Isoproterenol and prostaglandin E2 increased ISC with very similar maximal effects: isoproterenol (10(-4) M) increased ISC from 5.73 +/- 0.31 to 12.77 +/- 0.39 microA/cm2, while prostaglandin E2 increased ISC from 5.47 +/- 0.21 to 12.87 +/- 0.42 (n = 3). Since amiloride (10(-5) M) abolished this stimulation, this may be related to an increase of the electrogenic sodium transepithelial transport. The MESV cell line could provide an interesting tool as a model of middle ear epithelial cells for the study of pathophysiological modulations of ion transport.

Amiloride↗
PubMed1993

Primary culture of rabbit proximal tubules as a cellular model to study nephrotoxicity of xenobiotics.

The effects of gentamicin treatment on functions of the plasma membrane-bound proteins in situ were investigated in primary culture of rabbit proximal tubular cells (PTC), a recognized model of renal epithelial cells. Activities of apical and basolateral enzymes, activities of phosphate, glucose and alanine sodium-coupled transport systems and leakage of the cytosolic enzyme lactate dehydrogenase (LDH) were determined in PTC grown in glucose-free culture medium as confluent monolayers and incubated with the aminoglycoside. Gentamicin altered in a concentration- and time-dependent manner the activity of dipeptidyl peptidase IV (DPP IV), neutral aminopeptidase (NAP), Na+K(+)-ATPase and the Vmax of sodium-dependent glucose and phosphate uptake, whereas gamma-glutamyl-transpeptidase (GGT) and sodium-dependent alanine uptake were unaffected. Identical concentration of gentamicin was required to induce LDH leakage and cell functions impairment. In contrast, under short time exposure, a condition where the enzyme activities were untouched, mercuric chloride inhibited to a similar extent the activity of the three sodium-coupled transport systems. These data suggest that whereas alterations in membrane fluidity might mediate the effects of gentamicin on membrane functions, the inhibition of transports by mercuric chloride rather reflects an effect on sodium permeability of the apical membrane. They also suggest that study of Na(+)-coupled transports in proximal tubular cells grown in primary culture is a simple and sensitive in vitro model to assess drug-induced nephrotoxicity.

Aminopeptidases↗